HomeMy WebLinkAboutAPA3340SUMMER DISTRIBUTION, NUMBERS, AND FOOD HABITS
OF THE GYRFALCON (Falco rusticolus L.) ON THE
SEWARD PENINSULA, ALASKA
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APPROVED:
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=n-ea_n_o---:r:;--·-the College of Biological {J
Sciences and Renewable Resources
~ // C::..---CL~--------------Vice President for Research and
Advanced Study
SUMMER DISTRIBUTION, NUMBERS, AND FOOD HABITS
OF THE GYRFALCON (Falco rusticolus L.) ON THE ----------
SEWARD PENINSULA, ALASKA
A
THESIS
Presented to the Faculty of the
University of Alaska in Partial Fulfillment
of the Requirements
for the Degree of
MASTER 0~ SCIENCE
By
David Gale Roseneau, B.S.
College, Alaska
Hay 1972
ABS'l'RAC'I'
During the summers of 1968, 1969, and 1910
aerial and ground surveys were made of approximately 17,000
square miles of the Seward Peninsula, Alaska, to locate
nesting Gyrfalcons (Falco rusticolus L.). During the three
summers 131 nestings were observed and populations remained
both high and relatively stable on a region-wide basis.
He-utilization of specific nest cliffs was low, however,
and cliff-shifting was conspicuous. In smaller areas of
the peninsula the numbers of pairs utilizing a given area
changed from year to year in a manner correlat8d with prey
availability.
Prey remains and pellets were collected from 37
nests over the course of the study and 1,483 kills were
identified. A minimum of 40 speci.es was represented includ-
ing 32 bird species and eight mammal spec~es. This is a
considerably longer list of prey species than has been
reported previously. Four species dominate the food sample
(Rock Ptarmigan, Lag onus mutus, 1di llo1·r Ptarmigan, L. la;;:;opus,
the Arctic Ground Squirrel, Sp~rmophilus undulatus, and the
Long-tailed Jaeger, Stercorarius longicaudus), making up 81
per cent by number and 92 per cent by weight. Prey utiliza-
tion va~ied with availability both from year to year and
from habitat type to habitat type beti'Teen the hunting ranges
of nesting pairs.
iii
ACKNOVJLEDGiviENTS
I would like to express my appreciation to the
organizations and persons who supported and encouraged
this study. The Alaska Department of Fish and Game
supported the project during 1968 and 1969 (under Project
No. W-13-r-3 and W-17-l, Work Plan B, Job No. ll, and
under Project No. W-17-l and W-17-2, Study Plan B and R,
Job No. B-ll and R-10.4). In 1970 this agency supported
the analysis of food habits data (under Project No.
W-17-3, Job ~o. B-11 and R-10.4). Dr. Robert B. Weeden,
formerly a biologist with the Alaska Department of Fish
and GE~me and Project Leader, deserves special mention for
his encouragement and valuable comments. The Nome office
of the Alaska Department of Fish and Game, under the
leadership of John Burns in 1968 and 1969 and Robert Pegau
in 1970, provided outstanding cooperation and assistance
throughout the course of the study. Edward Muktoyuk,
Carl Yanagawa, and Peter Kashiverof lent valuable assis-
tance and information.
The National Audubon Society funded a major portion
of the study during 1970. Their financial support and
encouragement during 1970 made it possible to complete
this thesis.
The University of Alaska and the College of Biologi-
iv
cal Sciences and Renewable Resources provided additional
necessary support and funds throu~hout the course of the
study. My special thanks go to Dr. L. G. Swartz, academic
advisor and teacher. His encouragement, advice, and
friendship were of the best throughout my academic career.
William Griffin, Alaska Department of Fish and
G~me biologist, Neal W. Foster, Foster Aviation, and
George Johnson, Foster Aviation, piloted various portions
of the aerial surveys throu~hout the study--a sometimes
dangerous and tryins job. Their combined expertise and
cooperation made Lr1e uerial survey possible and lent much
towards its success.
Dr. C. L. Sainsbury and Travis Hudson of the United
States Geological Survey contributed valuable cooperation
and assistance throughout the course of the field work.
Wayman E. Halker, fellow graduate student at the
University of Alaska, assisted in field operations during
1970. As an 2blc co-worker and excellent conpanion, he
shared my enthusiasm for birds of prey.
William R. Tilton assisted with field work during
1968. He contributed a high level of enthusiasm, undamped
spirits, and a keen eye.
:Patrick Wright worked as my field assistant du~ing
a'port:lon-of the_1969 field season.
Sam Stoker donated valuable time during a memorable
v
exploration of the peninsular coast between Nome and
Unalakleet in 1969.
vi
TABLE OF CO~TENTS
:!:NTRODUC'l'ION.
OBJEC'l'IVES.
f!IETHODS . .
Study Area . . . .
Numbers and Distribution .
Food Habits.
RESULTS .
Numhers and Distribution .
Population Changes .
Food fiabits.
Prey utilizat5on on the
Yearly variations in prey utilization .
Variation in prey species utilization
between different pairs .
SUMMARY AND CONCLUSIONS .
LITERATURE CITED.
vii
l
3
4
4
6
8
13
13
23
1!1
it 1+
59
121
123
'l'able
l.
2.
3 .
lj .
5 .
6 .
7.
LIS'l' OF ':::'J\BLES
Numbers and densities of breeding Gyrfalcon
pairs on the Seward Peninsula, Alaska .....
Successive use of nesting cliffs by predatory
birds on a 20-sauare-mile nortion of the
Seward Peninsul~, 1968-1970. . . . ..
Soecies utilizing the 34 active Gyrfalcon
nesting cliffs observed on the Seward
Peninsula, Alaska, 196R-1a70 ..
Species utilizing the 48 active 1969 Gyrfalcon
nesting cliffs observed on the Seward Penin-
sula, ~laska, 1968-lq7o. . . . . . ..
Collection dates of Gyrfalcon prey remains
Total 1968-1970 Gyrfalcon food remains
The three major Gyrfal~on food items ..
8. Total migratory bird species identified
from the 1968-1970 Gyrfalcon prey remains
and listed in various important gro~ps . .
9. 1968-1970 Gyrfalcon food rem8ins
on a yearly basis ....
corn-quted
10. Migratory species identified from the 1968-
1970 Gyrfalcon prey remains compared on a
yearly basis and listed in various important
groups . . . .
11. Comparisons of the occurrence of nine prey
groups in Seward Peninsula Gyrfalcon prey
remains computed on a yearly basis . . . -.
-12a.-Gyrfalcon eyrie no~ 1, Seward Peninsula,
-.A-laska . . . . . . . . . . . . . . . . .
12b~ ·GYrfalcon food_remains from ~able l2a grouped
. irt various major food categories ...... .
vij_i
13
19
32
45
46
48
52
62
tSB
85
86
Tab1e
13a. Gyrfa1con eyrie no. 2, Seward Peninsula,
AJ.aska ..........•
13b. Gyrfalcon food remains from Table l3a grouped
in various major food cate~ories.
14a. Gyrfa1con eyrie no.
Alaska ...•.
3, Seward Peninsula,
lJ.tb. Gyrfalcon .food remains fran rrable J.lta grouped
in various major food categories.
15a. Gyrfalcon eyrie no. 4, Seward Peninsula,
Alaska. . . . . . . . . . . . . .
15b. Gyrfalcon food remains from Table 15a grouped
16a.
in various major food categories ...... .
Gyrfalcon eyrie no.
Alaska .....
5, Seward Peninsula,
16b. Gyrfalcon food remains from Table 16a grouped
in various major food categories.
17a. Gyrfalcon eyrie
Alaska ...•.
no. 6, Seward Peninsula,
17b. Gyrfalcon food remains from Table 17a grouped
in various major food categories.
18a. Gyrfalcon eyrie no. 7, Seward Peninsula,
Alaska. . . . . . . . . . . .
18b. Gyrfalcon food rer:1ains from 'l'able 18a grouped
in various major food categories.
19a. Gyrfalcon eyrie no. 8, Seward Peninsula,
Alaska. . . . . . . . . . . . . .
l9b. Gyrfalcon food remains from Table 19a grouped
in _various major food. categories. . . . -. .
20a. .. Gy-rfalcon eyrie ·no. ·9, Sevrard Peninsula,
Ala sleet. ·, . . . 0 • • • • • •
20b; ·Gyrfalcon food remains from Table 20a grouped
in various major food categories. . ...
ix
87
88
89
90
91
92
93
95
97
98
99
100
101
102
Table
21~. Gyrfalcon eyrie no. 10, Seward Peninsula,
Alaska. . . . . . . . 103
2lb. Gyrfalcon food remains from Table 2la grouped
in various major food cate~ories. 104
22a. Gyrfalcon eyrie no. 11,
Alaska .....
Seward Peninsula,
22b. Gyrfalcon food remains from ~able 22a grouped
105
in various major food cateGories. 106
23a. Gyrfalcon eyrie no.
Alaska .....
12, Seward Peninsula,
23b. Gyrfalcon food remains from Table 23a grouped
107
in various major food categories. lOB
24a. Gyrfalcon eyrie no. 13, Seward Peninsula,
Alaska .. 109
24b. Gyrfalcon food remains from Table 24a grouped
in various major food categories. 110
25a. Gyrfalcon eyrie no. 14, Seward Peninsula,
Aln.ska. . . . . . . . lll
25b. Gyrfalcon food remains from Table 25a grouped
in various major food categories.
26a. Gyrfalcon eyrie no. 15, Seward Peninsula,
112
Alaska. . . . . 1J.3
26b. Gyrfalcon food remains from Table 26a groured
in vario 1,lS ma:j or food categories. 1111
27a. Gyrfalcon ~yrie no. 16, Seward Peninsula,
27b.
28.
Alaska. . . . . 115
Gyrfalcon food remains from Table 27a grouped
in various major food categories.
. . . -·
The range in the per cent occurrence and
~numbers of the· three ma,j or prey :categories,
~igratory bird species, and resident species
at 23 SeNard Peninsula Gyrfalcon nestings . ~
X
116
ll'T
Fir;ure
1. The Seward Peninsula, Alaska, showing the
boundaries of the 1968-1970 substudy area,
the approximate tree line and the 162°00'
Vl. meridian. . . . . . . . . . . . . . . . . .
2. Percentage occurrence of selected ~roups
of prey species in summer Gyrfalcon nrey
remains from the Seward Peninsula, Alaska,
1968-1970. . . . . . . . . . ....
3. The percentage occurPence of ptarmigan in
the 1968-1970 Gyrfalcon prey remains com-
pared with an observed subjective estimate
of ptarmigan population trends from the
Seward Peninsula, Alaska ..... .
4. The percentage occurrence of jaegers in
the 1968-1970 Gyrfalcon prey remains com-
pared with an observed subjective estimate
of jaeger population trends from the Seward
Peninsula, Alaska. . . . . . . ....
5. The percentage occurrence of microtines in
the 1968-1970 Gyrfalcon prey remains com-
pared with an observed ~;ubj ecti ve estimate
of microtine population trends from the
Seward Peninsula, Alaska . . . . . . . . .
6. The percentage occurrence of Arctic
. .
Ground Squirrels in the 1968-1970 Gyrfalcon
prey remains compared with an observed
subjective estimate of the ground squirrel
population trends from the Seward Peninsula,
Alaska . . . . . . . . . . . . . .
7 .. (A) The estimated biomass o~ ~tarmigan and
Long-tailed Jaegers calculated as a per-
._~entage by weight of the avian remains,-and
(B) the estimated biomass of Arctic Ground
,Squirrels c-alculated as a ~}ercentage by
-weight of the mammalian remains identified
-·rrorn-the' 1968-19'{0-Sevrard r·eninsula· Gyrfalcon
PTeY remains . . . . . . . ... . .. . . .
xi
15
69
'{l
73
75
79a
Figure
8 . Major Gyrfalcon prey iters expressed as a
percentage of the total of yearly kills by
weight: (A) ptarmigan, jaegers, ground
squirrels; (B) ptnrmi~an, ground squirrels;
(C) ptarmigan, jaeGers; (D) ground squirrels,
j aegers. . . .
·-_...,
xii
82
INTRODUCTION
The Gyrfalcon (Falco rusticolus L.), largest of
the falcons, is found north of 59° N. Latitude around the
world. It is the Arctic counterpart of the desert falcons,
considered by Otto Kleinschmidt (as cited in Voous, 1960)
"as the arctic form of the semi-cosmopolitan group of the
Saker (Falco cherrug Gray) and Lanner (Falco biarmicus
Temmincl:c). 11 This species is closely assocj_ated with tree-
less arctic and alpine terrain, and is adapted for catch-
ing birds and small mammals on or near the ground.
In Alaska, the Gyrfalcon lives and breeds through-
out the foot-hills of the Brooks Range, the De LA nO' ....... ....., ...... D
Mountains, the Baird Mountains, the Bering Sea coast and
Seward Peninsula, the high uplands between the Yukon and
Tanana Rivers, the foot-hills of the Alaska Range, the
hills between th~ Kuskokwim River and Bristol Bay, parts
of the Alaska Peninsula, and (almost certainly) some of
the larger islands in the Aleutian Chain. They also have
been ~aid to breed sparingly on Kodiak and Nunivak Islands
and .. possibly on St. Lawrence Island ( Cade, 196-o). · Cade
.(1960} mentions the Talkeetna and Chugach Mountains as
. . . -
add~tl.~nal possible habitats. I have kno't'l-ledge of at .
. least; three -su:ccessful nestings· (Roseneau, ~unpublishe-d)
----o.·-_· ·-:J· . ~--... --
... ,_ . : --. ----· ---
1
2
~~, ------------------------------------~~ - -------------------------------
1971) in the Chugach Mount~ins. Breeding may also occur
in portions of the Chigmit Mountaihs (pers. observation).
Prior to the present study, little was known about
Alaskan Gyrfalcon populations, their numbers~ and food
habits, except from Cade's (1960) research. -Cade collected
data from portions of the Arctic Slope from the Colville
River in the Brooks Range and relied heavily on Alaska
Range data collected by Murie (1946, unpublished), M. w.
Nelson, and J. H. Doyle. He further attempted to piece
together all breeding records of Gyrfalcons in Alaska and
to summarize what little was known about food h~bits.
Cade' s data indicated that the highest densi_ties of Gyr-
falcons. were likely to be found in western Alaska,
adjacent to the Bering Sea (including the Seward Peninsula).
He Estimated the entire Alask~n population to be.between 200
.and 300 pairs.
._._c'4 ---_j
OBJECTIVES
This study was formulated to pursue the following
specific objectives: 1) to determine the summer distri-
bution and numbers of Gyrfalcons on the Seward Peninsula,
Alaska; and 2) to determine the food habits of breeding
Gyrfalcons.
Often studies of predatory animals are confined to
relatively small areas by logistic and other problems,
and I feel that this is unfortunate. Predators in
general tend to be more thinly· distributed than the mem-
bers ofrlower trophic levels and for this reason, studies
of small areas are likely to be representative of highly
local conditions and to suffer from small sample sizes.
Accordingly, I have attempted to study Gyrfalcons over a
very large area, an area which also possesses the advan-
tage of bein_g well circumscribed geographically. This
study was intended to be broadly applicable to the breed-
ing range of the Gyrfalcon and thus to permit extrapolation
and perspectives on Gyrfalcons in the whole circumpolar
·zone.·
·-.;:·.;.._
. ~
METHODS
Study Area
The Seward Peninsula is the westernmost extension
of mainland Alaska .and, because most of it seemed likely
to be comprised of good Gyrfalcon habitat, it was chosen
as the major study area. Although one aerial search was
made east of Golovin, the formal study was conducted west . I
of 162° W. Although·potential Gyrfalcon habitat exists
east of-162° W., only one aerial survey was made east of
that line due.to logistical factors. A portion of the
major study area was selected as ~ sub-study area for in-
.~--
\"_) tensive investigation near Nome and is described later
(see Figure 1). Extensive g~ourid and aerial work was done
during the periods 24 May through 30 August 1968, 22 May
through 15 August 1969, and 23 May thr9ugh 25 August 1970.
The Seward Peninsula is situated between 64° 30'
N~ and 66° ·30' N. Although the region lies at approximately
· the same latitude as Fairbanks, vlhich is in the center of
typi·car·sub-arct·ic boreal forest, maritime influences help-
create biotic conditions on the Seward P~ninsula th~t_are
·arctic-1ri nature. The tree-line stops at a north-south
line_ rep~¥sent_ing _?.pproximately 162° · 32' i'J., and the
·-·-·...... ·-.
peniri~t!J~a-i-s ~practically t-reeless Nes·t of this line. Hov-1....,
··-ever? some _·sprue~ forest extends Nest along the· southern
_-{)~·-lJ ..
' l
j l
' 1 ~
1
coast to Golovnin Bay and northwest up the Nuikluk River
valley tri a ~oint approximately 15 miles upriver f~o~-
Coundil. Scattered spruce continue almost to the North
Fork of the Nuikluk River and reach the southern and
eastern portions of McCarthy'~ Marsh.
The topographic profile is characterized by low
rolling hills, generally under 1,500 feet elevation. The
land is drained by a complex network of shallow rivers and
tributa~y creeks, many of which usually become dry by mi~
July. Four small mountain rang~s exist .
. . The York Mountains, near the western tip of the
peninsula, are barren and rugged, rising abruptly from the
5
-~ -0 sea to become high rolling tundra-covered hills a few miles
riorth and offer few suitable outcrops but afford some sea-
cliff sites. The Darby Mountains northeast of Golovnin
Ba.y e~tend north to merge with the more centrally located
Bendeleben range. ~he Darby Mountains contain a large
section of granite intrusives in the southeast section pro-
viding -many spires and "blocks:' suitable for -·large cliff
·nesting raptors. The Bendeleben Mountains are extensiVely
-weathered and rounded. The Kigluiak r11ountai11s, just south··
·~ .. of the·kuZ'itrin River_ and Imuruk .. Basin, are-rugged and rise
abruptly~:f:rom -relatively lor! e·levat·ion. A large section
_of the· J;_~iij_n_sula riO'rth of'-the .. Be-ndele ben rl!ounta1ns contains
· numel"cOU:s -.-c.inder .. cones and is covered by geologically recent
-'~,3 ~ava ·flows. : Cinder cones and kett.le lakes cover much of
-. :"'·.;;:.··-··:-=.·.:,-: -··
6 ..
the Cape Espenberg sector north of 66° N .
. Rock outcrops, often of limestone or its meta-
morphic products, occur commonly throughout the peninsula.
These outcroppings tend to face south. River bluffs occur
on som~ of the larger rivers and ~orne small canyons exist
along deep-cutting streams. Sea-cliffs are limited to a
few important stretches of coast east of Nome, the.Grantley
Harbor and Tuksuk Channel area, the York Mountain section
·between Lost River and Tin City, and some sections of the
northern coast between the Goodhope River and the Buckland
River.
Numbers and Distribution
In 1968, exploratory work began on the outskirts
of Nome and continued along the three major roads (to
Teller, Taylor~ and Council) as theY opened to vehicular
i·
traffic. r1ost of_ tbe intensive ~1o·rk on study eyries was
. -·
done on foot and with road vehicles. Snow machines were
utili2ed from arrival through mid-Jun~ to explore areas
well off of the roads. Rivers were crossed on foot and
occasionally by canoe. A skiff and a 38 foot inboard
" patrol-vessel (-lent to the Alaska Department of Fish and
-pame by-. th.e Department-of the Army) were used for coastal··.
·-trave·l~eastl.,rard and westward from Nome. A Cessna 180 and
. -----·
-a PA...:.l8~:Super Cub. were used f-or the aerial surveys. My· -
0
7
previous familiarity with Gyrfalcon nesting requirements
and s~tuations often allowed me to travel on the ground or
in aircraft directly to likely nest sites.
Aerial survey te6hniques were developed which
allowed me to 16cate nesting cliffs, nest sites, riount
young in the nests, and, in some instances, observe eggs.
Ratcliffe (1962a) has defined the.concepts of nnesting
cliff, !t "nest site, n and "eyrie. •! His definitions will be
followed-throughout the text of this thesis. Low level
flights wer~ cqnducted during June and early July and on
favorable days lasted up to 6 hours~ Optimum flight dura-
tion was 3 td 4 hours; beyond this time, fatigue and eye-
.) strain affected efficiency. PA-18 Super Cub flights were
--~_./
manned by a pilot experienced in aerial· survey operations
and one observer; an additional observer covld be accommo-
dated on C~ssna 180 flights. Total search hours flown
wer_~; PA:....r8 Super.Gub, 32.2 hours; Cessna 180, 13.1 hours.
Efficiency in the Cessna 180 was initially mar-
ginal because of higher speeds and reduced visibility from
the aircraft-windows. -· With experience, efficie·ncy using
the Ces_sna 180 · i.ncreased reaching a. level· comparable vd th
the -s~l-ewer PA-18 Super Cub by May· 1970. United States·
.. : .Geo.l6gfcQ.l S1lrvey topographic maps of scales ~1: 63000 and
1:2500-"QO'""'.were-.:used to .record poidtions.-A Sony. Model·
··-·
--~ -" .... _ .. -:"-::·: .. :-;._:_·--_:;:_._ -.. · .
T_C-lQO_:-cassette ·tape recorder was used_ to record aerial
./""~ ~.~obs_e~~a-~io~~~ .. Access to nests visited on foot was gained
·(~
·.~)
_c:J
a
by routine rock-climbing techniques.
Methods used in 1969 and 1970 were identical to
those described for 1968 with a few exceptions. Snow
machines were not employed i~ 1969 or'l970 bec~use of early
snow-melt. In 1969 26.9 search hours were spent in a PA-18,
8.8 in a Cessna 180. In 1970, the aerial survey was con-
ducted solely from the Cessna 180 aircraft (28.4 hours).
One helicopter trip to a remote sectcir was provide~ by
Standard Oil Company geologists in late July 1970. During
all three years of the study, various men from the. U. S.
Geological Survey, particularly Dr. C. L. Sainsbury, pro-
vided valuable information and assistance.
Food Habits
Collection· of the uneate.n portions of prey i terns
(hereinafter referred to as "prey remains"), along with
reg~rgitated pellets, were made from all accessible occu-
pied nesting sites. Prey remains were analyzed tb deter-
mine the prey species utilized for food by nesting
Gy:rf.a],_cons. Although an .analysis of pellets vias made
for -c-omparative purposes, prey remains received the major
emphasis-··· Pellets, with the· ex·ce-ption of t_beir m.icrotine
c_onten.ts, were_ less informative' due to the qualitative
.. -
nature of-the-contents ··anti to the fi:rct that· upon-arialysfs
the pellets rarely off~~ed evidence of prey specie~ other
·--. . . .
than .tbos;e .already represented in the prey remains (with
-..:.:. "'" _.
-. _.;:.:,. ·,:r
•··
\ . ..
' 1
''·
1.· ~
.C-.'::;-" ~-
·~ ----
the exception of microtines).
Regurgitated pellets and prey remains were
collected from 10 nesting sites in 1968, 14 nesting sites
in 1969, and 16 nesting sites in 1970 {see Table 5,
9
page 115). On the first visit to a nest site, a 1'c1ean-up:'
of the nest and its sur~oundings was made. Weathe~ed
pellets and remains. were discarded, and only fresh speci-
mens were co1l~cted, leaving the places of accumulation
cl~an of food residues. On subsequent visits only those
resid~es ahcumulated by the breeding pair would be present·
in the sample·. Outcrops, ridge tops, and ·grassy hummocks
in the immediate area were search~d todetermine the loca,..
(~ tions of favorite perching places. Pellets fo~nd away
from the known perches or the nest were discarded since
usually they could not be attributed to any one species of
raptor (Weir, 1967). Throughout the summer, the.nearby
slop~~ were criss-dressed o~ foot; additional kills usually
in the form o-f-.. a ring of plucked ptarmigan feathers were
noted. The.m&jority of the samples came from the occupied
nests,-the· slopes directly beneath them, ahd the two or
three pr~mary perching piaces nearby.
--: .~...; ... ~ Tne tables were constructe.d using data from .the.
. . . -·: ..
remailJ.S collected at these locations. These remains
·. ·l:lS1laiJ;i:.,G,Rn.si_!;3ted of actual skeletal material with adhering
3.. . fle.slr:,=rur) or feathers. r ... . . . .
\ were u':S7j~J.i,y: ~mitted, since almos.t all such feather-rings
Feather-rings on the nearby slopes
·. --.-----~---~~----~-.-~--;_:_:_: .... ---_:_=-:-· ~:. ;-·---
... ___ ·_-_...:::------.. .-/ .. ::-_··-:-
:~
I
I
I
1
1
.. ,·,
10
represented ptarmigan (Lagopus lagopus and Lagonus mutus)
in winter plumage and were obviously from the previous
winter or early spring. It was gen~rally impossible to
determine if feather-rings .from a prey species represented
other kills of that species or if they belonged to the
skeletal remains of that species collected from the nest
area.
When searching·a nest for ~neaten remains a
careful search was made for sig-nificant small feathers or
skeletal material, in recognit~on of the fact that.the
larger avian and mammal remains would be the most conspi-
/~ cuous and, therefore, most often recorded species
J (Errington~ 1932). This search usually produced passerine
and/or microtine remains hidden in the nest litter.
Collect~ons made at .each riest sit~ were placed
in-labeled plastic bags. It \'las common to find portions
(feet' feathers-, etc.) from two or three separate kills or
the same· species at the perching -and -plucking places. Each
-set was·pla6ed in its individual plastic bag before being
added to-the total collection.
The collection from any one eyrie on any one date
------.
was treated as.follows: ·each labeled pl~stic bag w~s
vented to ~llow drying and to prevent mold and decomposition
-. ·''-·"""
--. -and-p.l'ace-{r-fn -a labeled paper bag; with a liberal quantity
-. . . -. -0 of na~·ttrti""c~rystal:s. -These bags l-lere stored in a cool, dry
place whenever possible and, once remains were safely dry, _
.·..-:···
I .
.:
11
...---,..
C .. -· •. ~ ~--'1_ .. ' -~:J--------
.y
• .. J
the sealed paper bags were packed in cartons for shipment
to Fairbanks.
Identification of the skeletal material, feathers,
and other uneaten portions was carried out during 1970 and
1971 at the bird and mammal collection of the University of
Alaska ..
Whole pellets were broken apart and examined for
content. In the majority of cases, the pellets were com-
·-..
po&ed.of mammal hair, small bones~ and feathers from the
heads, necks, and breasts of birds (as described by Bond,
1936). Pellets resulting from a meal of· ptarmiga-n commonly
contained the antebra,chium and the manus and often the
humerus of a wing, or the tibio-t~rsus, tarso-metatarsus,
phalanges, and often the femur of a leg. Rarely did the
examination of a pellet reveal signs of a species not
alrea<;ly-present among the uneaten prey remains. In almost
&11 ca~e~ sp~cies represerited in p~llet contents were pro-
portioriaL to those. found in the corresponding prey remains.
Evidence of microtines was more often found in pellets than
in prey remains (by a factor of about five). This indicates
;··-~ that rriicrotiile rodents are ta."ken to a greater degree than
t.·muld·-be·assumed· if only prey remains .are examined .
.. c ~-·· .::.-. 'Pe.ilet examination tends to reveal qualitative,
but-not ~.<I£antita~~ve, information (Erringt.on, 1930,. i·932L
. ·,~ · 'rheref_ol'e; only the uneaten portions of prey l"emains were
used to~:pev(:?lop a quantitative picture· of Gyrfalcon diet in
l!!lll!lll ••• A&Mi,W.Ai'"•.ww . · =·
-~
I
t
j
I !
i
·I !
I
j
I
12
northwest~rn Alaska.
..
·•
.-.. •.o;,_:_-":].
-_·· . .:c·_---~--~ -J
RESULTS
Numbers and Distribution
The major sttidy area comprises approximately
17,000 square miles of potential Gyrfalcon habitat, _and
includes essentially the whole Sevrard Peninsula. Virtually
all of this large area was examined from aircraft or on the
ground. The first survey flights conducted in 1968 served
to familiarize me with the topog~aphy and terrain of the
Seward Peninsula. By aerial observation, it became clear
that because_of geologic and altitudinal-factors some-areas
were essentially devoid of nesting sites. The Kigluiak
.'!f"
() t•lountains are steep,· with crests averaging about · 3, 000 feet
above sea level. Valleys are narrow, barren, and do not
·o
~upport an abundance of prey species. More important, out-
crops suitable as nest sites are rare. The surrountling
hills are rounde~d-~nd are. also not ch~racterized b~ rock
outcrops. ~In the eourse of thi_:.3_ study; no cliff...;nesting
raptors have been observed in this region.
In contrast to the rugged Kigluiaks much of the
--.
Bendele ben range is vvell weathered and-rounded. Some
scatt~red·rock outcrops do occur, most in the form of tors,
but f-:m,r:offer suitable ledges for nest construction. A
few su1"tab1e out~croppi-ngs exist~ primarily along· the v1ater
--._, . ,• ~: -·--. . '
co-urses,-generally not far above the valley floors. A rela-
.. ·.-· 13
14
tively small number of nestings occurred in the Bendeleben
Mountains; the few outcrops available were not heavily
utilized.
Rock outcrops are rarely encountered in the
marshes, poastal plains, lava flows, and broad low basins
associated with the larger iriland river systems; c6nse-
quently, few nesting sites are available. Rock outcrops
do occur in upland 11 hilly" regions, ln faulted areas, on
some upland benches, on the shoulders of some hills, and
along some water courses. ·Granitic intrusions in some
wel.l-fau1~ed zol}es have produced spires and.tors well
suited as nesting sites. A relat~vely small proportion of
'~ '"_) the coast line offers sea-cliffs suitable for nesting .
..
The sub-study area (Figure l) covers about 2,400
square miles and includes the rugged Kugluiak Mountains,
coastal marshes and plains along the southv-1estern coast,
and t~o relatiVely minor stretch~s of s~a cliffs. ·The
remaining po_rtion of th~ · s.ub-study area; primarily. s-outh
of the Kigl~i~k Mountains, is good nesting habitat and is
charact-erized by---high . ( 1, 000. to 2, 000 ·reet} rolling hills-
-. -·. -.
· interlaced by 12 relat·i vely short--( 16 to 40 -mfies) ·drainage
syst~fus. A-l~rge part of this-hi~ly regiort consists of
. metamorph).(J schist: and limestone. These tl'io basic rock
types are,_.interspersed and lend themselves \'lell to the
formati-on of numerous outcrops and tors through faulting,
--··-..,_ . . ' ·. . ' . . ···-
.-t) _foldj_ng,: .. thrust.ing, and erosion. These outcrops and tors . "-==' . . . . , ... ----· .· ...
,... . ··.'···_; ....
.. ·-, --.....
1
I
·'
'i
i;
' . ,
N
'.
Bo!lndary of substudy area
Serg.Hot .
0Spgs.
'f0.0,· T. ayior v ' ~
0 -~
?
Tree· line .
(approximate)
..
'!
Figure L • The Set-rard Peninsula; Alaska, sho~Ting the boundaries
of the 1968 -1970 substudy ~rca, the approximate tree line and
the 162°06 1 .W meridian.
16
are heavily utilized by Gyrfalcons and other cliff nesting
"· spec.ies. This area includes about 1, 000 square iitiles and
has been designated as Area I.
The remaining approximately 14,600 square miles
of the Sew~rd Peninsula includes the Darby Mountains, the
Bendeleben Mountains, and the rqgged York Mountains.
These ranges interrupt the general pattern of rolling 1,000
to 2,000 foot hills and are interlaced by numerous ~tream
systems. , .This general pattern of tundra covered hills has
a few exceptions; a large lava and cinder cone-covered area
.lies between the Bendeleben Mountains and Imuruk Lake an«
extends west to a point near the junction of the Kuzitrin
,· C) River and the Noxapaga River. A.large marshy lowland basin
contains the extensive Kuzitrin and Noxapaga River systems
and Imur~k Basin. These river systems and surrounding
pattern of tundra ponds drain into Imuruk Basin north of
the .Ki·gluia:k-P.fountains. An additional large area (about
2,500 square miles) extending from Wales to the mouth of
_ the Goodhope River consists of wet lowland tundra with
ext-ensi-ve systems of sloughs,. ponds' and rivers flm-iing
·into large --·coitstallagoons • F-inally, a Sp·ruce. forest
.. .extends ·ove·r .an eastern portion of the peninsula· (see
Figure :~11". In all, about four to five thousand square miles
of the Seward ·Peninsula outside of the sub-study area are
rarely utilized by nesting Gyrfalcons because of the lack
of suitable. nesting sites.
. I
I (
i ~
I l i
17
In the remaining 9,600 to 10,600 square miles,
the occurrence of suitable outcrop~ i~ generally low,
though these-outcrops are important to Gyrfalcon pairs as
nesting cliffs. These outcrops tend to be widely scattered
or concentrated in small unevenly distributed clusters,
with one important exception--an area of about 1,200
square miles in the central-western portion of the perrin-
sula where numerous _outcrops occur. This area has been
desi~nated Area II for purposes of discussion. Area II is
simila~ to Area I in that it consists mainly of schist and
limestone~ --·In a:ddi tion, Area> II has ·a.' maJor faulted zone
running through its northern half. Igneous r.ock in t.he
,c-~
···-J form Of granitic intrusions ITO'i'T existing as large granitic
tors occurs where a second important fault trenp intersects
the first. These large complex formations are contained
_ within a relatively small 20 square mile portion of Area ~I
~hd-offer many suita~le fiestin~ sites (~ee Table 2).
.Ruril)g 1,968, 1969, and_ 1970, the sub-study area
(Figure 1) was given comprehensive aerial and ground cover-
age. -This region of---about -2,4 00 square mi:les contains
about _140· outcrops suitable for nesting by at least one of
three srecile~ of cliff-nesting raptors-~Gyrfalcons,
Rough--fegged HaNks (Buteo lagopus), and Golden Eagles
--
(Aquila chrysaetos}. These outcrops also serve as potential
-nesting c~ltffs for Ravens -(Corvus cor ax) . Thirty-eight of
Q the 140 -q_uterops are known to be suitable as Gyrfalcon-
w I '
.
I I
!'
.
l
I
I
I
1
1
l
i
i
Table 1. Nur.tbers and densities of brE>edins Gy1•falc~n pairs on the Scw:~rd Penlr.sula, Alaska
Area ~·
Sub-study 2 .~oo
Area_ r 1,000
Ar.ea ;u -1-,200
==-=T=:
~
1968
1969
1970
3 years
1968
1969
1970
3 years
-1968.
1969
1970
3 years
~Uctivc Nes~
19 1
1~2
1.2.
52 x = 17.3
16
12
16
~~
X "' 111.7
42
126.3
171.4
!._?£.,.)_
62.5
83.3
62.5
X =
171.4
·75.0
63.16
18
I
I
I
/~ X = 14.0 x = io3.2 ,I
I }Area II 1,200 Good coverage years
. (1969, 1970) "'../
Entire Seward
Peninsula
(West o:r 162° W.)
·· Entire Seward
Peninsula
(West of 162° W.) _
17,000 1968
1969
1970
3 years
Good coverage years
(1969, 1970)
35
131
97
X:= 17.5
113.7
i .. 48.5
500.0
354.2
3116.9
i = 401.3
R = 350.5
I f ~ i· I ~-I
lrn add1 tion, one other n:ti r '~-"'-~ l<"c"t~':l th'lt -=i\;;~._.'!,.;;;~-to~<t1re-l<'st.::ct'fJ.::c.;:t ,:;-iil.JI:r.h-=-ffi--;-t="=t;~E'1 fluf!rlc:...-:._-=--~ ~ =-=--=--=-----=-=jjj
to frequent the nesting cliff until about mid-July. _ ~;
?-one additional single bird was foun~ defending an outcrop where only an empty nest was .i
~epeatedly obse~~ed from-the-a~rcraft. ·
~
3rh1s area received poor aerial coverage durin~ 1968, which resulted in what is certainly a ~
lower number of nestings that actually occurred. The total number listed for 19E3 reflects ~
this. -I
I I r: ~
~ i
I 0 ..
., ... ~.~.--,._. -~-_/
'.
Table 2~ S~ccesslve use or nestin; clirrs 1 by predatory birds on a 20-squnre-mlle rortion or. the
Sol;:ll'.d Peninsula, 196:3-1970
19
_ .. ______ "'="'* ..,..
~~--=-
Site No. Use in 1~68 Use in lCJ~O llse ~!1 1970
l Gyrfalcon
2 Gyrfalcon
3 Rough-Legged Hawk Rough-Leg~ed Hawk Rough-Legged Hawk
lj Rough-Ler:ged Eawk Rour.;h-I.er;ged Hawk
5 Golden Eagle Golden Eagle prer;ent 2
6 Raven
7 Gyrfalcon Gyrfaleon3
8 Gyrfalcon
9 Gyrfalcon
10 Gyrfalcon·
11 Rou,;h-Legt;ed Hawk
12 Rough-Ler;ged Hawk !\
13 r.aven __ _)
14 Raven
15 Gyrfalcon
16 Rough-Lege;ed 'Ha~1k
17 Rough-Legged Hawk
18 Rou~;_h-T.cgr;ed F.awk
19 Rough-Legged Hawk
20 Ro:~t;h-Le::r;e<i ~at·!~-':'
21 -Rough-Legged ·Hawk
22 Raven
23 Unidentified
NOT ·usED-BY ANY-SPECIEs· DURING 1968 -1970
36
··-,AU these cUffs have at least -one old stick nest Ol' an eyri.e ledge fprr.1ed. by the rem-'l.ins or a
·stick nest on them. . _ . · · · · · · .
2At 1east one tllcd...spent cons.l.cie-rable time here and was observed·. a nu:nbe:-of times b:Jt no evidence of breeding was found. .
3Th is t<~as-·the same pa1r based o'n color and behavioral characteristics.
/ 1 f--
\ t' ~
....... ---
-. -.-.
20
nesting cliffs. Gyrfalcons were observed utilj_zing these
outcrops over the three-year study period; reliable local
residents reported that Gyrfalcons had used six additional
outcrops prior to 1968. About 30 more outcrops appear to
be useable based on comparisons of cliff height, ledge
size, and the presence of old, large stick nests.
Table 1 lists the numbers of breeding Gyrfalcon
pairs.and their relative densities for the Seward Peninsula
including three sub-areas. During the 1969 survey a
decrease in the number of breeding pairs was observed in
the sub-study area and in its sub-unit, Arei I. This
decline amounted to about 25 per cent and occurr~d in a
. . .
year when some important prey p6pulations declined and 1vill
be discussed further in the Food Habits section. In 1970
the number of breeding ~airs·was found to have returned to
. 'th~"l968 leveL. :This ~ccurr~q in a 'year when SOITle impor-.
. -. -. ·-- -·_ -. -. ' -. . .
. --- ---
tant prey species populations appeared to have recovered. to
a level somewhat below the 1968-"high" but· markedly above
that of. the 1~.69 "low". (see Food Habits section) •
·· Duririg. the course of the study,' 52, or 39.7 per
cerit of the 131 total Gyrfalcon nestings observed on the
pehinsul~, occurred within the appro-ximately 2 ,lfOO square
mile sub-study area. Forty-four, or 33.6 per cent of--the
131 tbtal Gyrfalcon nestings, occurred within the approxi-
(-~ mately 1,009 square mile Area I. Of the 52 total Gyrfal_con \_~; .
. nest~ngs~pbserved within the sub-study area, ?4.6 per cent
I .
.
.
' -~
:-'
;~---,..Jc
---.., __ -'
21
occurred in Area I.
Area II was discovered during the last survey
flight conducted in 1968. Thorough coverage was not possi-
ble that season. In succeeding years (1969 and 1970) Area
II was given thorough coverage. The mean density figure
from 1969 and 1970, omitting 1968, is probably a reasonable
representation of Area II although it lacks the full per-
spective of all three years of the study. -During the
course of the study, 42, or 32.1 per cent of the total 131
.Gyrf~lcon nestings observed, occurred within this approxi-
mately l, 200 squa-re mile area. Combining both areas of
/"~--good nesting .habitat {Area I and Area II), 86, or 65.7 per
',_J cent of all observed nestings, occurred \td thin only approxi-
mately 2,200 square miles or about 13 per cent of the Seward
Peninsula.
Within the ~ntire 17,000 square miles of the
--
Seward Peninsula (west of 162° W.) a total of 131 breeding
pairs of Gyrfalcons with a mean density of about one pair
per 40i-square miles was observed over the course of the
study. -Because I was unf~miliar wit!! the terrain and a
larger portion of the 1968 search time (about one half) h'as
uti.lize-<i to locate areas of concentration and re-check-
--
poasible riesting situations, I consider the 1968 total of
·--:-:-.. -::-:.· -···
34 hre_eding Gyrfalcon pairs to be low and not representative
@ of the Sewar~ Peninsula as a \'.Jhole for that year. In 1969,
. -a t-0tai e£:--48 breeding pairs of Gyrfalcons \'las found, and in
·.---::-:-·" ----'-"'-"'2-~--:.:;. _ ..
-·--=-~-_,_ •.. .; •. _____ .,__
22
1970 a t9tal of 49 breeding pairs (Table 1). The mean
density for these two years is aboat one pair per 350
square miles. This figure, in my judgment, is minimal for
the Seward Peninsula, but may be representative of a few
other areas of upland coastal habitat in western Alaska.
From the present data it appears that Cade (1960)
was ~orrect in attributing high densities of Gyrfalcons to ·
the Seward Peninsula and the western coast of Alaska
-ad~acent t6 the Bering Sea. He reported from Eskimo in-
formation (the reliability of whl9h he was uncertain) that
there were 11 30 known nesting areas· on the Seward Peninsula."
It is the Seward Peninsula supports more
breedirig Gyrfalcons than any other area of comparable size
in Alaska when prey levels are high.
I have p~eviously estimated (Roseneau, 1970) the
total S·evmrd -Peninsula Gyrfalcon popul'ation during abunda.nt
prey years at ·about 70 pairs. This e~timate is based on
aerial views of.the eritire peninsula and knowledge of the
availability of nesting site~ in some areas that were not
.intensively surveyed. ·Assuming the estimate to be accurate,
i t .. ls pos_si~.le t_hat densities of Gyrfalcons on the · SeNard
-. . -. .
Pentnsti~?. -IJ1ay-.be as higp as one pair per 24 3 square miles
·· .for the~s:e -T7-j.ooo -square mile?.• -
-tade (1960) estimated the total Alaskan Gyr-
,3 falcon P.ORI!lation including both breeders and non-breeders
to be 2o:o t.o. 3.00 pairs. Because of the lack of Alaskan
"
'
'-23
s.~-:--.:'"2.1con data, he felt that an "adequate conception of :the
z.::. z:::: of the Gyrfalcon population in Alaska" could not be
:> ... _::--_:_·J.lated. The Seward Peninsula generally has an unusually
..:_~-;:;-:: number of Gyrfalcons. While it is doubtful that many
l~€'= areas of habitat as good as the Seward Peninsula
ez~st in Alaska, very little of inland Alaska has been
e::.:~ined, with the exception of some river courses. Aerial
~~~~~naissance is desirable before reliable population esti-
~~~es can be made, but it is possible th~t the total popu-
:~~:on ~h Alaska during good years may exceed Cade's
/-~ .. \J :?r:..::~..:: ~at ion Changes
Little information on changes in Gyrfalrion popu-
~~~:ons is available. Cade (1960) has summarized the
=c~~~Y work on Alaskan populations and best sums up'the
2 ~::~-=-~tion Nhen he states: "Mount McKinley Park and the
cr:..:~!lle River are the only two-regions of Alaska where any
-z::.:-~:: of' continuous record of the numbers of Gyrfalcons has
b~~~ kept." Iri Mount McKinley Nati6nal Park data are
3 -r-,~:::-'se. Cade (from Dixon, 1938, and Murie, _1946) cites
~:;_-:_7 :"·i-V-e known nesting cliffs_ supporting a· maximum _of
--~---·. ·. ··-----: .. :~-
-"::?~:-o'=~ pai~s"_in _any single year. The Col ville River data
.. ..:-·
-~:·:::-::-:=::..:::at·e--a· population of three pairs of Gyrfalcons inhabi-
_-~~~!~g_1~~-~pper~and middle reaches of the river in 1952.
~@.':•::--::?-59;'--:~~bl~ sanie stretch of river -supported 12 pairs.
'-1
. I
/·~{·
~-ecce=)
· ........ _______ ./
24
During those two years peregrine numbers remained rela-.
tively constant (17 pairs in 1952 and ~5 pa~rs in 1959).
In another example from the Colville, a maximum of six
pairs of Gyrfalcons have bred in any one year (1959), with
an average over five years of oniy 2.6 pairs (Cade, 1960).
Apparent numerical conflicts in Cade's data make the total
counts for 1959 uncertain (pages 177 and 256, Cade, 1960).
On the Seward Peninsula during good survey cover-
age years (1969 and 1970), a relatively constant number of
breeding pairs was found. In 1968, only 34 breeding pairs
wer~ located, but this almost certainly reflects the poor
..
survey coverage. In addition) 1968 was vihen the
abundance of prey species (including two major food species)
was the greatest (see Food Habits section). So far my data
suggest that on a regional basis Gyrfalcon populations,
within. these large areas of nesting habitat, remain rela-
-tively constant, at least on the Seward Peninsula.
Fluctuations in numbers did occur within some
areas of the Seward Peninsula. These fluctuations in
numbers of breeding pairs are similar to those commonly
mentioned throughout most of the Gyrfalcon literature, e.g.,
·cade (1960) and Hagen (1952).
~ln one 20 square mile porti6n of A~ea II offering
abundant bUtcrops, careful ground and aerial reconnaissance
located a minimum of 36 potential nesting cliffs showing
signs of' }:f;t'evious use by at lea~t one of the four large
. :;-·;.·.· .·
. '
~~-.'J-~ --
,-,_ -\
25
cliff-nesters found on the Seward Peninsula (Gyrfalcons,
Rough-legged Hawks, Golden Eagles, and Ravens). Of these
36 potential nesting cliffs, about half appea~ed to off~r
nesting conditions similar to most known Gyrfalcon eyries.
Twenty-two of the 36 cliffs wer~ observed to be utilized by
the four cliff-nesting species over the period 1968 to 1970.
Table 2 presents the history-of occupation of the nesting
cliffs in this small section of Gyrfalcon habitat. It
would appear that this relatively small and isolated
~ -. . .. . -
11 community 11 of large cliff-nesters, including Gyrfalcons,
is in-a constant state of flux.
In another area, an approximately 50 mile section
one pair of Gyrfalcons breeding on it
in 1968, two pairs irt 1969, and five pairs in 1970. On
another large inland river (over 100 miles long) only five
nesting cliffs occur. In 1968, one was occupied by Ravens
.and fourwere unus~d. Iri 1969, the cliff used by the Ravens
-·
was occupied by Gyrfalcons. Of the four unused cliffs
occurring on the same bank of a one-half-mile stretch of
the river, one was unused, one was occupied by Gyrfalcons,
one was g~eupied ·by Rough-legged Ha11,rks, ··and one was
occupiedby Ravens. In 1970 Ravens were nesting again at
-. .. -
·thei:r 1968 cliff. Of the other four cliffs, Gyr.falcons
again use·d?·their 1969 site. Ravens used the 1969 Rough-
i
I
I
l . l
l
i
·.,'\~··.-.--···
!;;,.:;::.-------~ ..---.
26
legged Haw]< cliff and Rough-legged Ha~'lks used the 1969
Raven site. The one nesting cliff with a well-constructed
large stick nest situated under an overhang offering excel-
lent shelter had remained unused all three years.
In one five~mile stretch of creek in 1968 I
found eight nesting cliffs. Three of these were occupied
by bree~ing Gyrfalcons, three by breeding Rough~legged
Hawks, and two were empty. In 1969, this same section of
creek was utilized by three pairs of Gyrfalcons. A pair
of RoUgh~legged Hawks inhabited on~ of the remaining five
nesting cliffs. In 1970, only one Gyrfalcon pair was
found nesting in the vicinity of the creek (four miles
no~th), and one of the 1968 Gyrfalcon eyries was being
utilized by a pair of breeding Lesser Canada Geese (Branta
canadensis).
In two successively larger areas of habitat,
Ar~a I arid the_sub-study area, variation in yearly riumbe~s
of breeding Gyrfalcons occurred (Table 1). Area I, sub~
stu4y area, lost four pairs in 1969. The larger sub-study
area lost five pairs this same year. Considering both
areas separately, both-experienced a decline in breeding
Gyrfalcon.pairs of about 25 per cent in 1969. The 1969
.·decline ~can be attributed in part to a decline in some of
the important. food species (see Food Habits section). ''.rhe
yearly rilimbers of Rough-legged Hawks and Golden Eagles
. ··11 .. ~ '
_..c-~
27
(i.e., breeding pairs) support this hypothesis. In the
sub-study area, 28 pairs of Rough-legged Hawks bred in 1968,
only 8 pairs in 1969, and 35 pairs in 1970. In 1968 seven
pairs of breeding Golden Eagles were present, in 1969 only
tv10 pairs, and in 1970 again seven pairs. The Rough-legged
Hawk numbers, in particular, clearly reflect the 1969
microtine "crash." It is possible that the decline in
breeding numbers of Gyrfalcons in the sub-study area also
refle6fi'the microtine crash as well as a simultaneous
decline in the ptarmigan population (see Figure 3 and
Figure -5).
Frequent references are~made in th~ literature
'_J to the apparent response of Gyrfalcons to microtine and
@ -
-
ptarmigan cycles (Dementiev,and Gortchakovskaya, 1945;
Hagen, 1952; Cade, 1960; Gudmundsson, 1970; Bengtson, 1971).
Gyrfalcon~ are reported to be nonexistent cr scarce breeders
if! many areas during microtine or ptarmigan "lows."· It
should be noted that these areas tend to rep~esent situa~
ti6ns in which Gyrfalcons are d~pendent primarily on these
two ~ategories of food. Dementiev and Gortchakovskaya
(1945) did not_ find an interdependence betv1een Gyrfalcons
and lemniiiigs-and-'suggests Gyrfalcon utili-zation of a sea
bird-·colb:riy as. an explanation.
=.-..;.
:-~There are indications that some· food species,
notably,~tarmigan, Long-tailed Jaege~s, and microtine~, did
I
I I
I
I I
I I
I
1 l
l
I
_j
i . I
l
'
-~~J----
I
'
not decline to the same degree ·in the northern half' of'
the Seward Peninsula during 1969 as they did in the
southern -half. --If t-hese indications ·are correct, one
_ !1Jight speculate that numbers of raptors, including sorrie
Gyrfa~cons, shifted breeding activities to the northern
parts of the peninsula in response to this situation.
28
Although Rough-legged Hawks were not of primary
concern, nest locations were noted. Only six occupied
nest ~it~s were observed in 1968 in the northern half of
the peninstila; About six more pairs were observed from a
distance and were_ probably breeding in this sector. A
higher concentration (28 pairs) occurred in the southern
·(:
--~ -'\; __ .__) sub-study area. In 1969 34 breeding pairs of Rough-legged
Hawks were found in the northern half of the peninsula,
but only eight breeding pairs were evident in the sub-study
area. 1970 appeared to be a year of general abundance for
Rough-legged Hawks over th~ entire Seward Peninsula •. -
'J.lhirt_y-five pqirs were found nesting -in the sub-study area
and_38·pairs ih the northern half 6f the p~ninsula. In
1969-, when 14 breeding pairs of Gyrfalcons inhabited the
sub-st~dy areai more nesting p~i~s ~er~ evi~ent in a strip
-north of· t-he sub-study area" but south of Area II;-.. -
--_In a very large region of habitat,_ such as the
};7_, OO __ p _§q)J.a~e miies-of the Seward Peninsula conside;red in
__ this ·study,-· the numbers of Gyrfalcons probably remain rela-
(J tively c~c)nstant unless a major portion (or all) of the
/~
region is affected by drastic changes in prey population
size, availability, or vulnerability.
Cade (1960), speaking of Gyrfalcons, states:
"One pair may have several alternate aerie areas, or, as
29
appears to be true on the Colville, pairs actually breeding
from year to year· fluctuate greatly in any given region;
he~nce' there is no meaning to a static estimate of breeding
population size."
I contend that estimates of the breeding popula-
ti~n size of Gyrfalcons ha~e meaning only when applied to
!!regions" of an isolated nature and/or of large_size (such
as the Seward Peninsula). From my observations, it is
,~) . possible that the changes in cliff occupancy or the flue-
tuations in numbers of breeding pairs in areas reported in
the present Gyrfalcon literature may be relatively local
in nature. These changes probably. reflect a population.
shifi io~other·areas of a large ~egion rather than a
general non-breeding of Gyrfalcon pairs. Few authors
. . . ·~. . .r . . ·-
state whether non-br~eding Gyrfalcons were observed
attached to·nestin~ cliffs ~r if they were in the vicinity
of the cliffs. The implication is usually that they were
·_ not. Hagen ( 1952) claimed the 11 • • • existence of non-
breedines· y·ears in the life of a gyr-falcon pair. 11 and is
based on-what is, in_ my opinion, insufficient. data. Cade
,_ ...... ; . .... :; .•. :., .. ·". . ~ ... · -·.ao .. ..:,.. ----·
( 1960-)-trnP-J.ted that a Gyrfalcon pair,' if not· breeding at
(~ the sameL.ne:::?t;ing cliff each year, v1as not breecting~ .. at al·l-
I
I
I
30
---~~: .. ------------------
' ·,_ ---
that·year. Within a large region of abundant nesting sites,
th-e-possibilities of local population shifts or at least
breeding attempts in other areas would seem more reasonable
than actual non-breeding. On the Seward Peninsula during
1968-1970 only two pairs and four other individual Gyr-
falcons were observed that could h~ termed possible non-
breeders~ Further research will be· required to gain a
better u~derst~nding of_ the possible non-breeding of Gyr-
falcon pairs and how such occurrences may relate to the
population as a whole.
The theme that Gy~falcons not breeding in one
area or region may in fact breed in another area or region
/~ \_J that was· not investigated is often understated. The only
circumpolar region where there are definite indications
that Gyrfalcons actually stay in an area~ or actually
·occupy an eyrie and do not attempt to breed, is Iceland. . .
Gudmundsson (pers-. comm .-, 1969) mentioned-such observations
in th~ Lake Myvatn region. Gudmundsscn (1970) states:
. uAs the ptarmigan is the staple diet of the Gyrfalcon in
Ic~land it is not surprising that the Gyrfalcon t1u6tuates
·w±trr·the..,ptarmigan·and that ·during years-of ptarmigan
sca:rcity many Gyrfalcons do not nest at all. 11
···-
Region-wide Gyrfalcon population fluctuations
probapl_y_ ct·o, in fact, occ~1r in Alaska (and throughout~ the
_·--Gyr-falcon range)_; but· further ,study is needed to document
@ -~--~~~-.
I .
.
.
··-·---~--~-
. ~ .l
' i
'
-·
. '·
I ' .
' ;
' .
I I
I
i
.
'
' '
I I "'
f)
·, _ _}
3-l
the scope and degree of these changes in population numbers,
and to document non-breeding.
Gyrfalcon nesting cliff tenacity was low oh the
Seward Peninsuia. Of the 34 active Gyrfalcon nesting
·cliffs located in 1968 (Table 3), 18 (53 ~er ~ent) were
found inactive and unused by any species of cliff-nester
in 1969. Eight (24 per cent) were used again by breeding
Gyrfalcons. Of the remaining seven, three were occupied by
Ravens 1 two b~ .Rough-legged Hawks, one by a pair of Lesser
Canada Geese, one by an unidentified species, and one was
not checked~ In 1970, 22 (65 per c~nt) of the 1968 Gyr-
faicon. nesting clif-fs were found to be inactive. Foul"'
(12 ~~-___ ,_' .... ·----e·
}'C:J._· ~,.;o;:;uv; wer utilized by Gyrfalcons. Of the remain-·
ing eight, one was occupied by Ravens, five were occupied
by Roug}1._-legged Hawks, one by Golden Eagles, and one by an
·unidentified species. Twenty-three (48 per cent) of the 48
·active Gyrfalcon nesting cliffs located in 1969 (see Table 14) --. { ..
were found-unoccupied by any species in 1970. Fourteen
(about 30 per cent) were occupied again by ne~ting Gyr-
falcons .. Of the remaining 11, th~ee were occup~ed by
Ravens) on~·by Reugh-legged Hawks, ·one by Golden Eagles,
and .sX~ we_re not. checked. In about five to six per cent
o·f the· cas-es where the nesting ciiff vms unoccupied, the
.. . -
nests wer~_: g"one' making the· nesting cliffs at least
_ .tempo:r(lr-i;I.y_ unusable.
-·'-~~A total of 131 Gyrfalcon nestings v.rere observed
t
I
I
I
i
I
-~:-9--------------~----. - - - - - - - - - - - - - -- --32-- -- -.. - -
L·~
···._~)
Table 3. Species u_tilizing the 34 active Gyrfalcon nesting
cliffs observed on the Seward Peninsula, Alaska,
1968-1970
1968 1969 197-0.
Species Number Number Number
Gyrfalcon 34 8 4
Unoccupied 18 22
Rough-legged Hawk 2 5
Raven 3 1
Golden Eagle l
Lesser·Canada Goose· 1
Unidentified Species· 1 ,. 1
Unknown 1
Total 34 34 311
·-· . -
?./~ --~
/'\
\_~o..7)
33
Table 4: Spec~es utilizing the 48 active 1969 Gyrfalcon
nesting cliffs observed on the Seward Peninsula,
Alaska, 1968-1970
1968 1969 1970
Species Number Number Number ---
Gyrfalcon 9 14 8 14
Unoccupied 22 23
Rough-legged Hawk 11 1
-Raveri 1 3
Golden Eagle 2 1
Unidentified 1
-Unknown 10 6
Total 48 i48 }~ 8
-----=. ·d
34
over the cour~e of the study. These nestings occurred
··at 107-nesting cliffs. Seventeen nesting cliffs (16 per
cent) were involved in Gyrfalcon nestings during two
successive years (1968 and 1969, or 1969 and 1970). Only
20 (19 per cent), including the 17 mentioned above, were
utilized two out of every three years. Only four other
nesting-cliffs (four per cent) 1·1ere occupied by breeding
Gyrfalcons during all three years (1968, 1969, and 1970).
Eighty-three (about 77_ per cent) of the 107 nesting cliffs
were utilized by Gyrfalcons only one during the three
years. Twenty-seven (about 25 per cent) of the 107 nesting
cliffs were utilized once during,the three years by other
/-----.... r-- \
·--~) · cliff-nesting species. Sixteen of' these cases involved
.-.-~
Rough-legged Hawks, five involved Ra~ens, four involved
Golden Eagles, one·involved Lesser Canada Geese,,and one
involv~d an unidentified -species.
.. Most nesting cliffs had at least one and often
two (or more) alternate nest sites that had been utilized
by_ the cliff--nesting species at some time in the past. Of
the 20 h~sting cliffs ~h~re Gyrfalcon nestings occurred in
--
two out of the thr~~ years, the same nest site was occupied
iri at -least-ten cases. In the other four_instances Where
the _nestj;p_g ·cliff l'ras occupied all three years by Gyr-
falcons, _.there are a total of eight possible nest sites
(two a:t; each nesting cliff). -THo of these nest sites were-
utilized-~ll three years~ two were utilized two out of the
-.:..__. --~-~-,---·~·.
35
three years, two were utilized only once, and two were never
used.
In general, all existing nest cliffs on the
Seward Peninsula that showed signs of having had at least
one stick nest constructed on th~m sofueti~e in their his-
tory (estimated to be 400-500) had one nest site that
appeared from signs of useage to play a predominant role in
nestfngs by any of the cliff-nesting species. In subjective
terms the situation appeared to follow that of the nest site
useage observed in the sub-study area and I believe that
these predominant nest sites are involved in about 50 per
.~ cent of the nestings occurring on these nesting cliffs and
\~J'
therefore might be considered as "traditional" nest sites.
This low nest site and nesting cliff tenacity
(comoared to that attributed to Gyrfalcons and some of the
eth~~ large ~alcons [Cade, 1960]) is somewhat opposed to
the limited Alaska Range data. In one case, Gyrfalcon
pairs h~ve occupied a nesting cliff with only one nest site
for the l~st nine years and probably longer~ Prior to 1~63,
t.bis .ne.st was occasionally visited by successful egg
collectors a.r1d j.n at least t'l'lO years (Hr. Vern Seifert,
-~ pers. cornin., 1969) the pairs were shot. Cade ( 1960) dis-
cusses~ __ t.r.~:tli~tional nesting ciiffs and hm'l nesting -cliffs
-such as thi:S one may develop relatively long histories of
. -
use by ~fa} cons .
. · ~-:i__-Tt. is clear that. although the total Gyrfalcon
~--w~:
., .
I .
I
I
r
I
t I
l
l
~.--_·-_:;·"'". --
"-._
@ -~-
-
36
population p~obably remained constant the population under-
went conside~a~le shifting from area to area, nesting cliff
to nesting cliff, and nest site to nest site.
It appears that in a small area of habitat or
along a short stretch of creek Nhere nesting cliffs are
common considerable 11 cliff-shifting" occurs (i.e., the
utilization of different nesting cliffs by what may be the
Gyrfalcon pairs). It is also common for the number of
. . . . .
breeding Gyrfalcon pairs inhabiting the area to change from
year to ~ear, and for some vacated nesting cliffs to func-
tion as nesting cliffs for other large cliff-nesting
'.t spec_~.es. tha deg~e~ to which these phenomena occur may
vary locally due to changes in local prey population~,
reduction of nest sites (nests falling off of cliffs or
be~ng d~stroyed by rock-falls), creation of nest site&
(the construction of a stick nest on some cliff ledge by
Ro~gh-l~gged Hawks, Ravens, or Golden Eagles), or even the
behavior-of Gyrfalcons themselves.
This cliff shifting and alternation of nesting
··cliffs-a~d.nes~ sites probably doe~ not ~eflect the implica-
_tions of the comment made by Dementiev and Gortchakovskaya
.(i9LI5).when they stated: r'Thus it may be seen that-the
Gyrfal~on used t6 breed on the same territory constantly
. . -
ehough~ though not every successive year, having probably
been_ chased off by the Raven.!! I believe it is unlikely
that Gyr:r:alcons are "chased 11 from or forced to abandon
__---,_
i~_:)
-,__-.!-:_J"=~
j---
-,
37
nesting cliffs and nest sites by any of the three other
important species of cliff-nesters. Cade (1960) comments
on this same statement and our conclus~ons coincide. Cade
(19~0) also reports that he found a dead.uneaten Raven,
presumably killed by Gyrfalcons, below ~rt eyrie on the
Oolamnagavik River in 1956 and he mentions one other simi-
lar instance recorded j_n the literature (Brull, 1938). At
. one i96~ Gyrfalcon eyrie I found a freshly killed but_
uneaten body of a-Raven "cached il beside the nest--an
obvious .loser in some aerial encounter.
. .
Information on nesting relationships between
-~
GyrfaTcons and Ravens, Golden Eagles, Rough-legged Hav1ks, ·
arid Peregrines is summarized by Cade ( 1960). In 1968 I
observed the successful nesting of a Raven pair and a
Gyrfalcon pair on the same hillside about 300 yards apart.
In 1969 and 1970 a pair·of Ravens successfully ·nested about
100 yards Trom an active Gyrfalcon eyrie ln the ~ub-study
area. The nests were at approximately the same level and
in plain sight of one another. On one occasion in 1969, a
45~minU:te battle between the :pairs-\'Tas observed (the birds
'\tier~ unaw~_:r·e of my. presence both before and durlng the
conflict). The initial encounter was not witnessed, btit
from that. "Point on the Gyrfalcons were the aggressors. The
male Gyr:t::_alcon as initial combatant against both Ravens \'las
joined at th~ end of the first ten minutes by the female
-· ·--·~-·-"·.· .
which ha·J"-~b~en brooding eggs or nevdy hatched young at the
38
eyrie. The male immediately stepped up the force and
frequency of his attacks. The female Gyrfalcon retired to
her eyrie after 35 minutes and her mate broke off the
attack moments afterward. On many occasions one or both
of the Ravens succeeded in returning to their nest to
perch or brood the newly-hatched young and were forced to
leave the nest because of extremely powerful close oasses
by the male Gyrfalcon. The female Gyrfalcon also was
successful in driving the Ravens from their nest a few
times, but she did not put as much effort into her attacks,
often breaking off her passes before an actual encounter
occurred. However, she tended to be more vocal. The
Ravens were completely successful in avoiding actual con-
tact, ~sually by side-slipping at the last moment. At
each encounter of a Gyrfalcon and Raven, the Gyrfalcon
. presented lts feet as if to strike, while the Raven coun-
tered by rolling and presenting its feet toward the falcon
(usually while in the act of side-slipping). In two cases,
one of the Ravens actually flew upwards to meet the male
Gyrfalcon on a direct collision course, forcing the f~lcon
to flare off, but ~ithout a doubt the Gyrfalcons demon-
strated a clear advantage over the Ravens. The termination
of the aerial battle appeared to result from fatigue and
loss of interest on the part of the falcons. The Ravens
did not appear to withstand the physical demands of the
battle as-~ell as the falcons. During other observations
l . l
I
39
at this eyrie, including two three-day periods, no other
encounters or conflicts were observed between the two
species as they both attended to the feeding of their young.
From 1968 to 1970 Raven pairs nested in close proximity
(100-400 yards) to Gyrfalcon in seven instances.
no encounters between G8ldcn !~agles and Gyrfalcons
were observed, though they must occur (Cade, 1960). In
one instance Golden Eagles nested about 400 yards away from
a Gyrfalcon eyrie on the same hillside and at nearly the
same elevation. On one occasion, both Gyrfalcons were
observed to watch one of the eagles from their nesting
cliff as it soared briefly over the hill top. The nests
.,,;ere hidden fr·om each other by a small series of outcrops
and the falcon nesting cliff faced the back side of the
eagle nesting cliff.
Rough-legged Hawk encounters with Gyrfalcons were
numerous and paralleled the observations of Cade (1960).
In one instance, a male Gyrfalcon was observed stooping at
a male Rough-legged Hawk that had its nest about 200 feet
away on the same cliff. Both birds were unaware of my
presence. The conflict began when the Rough-legged Hawk;
soaring parallel to the cliff, passed directly in front of
the falcon eyrie (and about 100 feet out from it). The male
Gryfalcon was resting on a perch about 100 feet beyond his
eyrie (where his mate was brooding eggs) and as the Rough-
.c•, ---
l_ _t_t:W to intercept
lj 0
the intruder. The Rough-legged Hawk side-slipped to avoid
contact and both birds began loudly vocalizing. During the
next ten minutes t~e Rough-legged Hawk continued to circle
about on a course that brought him closer to his own nest
while the Gyrfalcon repeatedly stooned at him from above.
I was impressed with the apparent ease with which the
Rough-legged Hawk avoided the Gyrfalcon's intent stoops
by employing a combination of watchfulness, abrupt hoverin~
and side-slipping. The intensity of the battle slowed
down after about the first five minutes and continued to
do so until both birds drifterl back to their respective
portions of the cliff to perch. In another instance,
where Rough-legged Hawks nested on the same cliff and about
100 yards away in direct vtew from nesting Gyrfalcons, n1y
approach flushed a newly fledged Gyrfalcon. The young
.falcon flevJ' up the river and under the Rough-legged H<:nvk
nest (which contained five young about to fledge). Both
Rough-l~gged Hawk adultB dove on the young Gyrfalcon almost
.forcing it into the river. The .femal~ Gyrfalcon, soaring
overhead, responded immediately and nkekking, 11 stooping
hard at fhe Rough--legged-Hawks, narrowly-missing· -one
before they could continue their harassment of the young
Gyrfalcon. The Rough-legged Hawks retreated and the female
Gyr.falcon turned her attention to.me.
Duri~g the course of the study, Rough-legged
Hawks are ~nown to have shared the same cliff with Gyr-
falcons in at least nine instances. The nroximity of the
nests varied frorn 200 feet in one case to about 400 yards.
Many· additional ca~~s existed in which Rough-legged Hawks
nested on another, often smaller outcrop, within 200 to
400 yards from active Gyrfalcon nesting cliffs.
Food Habits
No attempt is made in this paper to condense the
circumpolar data pertaining to species known to have been
killed by Gyrf~lcons. Hagen (1952) and Cade (1960) have
already summarized a considerable portion of this informa-
tion; those and three other papers (Murie, 1946; Dcmentiev
and Go::-'tchakovskaya, 191!5; and Bengtson, 1971) are of rn·i--
mary importance because they involve: (1) reasonably larsc
sample sizes; (2) observations over more than one year 1 s
time; and/or (3) ojse~vations at more than one eyrie.
The general characterist:cs of Gyrfalcon diets,
based on these papers, can be summarized into the followjng
points:
l. Gyrfalcons rely heavily on resident species
of birds and mammals in the Arctic and subarctic.
a. Gyrfalcons prey heavily on V!illow rtarmi·-
_._.,_·
Ptarmi~an-ean be considered as the single ~ost important
food item· (Cade, 1960; Hagen, 1952; Bengtson, 1971) on a
circumpol~r basis.
42
b. Small mammals are known to be an important
food source on a weight basis in Alaska (Murie, 1946; Cade,
1960). The Arctic Ground Squirrel is particularly important
and can surpass ptarmigan as the most utilized food species
in some areas of Alaska (Murie, 1946; Cade, 1960). The
lemmings (Lemmus lemmus, the Norwegian Lemming, !::·
trimucrona tus, the Brovm Lemndng, and Di_cro~C2.!_1Y x £_;roen-
landicus, the ColJared Lemming) on a Horld wide basis see:n
to play more variable roles and usually are not as imnor-
tant as food (Dementiev and Gortchakovskaya, 1945; Hagen,
1952; Cade, 1960). In J\L1sJ~a the Hro1·m Lemming, the
Collared Lemming, the Tundra Vole (Microtus o~conomus),
the Singing Vole (~. miurus), ·anrl the Red-backed Vole
(91ethr_~_C?_r:!?mV~ rutilus) appear to play an important but
indirect role in relation to Gyrfalcon fooc<. habits ( Cade,
1960). Large numbers of microtines commonly a.ttract laqr,e
numbers of rodent-eating birds, many of which are utilized
by Gyrfalcons for food probably in greater proportion (at
least by weight) than the microtines themselves.
2. In Iceland a relatively stable and large
population of ducks is heavily utilized as an important
source of food by Gyrfalcons nestin8 in, or frequenting,
the Myv_a:tn area. Utilization of Rock Ptarmigan increased
as the ptarmigan population increased suggesting a prefer-
ence for this food species over the ducks (Bengtson, 1971).
lj 3
Salomonsen (1951) considers waterfowl to be one of two
principal ~ources of food to Gyrfalcons during the nesting
season in Greenland.
3. Dementiev and Gortchakovskaya (1945) docu-
mented a high utilization of seabirds (Alcids, LariJs,
and Anatids) by Gyrfalcons nesting near seabird colonies
on Kharlov Island. Salomonsen (1951) considers seabirds to
be a principal source of food for nesting Gyrfalcons in
Greenland and indicates that Gyrfalcons usually nest near
seabird colonies.
4. Gyrfalcons, on a circumpolar basis, take a
relatively wide range of prey other than the species listed
above, ranging from smaJl passerines to other raptors.
Gyrfalcons, however, tend to take a narrower range (in terms
of numbers of species) of prey than rto Peregrine Falcons
(Falc~~ per_Qr;rinus) (Cade, 1960).
·5: In general, it appears that Gyrfalcons rely
principally on two or three prey species as a source of
food (Cade, 1960), and that coastal-nesting pairs feed
chiefly on Alcids, Larids, and Anatids while inland-nesting
bir~s feed chiefly on ptarmigan and sDall mammals
(Dementiev. and Gortchakovskaya, 19115; Cade, 1960) ._
6. Gyrfalcons also appear to be opportunistic,
capable of taking a wide range of sizes of prey, and are
able to shift to other food sources when ptarmigan become
scarce (Bengtson, 1971; Cade, 1960).
411
7. In some parts of the world Gyrfal.cons probably
fluctuate with ptarmigan cycles (G11dmundsson, 1970) and in
some instances appear to breed in lower numbers in response
to ptarmigan lows. The degree of this relationship to
ptarmigan poptllations probably varies from region to region
and is poorly understood. Fluctuations of Gyrfalcon numbers
have been reported by Salomonsen (1951) in connection with
lemming nur:1bers in Northeast Greenland.
Prey utilization on the Seward Peninsula
During the course of this study a total of 1,1133
Gyrfalcon kills were identified from the immediate area
around ~0 Gyrfalcon nestings (see ~able 5). Avia~ snec10s
constituted 85 per cent by nurher and approximately 87 oer
cent by weight·of the total kill. Mammalian species consti-
tuted the remaininr.; 15 per cer..t by number and 13 per cent
by weight of the prey remains (see Table 6). Cade (1960)
reports lower mammal subtotals for ten Colville River
eyries (13.6 per cent of total/6.6 per cent of total/1.2
per cent by weight based on 142 kills), but a much higher
mammal subtotal (76.2 per cent of total/80.1 per cent by
weight based on 429 kills) for three Alaska Ran~e eyries
(data obtained from Murie, 1946, and unpublished; M. W .
. Nelson; and J. H. Doyle). This marked difference in the
proportion of mammal remains can be attributed almost
entirely to the differences in frequency of occurrence of
Table 5. Collection dates of Gyrf::tlcon jlrcy rer~ains
J-:yrj_£
1
.2
3
5
8
9
10
17
18
19
Total eyries
2
3
4
5
6
7
8
12 ,c
.LU
20
21
22
23 2
Vern-69-1
Total eyries
1
2
5
9
11
12
13
14
15
16
21
24
25
26
27
28
Total _ey:ries
'I.'otal eyries
Total nest-:l,r.gs
Year
1968
1968
1968
1968
1968
1968
1968
1968
1968
1968
10
1969
1969
1969
1969
1969
1969
1969
1969
1969
1969
1969
1969
1969
1969
14
1970
1970
1970
1970
1970
1970
1970
197'0
1970
1970
1970
1970
1970
1970
1970
1970
16
29
= 40
22 June; 16 Aur,ust
6 June; 11 July
16 June; 6 July; 23 August
4, 9, 14, 25 June; 5, 23 July
21 July
31 Nay; 9 July ·
9, 14, 23 Jun0; 6 July
13 June; 12 July
21 June
19 July
Number of visits = 24
19 June; 3, 13 July; 12 August
211 May; 16, 23, 24 June; ·r, 11,
17 July
20 July
16 June
21, 26 June; 8, 12 July; 5 August
11 Aup;ust
13 June
5, 13 July
27 r~ray
13 June
13 June
20 June
16 July
July (date unknown)
Number of visits ~ 26
25 July
1 June; 1 July
29 Nay; 4 June
8 June
7, 8, 13, 14 July
6 June; 7, 8, 13 July
27 July
28 May; 20 June
24, 25 June -
31 May; 5, 12, 22, 27 June;
9 July
26 July
23 June
August
15 July
15 June
27 July
Number of visits = 29
Grand total number of visits = 79
lNot included in the total.
2This cy~±~ ~as located by Mr. Vern Seifert, who collected
~;hat remains he could find for donation to this project.
T:tbl~ 6. Tot-:\1 106~-1070 Cyrrnlcon food reM~iM
TOTAL BIRDS
Aretie Ground Squ1r~~~ (Sae~~on~!1us un8ul2tu~)
Collar~d I,ei..rn1ng Cp!.::-~stc~-'X.. z.ot~~}j.;o.~1co.:s)
Unlct~nt1t1ed le~n1c.~>
Drown Lcl""' . .'lling ((.l:' .... r.,u-: t:"'!mucronntu:~)
Un1dent1r1ed voi::?s--• --
Red-bac~ed '/ole (r.le~:-"_-:onor."-;5 r'•tilus)
Un1dent1fled r.ic~o~ices ---
Tundra Vole _q~t-:~ :--"'~2.!!2~)
Short-tailed ~:cas~l (:--·-.::.tel3. cr!"lin~a)
Mink (~~~ y~) --------------
TO:JJ. I·'J,X.':t.LS
Un1dent1t1ed kills
"'l'OTAL KILLS
Total categories -49
1'ote1 identified op~~:-< • -39 (31 ev1en, 8 r.:ammal)
'l'ot~l miri1mun spcc1eo ""-~0 (32 av!a:'l, 8 roa"'-"'al)
"'Oata rrom Cade, 196C
~·ota1
~
876
155
30
29
23
1~
1~
13
12
11
11
8
7
7
6
5
5
lj
3
3
3
2
2
2
2
1
1
1
1
1
1
1
l
1
1
1
1
~
1,260
170
24
8
6
5
~4
2
1
1
_!.
262
_!
1,~83
Pe!> cent
~--~
59.1
10.5
2.0
1.5
1.6
0.9
0.9
0.9 o.a
0.7
0.7
0.5
0.5
0.5
o.~
0.3
0.3
0.3
0.2
0.2
0.2
0.1
0.1
0.1
0.1
0.1
83.5
llS
1.6
0.5
0,4
0.3
0,3
0.1
0.1
0.1
1~.9
.Jl.d
100.0 ! .02
r(\'r ~<""nt
F!r:1-···:1:-~
6'l.5
12.3
2.4
2.3
1.8
1.1
1.1
1.0
l.O
0.3
0.9
0.6
0.6
0,6
0.5
0.4
0.4
0.3
0,2
0.2
Ow2
0.2
0.2
0.2
0.2
0.1
--
97.6
61.1
l0.8
3.6
2.7
2.3
16.8
0.9 o.s o.s
107.7
A~pl•c-rr1.J:te rc r· cent
\-H'h"':ht cl:tss or tot.1l
!!l.L:::"':.~-~ !,:;. W~1,•M
•<so 71.6
·3~0 7.4
'135 0.6 • 30 0.1
100 0.2
380 o.s
100 ~.2
·~ao 0 -,
370 0.6
Sc 0.1 sco C.1
1 90ii 0.9
tOO 0.6
275 0.3 •goo 0.7
§ 30 0.1
500 0.3
320 0.1
500 0.2
30 0.1
110 0.1
12 0.1
17 0.1
35 0.1
1.~50 0,2
300 O.l
45 C'.l
O.l
100 O.l
" 30 0.1 .. .-.... -0.1 -.;JU
200 O.l
200 0.1
).0 0.1
HO 0.1
20 0.1
---.12 .. ~: .. .!.
86.9
•soo 1"2. 6
50 o.a so 0.1
50 0.1
30 0.1
30 0.1
30 0.1 •o 0.1
200 0.1
ill _Qd
12.9
lCO.O
the Arctic Ground Squirrel in the prey remains reported for
these different regions, and probably reflects this species'
.
availability at the times the.data were collected.
On the Seward Peninsula, three categories of
prey stand out as major sources of food to the Gyrfalcons,
both by number and weight (see Table 6). These Dajor prey
species are shown separately in ~able 7. Ptarmigan clearly
appear as the primary prey. Though no attempt was made to
separate the two species (~. laGonus and~· mutus), it is
known that both were taken. Ptarmigan co~prised 59.1 ner
cent of the total prey reJ'lains ancl 71. G per cent by body
weight. That the various species of ptarmigan form a major
portion of Gyrfalcon prey throughout the Gyrfalcon's cir-
cumpolar distribution is generally well known (Dementiev
and Gortchakovskaya, 1945; Hagen, 1952; Cade, 1960; Drown
and_Amadon, 1968; White and Weeden, 1966; Ben~tson, 1971).
Ca.de._ .(1960) noted a preference 1'even in a year when they
(i.e., ptarmigan) vv-ere scarce!! from his Colville River data.
Hagen (1952) comments on this preference when microtines
were abundant and available to Gyrfalcons in Dovre, Norway,
and Bengtson (1971) states that in the Myvatn area of Ice-
land, trptarmigan, when abundant, a1'e the preferr.ed prey even
in areas containing. excellent habitat for vraterfov.rl. :r
Bengtson -(1971) reports an interesting increase in pta~migart
utiliiation by Gyrfalcons as otarmi~an increased in numbers
I
. I
'l'ab1<: .7.. 'l'h~ ttlr<::e maJor Gyrfalcon food items
Per cent Per cent
~ Humber 1968 Total flircl->•:a;:~mal
?tarnica~ \!911 G4.~ 7~.8
Ground :;quirrels 43 9.4 68 .'3
Long-tailed Jae~.;ers 42 ...2.:2 lCi. 7
TOTAL 379 83.1
Per cent 1968-1970
?tar~.1JO;an 876 59.1 69.5
Grour.t'J ::;gu1rreln 170 11.5 76.6
I,rmr:-tn11crl Jaer:crs l~ ~ l1.:J.
T0'1't\r1 1,201 ill.O
Per cent Per cent
~~ 1969 Tot't1 B1 rd-!·lammal
lit] 48.6 62.7
63 21.11 95.5
.Ji ..2.:.!!. ...1...:.!2.
222 75.4
Numt>er
439
64
-21.
600
Per cent
1970 Total
59·9
8.7
l.U
81.8
Per cent
Bi:--d-~!3:7.l~al
63.7
63.8
15.2
~:ote: \.lillow Ptr.trm1p;:tn <k· laro:ous) and Rock Pt!lrnir.;an (J.. r:111tu0) ~:ere concl.dcrcd as one category. Xo attcm~t was
made to separate these two species. Three additional jaer,cr kills could not be identified to specie5, but
were probnbly Lnng-tailcd Jae~crs (~. lonricnuclu!)• A fourth kill was n Pnras!tic Jaeger(~. pnrn~ttleus).
CJ
in an :=trea whe·re thous:=tnds of cluc-ks forr.1ed a readily
available and heavily utilized fc6d ~ource.
lj 9
It appears that these observations of ptarmigan
"preference" are generally valid. Such a nreference for
ptarmigan by hunting Gyrfalcons seems logical and expected
for an avian predator that is almost completely dependent
upon them for about two-thirds of the year. From the
extensive literature of falconry, it is generally known
that trained falcons and hawks can readily develop specific
interests in a particular prey species or type. Although
almost no data are available to axnlain what young Gyr-
falcons do during the winter months, it is probable that
they too are strongly dependent upon ptarmigan for food as
winter sets in. It seems likely that ptarmigan are strongly
fixed as a nprey imagen in Gyrfalcons; that this occurs
early in the life of a Gyrfalcon; and that the i'preference :I
could be. termed one of necessity.
Cada (1960) reported that ''On the arctic ~lope
ptarmigan usuallymake up nearly 90 ner cent by weight of
the total consumed. 11 Certainly the hir;h availabili.ty of
Long~t~iled Jaegers and Arctic Ground Squirrels on the
Seward Peninsula accounts for a large portion of the approx-·
imately l8_per cent difference between Cade's data and nine.
Arctic Ground Squirrels were the second most fre-
quently ·bbdu~rfng prey species in the Seward Peninsula prey
.t'ema:Lns . (see '.L'ab le 7) and compr'i sed about 13 per cent by
50
weight of the total Gyrfalcon prey remains (see Table 6).
Cade (1960) re~orded only six eround squirrels constituting
abou~ 5.8 per cent of the total prey remains and about six
per cent by weight from ten Gyrfalcon eyries on the Colville
River in 1959. Eieht arctic slope eyries where prey remains
were picked up from 1952-1957 produced only one ground
squirrel which contributed a small 0.7 per cent by number
and 0.8 per cent by body weight of the total prey remains.
Murie 1 s (1946, unpublished) Alaska Range datfi (reported in
Cade, 1960) from three eyries reports 259 ground squirrels
totalling 60.5 per cent by number and 78.9 per cent by
weight of the total orey remains. One Sheenjek River eyr;e
visited by George B. Schaller (reported in Cade, 1960) pro-
three of which were ground squirrels. In
my opinion these differences in ground squirrel useage are
due to differences in their availability to Gyrfalcons at
the times and places these collections were made.
Cade's (1960) comment that "Gyrfalcons are much
more specialized than peregrine falcons, Falco peregrinus,
on a pop~lation-wide basis in-their food habits~ depending
primarily upon one or tHo resident species of prey, !I is
supported by the fact that ptarmigan and Arctic Ground
Squirrels accounted for 1,046 (about 70 per cent) of my
total li483 identified Gyrfalcon kills. By body weight
these resident species (Willow Ptarmigan, Rock Ptarmigan,
and J\.rctic Ground Squirrels) comprise about 81! per cent of
J
I
51
the total biomass (see Table 6). Cade (1960) found a
comparable situation when he analyzed Murie's Alaska Range
data and his own Arctic slope and Colville River data. Of
the three data sets, Cade found ground squirrels oredominant
in the Alaska Range data and ptarDigan predominant in the
Arctic slope and the Colville River data. My own observa-
tions indicate that Gyrfalcons in the Alaska Range do indeed
take large numbers of ground squirrels.
Ground squirrels, unavailable to Gyrfalcons from
about 1 October to 1 May, contributed almost twice the bio-
mass on a Height basis than Long-tailed Jaee;ers cUd in the
summer on the Seward Peninsula. However, it should be made
clear that Gyrfalcons do not normally consume the digestive
tract of ground squirrels and this portion plus the heaviet>
mammalian bones constitute a relatively large percentage of
the weight of this species. Conversely, Gyrfalcons often
appea~ to con~u~6 the digestive tracts of jaegers and this
probably results in a more equal ratio of consumed biomass
for these two important species. Two caotj.ve birds were
also observed to follm'l this feeding nhabi t.,
Long-tailed Jaegers were the third most frequently
occurring prey species in the Seward Peninsula Gyrfalcon
prey rem~!ns (see Table 6 and Table· 7). This species
accounted for 10~5 per cent by number an~ 7.4 per cent by
vleight of the t-otal prey remains. On a 1vei~ht basis all
jaegers 6bmbined (Long-tailed Jaegers, Parasitic Jaegers
':'.l!~.:le 8. 'rotal ~1~r:;.to~y 't!.rd !!p~cieo 'lC.entific<! !'ror-:. th~ 1968-1970 ()j'rfalcon p:-cy rc:nri1n5 anc': 11:;;':-ed in Vtt.:'"i("'U3
f~r:-o~t~nt ~;roui)~
----~--------------~·~-~~
Chnr<Jh1rd!l
~n~~~~dn c~ncltJ~1n~
jcc~cr= ~nd rJucko)
Un11~~t1f1cd n1~rato~y
t.! rd ::pp.
159
79
12
58
30
?c:" cc~t of
totnl %ill_
0.8
2.0
25.5
-------·~---·-· ----------
l'c:-cl!nt by
·(rc~~.ht of
tc~~:l~~
2.2
0.5
0.~
17.6
fer ccr.t. c!'
t'>t::t1 :::1.o;r~:tory
~ :-~.1,_!1'-----
20.6
7.3
F~r c~r:.~ tly
w~~ir:ht of ~~~.:'ll
::.1._i;o.~":<':_::' ~:'..:-d :~-:.1 ~
12.5
!;.6
2.2 '
18.3
99.9
'~ '-''
[\)
53
[0._. parasi_ticus], and three unidentified Stercorarius spp.)
accounted for about 7.5 per cent of the total biomass. Cnde
(1960) recorded only three Long-tailed Jaegers in his Col-
ville data and two Parasitic Jaegers from his Arctic slope
data. White and Springer (1965) reported only one Long-
tailed Jaeger from among 38 kills they identified from a
Gyrfalcon eyrie near Hooper Bay, Alaska. It is possible
that the Sevrard Peninsula, juttim~ out into the Bering S.::a
i~ a more desirable jaeger habitat.
It c .. r)pears that large lernuinr;-vole por,ula.t ic)11s
influ~nce Gyrfalcon utilization of some nigratory avian
species,. notably Long-tailed Jaegers, Short-eared Owls
legged Hawks, since the availability of these species to
Gyrfalcons depends strongly on the presence of microtines.
Cacle (1960) states that nThe sit:;nificant fact for the
gyrfalcons on the Colville was not their predation on
microtines, but the presence of rodent-eating birds which
had -be-en drawn into the region-by -the microt ines. :r Cade
found that "on a weight basis more than 20 per cent of the
1959 sample of gyrfalcon food consists of rodent-eating
birds." Of the total 1,483 Gyrfalcon ld1ls i_dentLfied from
the Seward Peninsula, 171 or about 11.5 per cent were rodent-
eatinp; birds (j <w_gers and Short-eClred Owls). On a wei13:ht
basis this food source totaled about 8.3 per cent of the
biomass (see Table 8). 'l'hes-e dat-a :1ppear to indicate th~lt
this food source is important to Gyrfalcons whenever it ls
availible to them.
Cade (1960) found the.t ~he S'~_;:·,p·ei' foods of Gyr-
falcons in Alaska characteristically contained two or three
species that contributed "more t~12.n 70 pPrcent of the total
sample. 11 From the literature, it appears that thj s car; be
considered a general circumpolar characteristic of Gyr-
falcons, and that it is not unusual for the percentage to
become as high as 90 ner cent in certain regions 1f we con-
sider ducl{S i.n general as one cater;ory of 1Jrey (Sen[!tson,
1971). My data agree with this ~eneralization and with
Cade's statement. In order of occurrence (see Table 6),
ptarmigan, Arctic Ground Squirrels, and Long-tailed Jaegers
constituted about 81 per cent (1,201 kills) of the total
1,483 Gyrfalcon kills from the Seward Peninsula. By body
weight, this small group of species, including three resi-
dent species, accounted for nearly 92 per cent of the total
biomass. The remaining prey species constitute a small
propo~tlcin of the total prey remains and are generally com-
parable-to the data of others (e.g., f'-1urie, 194 6; Hagen,
1952; Cad~, 1960; Bengtson, 1971). Cade (1960) states in
reference to Gyrfalcons that, J!In Alaska the data on food
-hab~ts of interior populations support the conclusion of
Dementiev and Gortchakovskaya (1?45) that gyrfalcons, i11
distinction from peregrines, are primarily oriented toward
predation on permanently resident arctic species of prey
whereas peregrines prey on migratory species.11 IV!y data
further support the fact that Gyrfalcons do indeed prey
heavily on permanent resident specie~, particularly those
Gyrfalcons nesting at some point removed from an actual
coastline but that these resident species play an important
part in the food habits of Gyrfalcons more closely asso-
ciated with the coast.
The occurrence of one Mink (Mustela vison) in
1968 must be considered unusual. This mammal is a rare
species over the western portion of the Seward Peninsula
(John Burns, pers. comm., 1968), and it is doubtful that
Mink are often in a position in which Gyrfalcons may take
them. The occurrence of one Short-tailed \{easel (Mus~ela
erminea)-in 1970 is also unusual, thout;h this specie·s is
_fairly common on the Seward Peninsula particularly in high
lemming years, and is often observed hunting on the open.
tundra where it is exposed to aerial attack. Dementiev and
Gortchakovskaya (1945) identified the only other specimen
of this species reported in the GyrfaJ con literature fro:n
an eyri~ on Kharlov Island.
The role of migratory birds in the food of Seward
Peninsula Gyrfalcons is of considerable intrinsic interest
since it is ~his component that lends the majority of di~er-
sity to the spectrum of prey taken. The migratory species
have been divided into various grouos for comparative pur-
poses. As a whole, migratory species comprised about 26 per
cent by number and approximately 10 oer cent by weizht of
the total prey remains. These data indlcate that Gyrfalcons
do take a significantly smaller r~orortion of migratory
species than arctic peregrines tend to take (based in part
on Cade's 1960 data). It is interesting, in addition, that
this food source is of a large enouch size to serve as a
relatively steady and probably significant source of pesti-
cide and PCB (polychlorinated biphenyl compounds) contami-
nation to Gyrfalcons if in fact these migratory species are
contaminated themselves.1
It is interesting to compare Cade's (1960) Arctic
slope and Colville River data with my total list of orey
species (s~e Table 6). By combining his data with that of
Murie (1946, unpublished), Cade (1960) summarized most or
the available Alaskan information on the summer food haJits
of Gyrfalcons. These combined Gyrfalcon data contain
'' .. ~ohly twenty-one species of prey as compared to fifty-
seven species that are Us ted for peregrines. . . '' ( Cade,
.1960). Three of these 21 categories are comprised of uniden-
tified ducks·, 'un-identified passerj_nes and vole species that
_ 1 Prel:Lminary inves ticat :Lons by I:Jayr::an E. vialker, University
-of Alaskay indicate that all specimens of Gyrfalcon prey
specie,s -t~Ollected_ in 1970 analy2~d so far co:1tained detect-
able levels of both chlorinated hydrocarbons and PBC. This
study ·will be published separately.
57
may or may not have been different from those similar
species listed. The arctic slope data for 1952-1957 com-
prise a total 6f 142 kills collected from eight eyries, and.
consist of only 12 categories includin~ unknown vole spe-
cies and unidentified ducks. A similar situation exists
with the Colville data--103 kills consisting of 11 cate-
gories of prey species including that of unidentified
passerines. Murie's Alaska Range data (reported in Cade,
1960) are even less diverse--429 kills consisting of seven
categories of prey species including a known total of at
least six species. My data for the Seward Peninsula, pre-
sented in Table 6, list a total minimum of 32 avian and
eight mammalian species.
Cade (1960) stated that, orr have had to utilize
pellet analysis to a great extent because of the infrequency
with which other types of remains have been found at most
of the aeries during the time of my visits. n In my expel"-
ience it is unusual not to find numerous skeletal material
with attached feathers or fur in or below eyries .. Since
Cade was primarily studying eyrie.s situated on river cliffs,.
river break-up and changes in l'later levels may explain his
difficulty in finding prey remains. The striking differences
between cade's (1960) data and mine may reflect: ( 1) a
difference in d~versity and availability of prey·species
betwee~~he regions (i.e., at the time of study) and (2)
a difference in sample sizes. It is possible to extract a
58
number of combinations of eyrie collections (see Tables J2a,b
to 27a,b) from my data that will construct data sets of
similar numbers of eyries and numbers of kills and thus give
results comparable to the low diversity of species found by
Cade.
Bengtson's (1971) Icelandic data are more compar-
able to mine. He lists 24 identified avian soecies (ll of
which are duck species) and three a~ditional prey catecories
(Anas spn., untdentified dudes, ~mi :::;;--1:111 ducklings) from a
region lacking small mammals. The data that best compare
with mine are those of White and Sprin~er (1965). Their
data are from only one Gyrfalcon eyrie near Hooper Bay,
Alaska, and consist of 38 kills collected in a brief 15-day
segment of time during the Gyrfalcons' nesting period.
White and Springer (1965) list 18 categories involving 2
minimum of 14 spec~es. Eleven (28.9 per cent) of the total
kills were shorebirds, nine (23.8 per .cent) were ntarmisan,
six (15.7 per cent) were Larids, six (15.7 per cent) were
passerines, and four (10.5 per cent) were Anatids. While
Cade's (1960) data n ••• pertain mostly to eyries in the
more inland tundra and mountainous ar·eas. n (as stated
by White_and Sprihger, 1965), my data and that of White
and Springer (1965) are from coastal areas or peninsular
areas strongly influenced by the coast.
Yearly va-riations in prey utilization
Gyrfalcon prey re~ains from the Seward Peninsula
':rere segregated by year and the yearly compositions of the
1968-1970 prey remain~ are listed in ~able 9. In attemot~
ing to compare the 1968, 1969, and 1970 collections, con-
sidcration must be given to: (1) the consistency of the
search effort; (2) the consistency of the tir.dng of the
collection visits; (3) the nunbe:t' of eyries visited dur>ir.g
each year; and ( i!) the chanp:es in orey soecies numbers and
their availability to Gyrfalcons.
1. Search effort: SeClTch effort '.-Jas generally
consistent throu,c:;hcut· the study. f~o1;1ever,_ in 1969, ~3om~
nests were not climbed to ti1ough they were visually observed
from close range. Such nests were not climbed to because
they appeared essentially devoid of prey remains. In l9[q
mor>e effort via.s DX!Wnded in search belm·v-ncstinc; cliffs and
at nearby perching: places. For unknm,m reasons, pre:,r remains
were scarcer both in the nests and below them in 1969. Dur-
ing that year only· 2911 kills i'Jere collected--a much lower
figure compared to those of 1968 Rnd 19'70 • ·· · "
--2 .. --'l'iminp; of visits: During 19GB, visits to
Gyrfalcon eyries were spread fa5rly evenly over the period
31 f.[ay-tcr-·23 July. In 1969, the uajor'ity of the visits
occurred between 15 June anrl 20 July. It is oossihle that
some remains, accumulated prior to 15 June, were scattered
and thus unrecoverable. In 1970, v~sits corresponded
60
closely with those of 1968, occurring evenly over the
period 28 May to 27 July.
3. Number of eyri~_s visited: In 1968, ten
Gyrfalcon eyries were visited to collect prey remains and
pellets~ In 1969, 14 eyries were visited, representing an
increase of 30 per cent in the eyrie sample size over that
of 1968. In 1970, 16 eyries were visited, representing an
increase of 60 per cent in the eyrie samole size over thnt
of 1968 and 33 per cent over 1969.
li. Prey __ abundal]_ce and avai lability: Prey
~pecies' numbers changed markedly in some instances from
T9GB to-j_970 .. ~The scope of this study did not permit
detailed censu~ of pPey species, but general day to day
observations were made and are discussed later.
It is evident from Table 9 that ptarmigan, ground
squirrels, and Long-tailed Jaegers stand out both by nuJ'1her
and weight as the Ilro~inent prey species durin~ each summer
(also see Table 7). It is significant that, by weight,
these three prey categories together comprised 92.4 per cent,
85~~ ~er c~nt, and 93.5 pe~ cent, respectively, of the 1968,
1969, and 1970 prey remains. It is also interesting to note
that the -two avian categories· (ptarmigan and Long-tailed
Jaeger~~ tbgether accounted for a large proportiori (82.3,
-_.o---
62.0, and 83.7 per cent, respectively) by weight of the
yearly total kills,. and a very large proportion by Vleight
(92.6, 80.9, and 93.5 per ce~t, respectively) of the avian
species taken. By comparison, ground squirrels constituted
a relati~ely ~mall, though obviously important, segment of
the yearly t6tal kill by weieht (10.1, 23.3, and 9.8 per
cent,-rer;pectively), but comprise .q very large portion (93 .I~,
99.5, and 95.7 per cent, respectively) by wejght of the
yearly Mammal kill. Further, it is note-worthy that the
tvw major resident specles' categories (ptarmir:;an and
ground squirrels} together ·by ~'Ieight co-nstlb.i'ted a large
and relativeli stable portion (86.1, 81.5, and 84.0 per
cent, respectivcily) of the yearly total kill. The remainder
of tile yearly 'prey remains consisted primarily of small
numbers of a variety ~f migratory bird species and micro-
tines, and constituted a relatively small portion by weight
(7.6, 14.7, and 6.5 per cent, respectively) each summer of
the yearly total kill. During each summer of the study,
Gyrfalcons on the :3e\·Jard Peninsula took a significant pro-
por>t ion o-f·-migra tory bird species. These l'la:ta are presented
in 'l'able 10. -It should be emphasized, in vie~.., of potential ·
pestici-de and -PCB contamination, that a relatively large
proportion of these migrat.u1·y blrds are top level consumers
in their own right.
The yearly data generally follow.the overall data
from the £eward Peninsula listed in Table 6 and pTeviously
discusse~ in this paper. In seneral, the same conclusions
as those obtained from the' data ln rrable 6 could be drawn
from any nne year's data. The most interesting aspects of
62
~·r,ble 9. I ~63-1 ~i ~ C:;rfslcoiJ rood rf!o:--e ~ n~ CC1ipUt('d 0:1 • yculy bo.~',
.. ------------~---------------~-------~· .... -........ _... .. _..-.....--_ ....... ~-------
--·--J~~~------------____ l.c_~---~-------___ _:1_ .. !1. ('!._ ___ -------------
~·ot> l Per C't" r\''~ r:""r c l nt 'r~tlll Per ce:".t ;\·:· .-r: :·t 7c!:.ll :e~ CCI'.~ !(':' .'let.
r.llls £L~.f.l f<. ~ '!" -~-... '! :--.'ll !!._11 ~ ~ t~ '"-~ r:_t_:-.::~:.·:_·.21. f_!];~ f'_::._~t~l_ ~~.:-.:~: ... :~:..:~.:~:_
?tt~r=.1 r::~n !jJt·~!(':S 29b 6~. 5 74.8 1~3 ~3. (, C?.7 bJ9 ~9-9 (.::. 7
!.onr.--t.1llf'.! ;; .7!t ~-.er ~2 9.2 10.7 16 5.b ; .~ 97 13 -~ 4.~.2
J.r:;crie.:~.-, G~-l::c~ .~ l "': ·.·~:· ~ 0.9 l.O 11 3. 7 ~.E 15 ~.n ?~3
Un1CI!'ht~!"1t".j r·•-~~-~:--lne 5 1.1 1.3 3 2.7 3.~ 16 2.~ 2 .. 5
l'nl~c~.t! !'! cd bi: -:~ 5 l.l 1.3 ;> 0.7 o.~ 1(. 2.9 i. 5
v~~'(ac-nt1~!ed s~,)P:t ~r'\.!.:S 3 0.7 o.e 5 1.7 ;<,.2 6 o.o 0.9
!'-l~<'%-)~f""e:1 l\ 1 t t 1w::~.c 3 0. 7 0.8 11 J. :· l.7
Cc;;":.ou ~r.! re 7 1.5 l.S 6 o.e o.~
St'J."Jrt-~<·:-e-1 c~l 6 1.5 2.0 2 0.7 0.9 2 0.3 ~. 3
\.";1!::~·r-cl ~ 0.9 1.0 2 0.7 0~9 5 0./ O.R
F.o~:.1a l 0.2 0.3 8 2.7 3.S 2 (1.~ 0.3
0:1!ci,:ont!ntd ... &.tcr!'c\11 l 0.2 0.3 3 1.0 1.3 ~ 1).5 o.G
F! .~t:t 11 3 0.7 o.e 3 l.O 1.3 l C·.l 0.2
'!'.; rt.t":.: h:l~ln 7 2.-3.1.
'£'.:,r-t.?.~ >:.j. Goo ... 1 t 0.1 0.8 3 (•.~ 0.5
O}.r.:-q•..-:.1.." ~
1.-
l.3 1 ').l 0.2
L:,p~ ;..";.i J.(l.~f: ~-i ..l':" l 0,2 0.3 2 0.7 C.9 2 t·.:. 0.3 r i ~~·cr. G ::J.:.!"··. ::. il l.~ !.f.
u~ .... :!~c-&:t~ rJ .. r;J s?·;:e-=-~ ·-2 o .. ~ o.r; l 0.1 0.2
~:-.1:>::r~t~!2.:.-~ <! 1::-!r.:-3 0.7 0.6
Cor r.y-C ~;co:-~:"-.~ ·::~~'-' l~: 1.0 1.3
1.11-::<!t 'i\:;:. ~ ~:: t:r '= 0.2 (1.3 1 C.l 0.2
~-C'.r! r-_:>]1 !. ~;('..:'! "·' 2 0.7 0.9
":.;·::.' ~ . ._, ..• r ~ ,.;: 1 0.3 (, .. ~ (· ·'-C.?.
~nc-u r. ·; .~. f, ~ ~' .. <: f"J..) ? . ~ };) ~~;k fc'.CO 1 (..). VoL
c~·t r:l:··• 1 n ._,. '! ·:, \l (!.~ 0.3
St:!:l!f-!··c-.?.t·.::! f~r--~~~ l 0.3 0~ ,.l
it.'er.d~r ~:-_:.-:'.t ~:-.lE:t" o.:-o;3 .. - -~· . . . C.l c.~ .l•t";:! :'>~1 11:: .;..'l,.'•'lt:t· ~
tia~ J! 1::1 r! :..·-: ::·.:·:1r:.f~~;-., 1 c.; 0.3
Patasllic: . :. -~ ~· .·.•.• ;-1 O.l. 0.~
P.:: rr~:·:·( ~ t:.;:; , .. , 1 c-., (\.~
Unhh:.u.r:(d Ol~ll~ ts 0.3 o.~
~ ..... -~·o;.·~·-· 1 (\.l. o.,'
\'z..:-JcJ ·::,;-·.t:'ih 1 (J.l 0.2
a·.j.t.(.;· 1': Co 1 ~ 1 0.! ':.1.2'
Fot sr·~:-;·.:.k __ l_ _;:.~_, _ -..c.~?
'i"(fJ"}.!,.. ~It:>~ 393 SG.~ lCO.O ~2e 77 .(. 10/).': 639 e-: .2 !(('. ~
l••ct! • Cl't';;··•l g~1 .1 J .... ~el ~l >"·.( 6~.) 0 ~] ·' S5.5 (; L1 ,-'I .· ... ·.
Collel'c'.i I ,_··:::r'b 11 :t.l! !'( .s 3 1.0 ~.t lO 1.( 1.) ,,
Ur.l~.!nl! ~ ' . ..:j ! I';~.:'!!;;~;~. ~ 1.1 t.~
r.ro~:l Lt:::.:-.1 ~~.:; 5 l.l 7.9 1 ~·.1 C.2
VnJ-:\('nl;! r: :--1 V\•1(·~ 1 ·o.2 1.6 • C.5 t.)
f.'!d-t.a~i:cJ -IC:l-l' ~ Ci.5 Z:,J
Cr.idl"n~! r! !'•.! r.~!-: ~~~~! f\C~ 2 0.\ 3.2
~undr:i \'ole 1 (1.1 0.?
!'f·,C"rt.-t . .,' ~ •.:.1 \.'~t.St·l 1 t.l c .. ~
l:lnl: ..1 _.£.:1. _!;(.
T!"J:'}.!, }:J.~"..vJ,:..'t I;] n.e }(:0.0 CG 22.5 }(•,.0 9J 1?.1 \(;C.~
Cnldcr.t!rlcG k1ll• _! ~:!,-
ronL ~:1!..f.'; ~~6 ~,-733
To.Olc'-lO. '. 1,)
.,
J nce:cr:J
!:;ho~~birr!:;
.s:~ort-~arcd
?a;jz~.r!nc:J
::":·"A~ ! r·J ~
(~':::c: 1 ,:vj1 rifj
Du·~kr.
Migratory op~cieo 1 1clcnt1f1c1· froM the
listed 1n yarioun 1~po~tant ~~ciupo I
19(;3·
?cr cent of
of total r.;i;:_:r:1tcry
Nu~tH'"r k111(1~55~ ::3-:l:.'Ci~::;
ij~ 9.7 ~1L9
.,.,
<.) s.o 23.5
Owl:~ a 1.8 8.2
7 1.5 7.1
j~Cf:CI'3) G 1.3 6.1
5 l.l 5.1
Un! •!r:-nt 1 ilcrl
r:,1;:-;:-::to~y ~p~c~.e~ -~ .ld hl
'i'07ili-9fl 21.3 100
t:ur.:t-cr-
16
19
2
21.J
12
, ....
... u
2
~~ '))
),~~ l?70
Fer CC:1~ or ?~'r" CC:lt or
of tot~l ~lr:r-atory or tot.l\1 :::;.sr~t. .. y:·y
!{~ ll (~2~ • 81'f~·~~C!3 Nt:~be::--~ill \7;<) ~~~
5.~ 18.3 99 13.5 49.5
6.5 22 ,ll 37 5.0 1(). 5
0.1 2.~ 2 0.3 1.0
8.2 2S.2 .,.,. 3.7 13.5 ,,
1;,1 14.1 12 1.6 6.0
3.4 11.8 7 1.0 3.;3
0,11 2 .}t 15 2.:! _8_,_g_
28.9 100 2CO 2ll. 3 lCO
1 ~h~;~·n~c ~v1~~ ~p~c1c~ ~nd it in ~~~um~G th.!t rn1grat~~~y ~oec!es e~ a w~ole are the ~ajor ~ou~c~ ~r p~~t1e1ee ~~G
?~~ con~~m!~~t~n~ tr· Grrfnlcon~o
==::::::;:====--
the yearly comparisons made in Tabl~s 7, 8, 9, and 10 are
those gf th~ changes in the frequency of occurrence of
some species in the Gyrfalcon diet over the three-year
period~ To clarify the significance of these chan~es a
brief introduction to some of the changes in prey species
levels ·on the Sev:ard· Peninsula is needed.
It is typical of the far north that both migra-
tory snecies and resident species may vary greatly in
numbers from year to year. As a consequence, the avail-
ability of Gyrfalcon prey species (particularly microtjnes,
rodent-e~ting~birds, and ptarmigan) may change from·year to
year. Gyrfalcons appear to be well adaoted to cope with
this situation, at least in the Alaskan Arctic and sub-
arctic. Cade (1960) notes that on the Colville River in
1959, ptarmigan became scarce by mid-June and l!that the
final gbod fl~dgirg success of these gyrfalcons was made
possible thr-oug-h the fortunate co1ncldence of a sui table
alternate population of large-sized prey ani~als'' (Short-
eared O~ls, Marsh Hawks, Long-tailed Jaegers, and Parasitic
Jaegers attracted to the. resion by ;r.q. moderately high den-·
si ty ·of microtines :r). It appears that a similar situation
occurred on the Seward Peninsula in 1968 and 1970 when
microtin_e ·populations attracted numbers of rodent-eating
birds ta th~ area, particularly the Lon~-tailed Jaeger
which played an important part_in the Gyrfalcons' diet
these tv10 _yc=ars.
65
In 1968, considerable amounts of snow remained
unt.i.l late June on the Seward Peninsula. f-1any migratory
bird species were concentrated along the road system and
in other scattered areas free of snow until early June.
Lemmings, particularly Collared Lemmings, were olentiful.
This species had even appeared in numbers on the snow sur-
face in mid-winter (John Burns, pers. comm., 1971). Hed-
backed Voles were also quite common in grassy 2reas. Con-
sequently, L~ng-tailed Jaegers and Short-eared Owls were
found in large numbers over the tundra. Both Rock Ptarmigan
..
and Will9w PtArmitari~ere-found'in large numbers throughout
the peninsula. Rock, Ptarmi~an Here often located at lm·1
elevations in habitat more characteristic of Willow Ptarmi-
can, and in many instances both species were found nesting
in the same locations~ __ Ground squ~rrels apoeared plent1~ul
and were observed over a wide variety of habitat types.
-lt!aterfm,rl vrcre gcncraJ.ly abunc.1ant ." -Pfntails ~Anas ~lcut__r3_),
in pa:rt:!cular, frequently nested in valley bottoms and
marshei, and occasionally under willows at considerable
distan~e~ fro~ streams. In 1969, light winte~ snowtaiis
and high May temperatures resulted in a rapid snow-melt
which was completed approximately 30 days ahead of the 1368
melt. Relurnins pD_;,~.erines anCl. shorebirds Here observed
scatte.·red~-across the tundra inste2.d of concentrated alone
the cleared road system. During the 1969 summer, microtines
-. -.··-.-· -.
appeared to be virtually non-existent. Only nine Short-
eaPed Owls were observed during the entire summer. Long-
tailed Jaegers were thinly scattered across the peninsula
and the majority of those present were non-breeders ranging
about in small groups and feeding on insects and berries.
Ptarmigan numbers were reduced from the 1968 level and
species segregation was more noticeable. Ground squirrels
were present in large numbers co~parable to the 1968 levels
but also appeared to be more restricted to oarticular
locales. Waterfowl were less coMmon than they had been
·196·8. : }fo du-eks vJerea.iscove'red ne"sting outside-of large
~ "'"' .. LJl
marshes or river syatems. In 1970, generally light snow-
falls and warm May temperatures were again the cause of a
rapid snow-melt. Winter conditions (1969-1970) were such
that a major portion of the peninsula's road system was
open to the public (the 71 mile Nome-Teller road) almost
all winte~. A~ in 1969, snow-melt was completed approximately
30 day~~6ea~ of the 1968 melt. Returning migratory bird
-species, particularly passerines and ~horebirds agajn did
not concent~ate along the road system but were scattered
across the:relatively snow-free tundra. During the 1970
summer considerable microtine activity 1;1as observed. Bodies
of Tundra.Yoles were commonly found in active Rough-legged
Hawk .nests, but Red-backed Voles 2.nd lemminr;s v1ere rare1y
observed_-~· Long-tailed Jaegers were common breeders aJ.tho'1P:;11
they did n¢t_appear to be as numerous as they did in 1968.
67
Short...,earecl Owls Here also comr:10n, but vrere not as numerous
as in 1968. Ptarmigan· mimbers apneared to be slir;htly
hisher than in 1969. However, almost all ptarmigan observed
were Willow Ptarmi~an; very few Rock Ptarmigan were evident
and ntarmle;an species segref~at lon ap;ain occurred. Ground
squirrels were presen~ in large numbers but, as in 1969,
appeared more restricted to particular locales. Waterfowl
numbers did not appear to change from the 1969 level.
'l1 ahle 11 compares by year the occurrence of nine
major ~foups of Gyrfalcon prey snecies in the Seward Penin-
.. esula Gyri'a.±con prey remafns. rrhese prey r;roups include tl1e
three orimary categories of Gyrfalcon prey remains, ptarmi-
gan, ground squirrels, 2nd jaegers and six nd~itional
groupings that include the total numbers of shorebirds,
passerines, microtines, seabird_s-· (Alcids and Larids), cFicks,
and Short-eared Owls. The yearly changes in the occurrence
of ·some--Gyrfalcon l"lrey species on the Set·rard Peninsula are-
shown in Figure 2. The following discussion will certain
primar-ily t~o these data.
~he occurrence of ptarmi~an remains fell sharply
in 1969, and increased to near the 1968 level in 1970 (see
'l'able 11· and Figure 2). 1968 vras a :rhighn ptarmigan year,
and both ·Rock Ptarmigan and Hi1low Ptarmigan were common
along tb~ road system (three to five pairs per mile) and
vrere const;antly flushed while ·hiking ·across· ·c-ount-ry. In
1999, _ fe:n Hock Ptarmigan were observed ar-ter mid-June.
68
1Tab]e 11: Corrlp3.r1sons of thr;-oc:cu:·rence r:i.' J'I~Jl.~'" 'Drey
groups in Se1·rard Pc!1:l.nsula G2n•L'.~C()n nrey
l~e·nJ·, .. l•nc· C0~1fJU·+-·,.,(, u-" ..., .,,.., .. lrly h'J"'~'-.. C-U /, l.1 \__.. .J. ;. .L Ll .) ._.. ( .... Cl•J -L ,_)
____ ! 9 f)=~---__ _] 969 ____ -·-... 1 ~]_():_ _____
Per c!ent Per cent Per cent
Groun -----··-
1l'Ot<?-J:_(!; 56)_ T~t_~~~~L Total ( ·q :() I .•. '
l>t ... r aJ:rnJ_r;a.n 64. ~5 lid. G 59.9
Ground squirrels 9. l.j 21.11 8.7
Jaeger:.; 9.G 5. l.j 13.5
Shorebirds 5.0 6.5 5.0
Pat>scrines , r: -'-•.J 8.2 3.8
-
T!iicrotincs 4.2 1.0 3.8
Seabirds 1·3 lj • 1 1.6
Short -e;,~red ONl s 1.8 0. '1 0.3
65 . -
. 60
55
~ 50 GJ
1-1
>..
11'
1-1
f.\.
~
•.-1 '/15 .
CJ
~ ~
•.l)
J.f "".:""
~I B :>5
~I
0
C)
to.? o•
u
t::
GJ
r.J·
~!
CJ
p.
20 l
I
1
15
10
5
------·---~---:..._ _________________________ ---~·~---····-.. ·····-------
ptarmigan
jacgers
gioun~ squirrels
..shorebirds.
n;i•::ro tines
1968 1969 1970
Y e a r
Figure 2. Pcrce~t~ge occurrenc~ of selected groups
of prey spc.:i.cs .i~~ ,;u!~n,er Gyrfalcon pl"t!.y rcinair.s fro:n
t:t·H~ Se\o.'ard T~t:!!il:!:.ul~·i, .-\las.J-~a, 19h~1-1970. Prey grcups
that incraas2d during 1969 are represented by dashed
li!1~~s ..
70
Willow Ptarmigan observations averaged about one pair per
·thr~e to fi~~ ~il~s of road in some of the optimal Willow
Ptarmigan habitat. In 1970, Rock Ptarmigan, never observed
to be numerous that summer, were not seen after about the
.
first week of June with the exception of three specimens
collected in August. Willow Ptarmigan were commonly observed
all summer but remained below the observed 1968 level.
Family groups and small flocks of this species became common
in mid-July and _August. Local hunters comr.1ented that otar-
mig~n se~med ·scarce in 1969, hut that in 1970 hunting was
. better and-t11at-th.ere were again !r lots of birds. ;r These
observations suggest that the entire nt~rmigan population
declined in 1969 but rose again in 1970 due primarily to
an increase in Willow Ptarmigan. However, the 1970 level.
did not attain that of the. 1968 high. Figure 3 s11ows
that the f~equency of ptarmigan in the Gyrfalcon prey
remaJns agrees vli th my subjective observations of the ptar-
mi"gan population.
The occurrence of jaegers in the Gyrfalcon prey
remains fell in 1969, but increased in 1970 to a level
above_that found in 1968 (see Table 11 and Figure 2). Nine-
teen sixty-eight was a high jaege~ year: All three species
t._rere common breeders' especially in the southern half of
the peninsula. Long-tailed Jaegers were by far the most
abUrtdantf Pomarine Jaegers were the least abundant. Long-
tailed Jaeg.ers Nere commonly observed catching and eating
65
60
55 .
50
45 .
0
""L--
'l.
A------~
o-----<>
Ptarruican p0pulaiion esti~ate
Oc~urrencc of ptarmigan in
prey remainG
I _j
L ______ _L ____ ~_j _________ j _________ .......J
1963 1969 1970
Y C! a r
Figure 3. Th~ percentage occurrrnce of pt&rmisan
in ~:'!lc 196( -1970 Gyrfalc>on pr.~y r0mains co;;!p;;red
\ilth an cbscn·ed st<Ljcctive est5~:;tc o£ ptc;rini_;:;an ·
poptllction Lrend:.; from the Scuard Peninsula, Alaska.
100
75
50
O) r:..;:;
('j C\
rl r:
0 ~
r.~
'"d (l
~ ~
!I)
~ ~ -':l ••• ,,
<:.> r, lJ
t1l c
C) t;-o~
!I)
r; --~
t' "'> .;:t h; ., .....
('j
r--i t~
:.:! C:J c ... C...l
0..-l
A.
()
:> >.
•rl '~
.,LJ ~
C.' H
Ci .1.J
25 :r.,• :11 ::; };
Vl;,;
I)
·-1 / ..
72
Collared Lem~ings, B~ciwn Lemmings, and voles. Counts as
hir;h as-100 birds were common on one 35-r:lile stretch of
the Teller Road.
In 1969, only one observation of a small group
of Pomarine Jae[:::c:r·s \'!2S r'lade, anrl that occuT'Y'r:.: ;;'X!'ing
spring migration. A few Parasitic Jaegers were observed
along the ~outhern coast and a few pairs of this species
apparently bred near Safety La~oon. Long-tailed Jaegers
were thinly scattered across the peninsula. A few nestinG
pairs of this species were found but the majority of those
observed .did not appea~ to breed and were in small groups
of 10 to ~0 that wer~ Nandering aeross the tundra eating
insects and berries. In 19'10, Po::1arine Jaee;ers, though
present,_were scarce. Parasitic Jaegers were again present,
though not in the numbers observed in 1968. Long-tailed
Jaegers were agai~ common although somewhat below their
1968 level. Long-tailed Jaegers were observed catching and
eatir1g vol~-$ ( almos_t _certainly Tundra Voles). Observations
th~refore suggest that the jaeger populations, and in
particular Long-tailed Jaegers, declined in 1~69 and ro~~
again ~n 1970 probably due to an increase in Tundra Vole
numbers, -to a level approachine; but belm'l the 1968 high.
In Figure-ll the frequency plot of 5 aeger 2 . remains also -. ·-.
· 2 The t.Qt_,.'ll-j aer?;er remains are almost ent.trely Long-tailed
-Jaegers. It is interesting to note that for unknown rea-
sons·this species took the brunt of Gyrfalcon predatJon,
while th~ other two jaeger species were almost entirely
untouchE?\1·
0 eo
('j
30
~ 15
Gl u
~~
Q)
p.. l.
JO L
'~
I
--------------------------
-4t
\
\
\
\
\
\
\
Ct-----1;. Jaeger population estimate
c-----o Occ.urrence of jaeeers .in
prey rern~i.ns.
\ .¢.
\ ,
\ ,
\ I
\ /
\ /
' I \ I
\ /
\ /
-~ ·/ .
\ I
\ I
\ // /
0'--.. \VI -~ 'd
~~ j
I
o L_. ____ _: ___ l ______ j __ _ __ _j _____________ _j
19GB 1969 1970
Y e a r
Figure 4. The perccuLage occurrence of Jaegers
in the 1968 -1970 Gyrfalcon prey .~s~ains co~parcd
with an observed subjective estirn3tC of j&eger
-·papulc:llorl tre:1ds !ro~u the Se~ .. "ard I·c-~ninsula, Al3.sk;,
lCO
.
(.C
-.D
C'.
.;
t:! H
0 <!
Col
"\1 :--.
!lJ
~~ l!} r.: .~~
.D .u
75 ~ ~
0
c,:) t:~
u
ul -~
Q)
r.: > 0 <!)
-rl r-1
<J
74
appears to follow the trend of my subjective observation
--of the jaeger population.
The percentage of microtine kills in the Gyr-
falcon prey remains fell in 1969 and rose again in 1970 to
a level comparable to that of 1968 (see Table 11 and Fig11res
2 and 5). The 1968 season was a year of abundance for
microtine species in general, particularly Collared Lemmings
and Red-backed Voles; Brown Lemmings and Tundra Voles were
also cor.1mon. _In marry areas Collared Lemminss were found on
the tundra in quantities that allowed a collector to cap-
ture numbers of them by hand. Prior to the 1968 summer a
build-up in microtine numbers had apparently occurred.
Microtine trapping data from John Burns (oers. comm., 1971)
indicate that. in the vicinity of Nome trapning success
increased T~om about 11 per cent in July 1967 (1~3 trap-
nights) _to about e. 0 per cent in October ( iW9. trap-nights) .
Duri~g mid~October one area produced 41 animals in 144 trap-
nigh~s--a success of about 28 per cent. Following this
general build-up, primarily of Collared Lemmings and Red-
backed V6les, Collared Lemmings were observed moving about
on top of the snow durin~ the winter 1967-1968--an appar-
en_tly un_usual o"ccurrence (John Burns, pers. comm., 1971).
puring the summer of 1968 Burns reported a trapping suc6ess
-..
of about 40 oer cent in early summer with an increase to
. . .
high as··Gs per cent by late Aucus t. These trapping data
indicate that of the four species discussed, Collared
-~.,·----··-· ... _______ -------------~--·--·--·-"'1
30 ~ ~
\
\
. ··•!' J.I}C"I 4-·----~.:~ !--r.~~c"('::_;jr~~ pnp·.i.l~~-ti0n
(>,, ll ... ,.t...,
C!------·------o <?cc.urrt:1r:~ cf :Pit,::0tint.~S
~ .. ... .: c:::
...-::
hC'
C.-i
1!1 25
{)
r.
Q)
1-< r ~~
:: 20 -~
N1
·~ ..,
r::
~
(..'
I<
()
1'4
15 -·
5
\
'
10 prey remaJns ~l)
\
\
\
\
\
\
\ I
\ I ,. I
\ /L l
\ ! 1 \ /; I
\ I ~
\ I I
\/ __..-o j
-c..___-....__________ '>r. _________ __..___...... I
" -I -,.,)____ I
v l---..----.. --------J-... ~------·-·--··-·--...... 1 ..... --~--·--·-.. --_ _L_ ....... _ .... ___ , ____ ~I
1%8 l%9 1970
'l a r
Figure 5-TLil~ pereen t.::tVJE ,~o~:c~· rr2nc!!. (. ~
microrin(S i~ tl1e 196S--l97C-Gyrfalcon
prey remains co;~rpared vit~; ?;1 0b;;erved
ftubjcct:ive l?stin:Htc cf r;}_c·t·otl.:·:e ~-"-""ru1...:•.-
tion trend~-: frc·m th;..: Se!,.JGr1 Fenii!sula 1
Alaska.
(j) f-t'.1J . .:t ::i!lci.Lys J :; :i: <0 i Ciltf:'J
microtinc~ occ~!!. ~Lc~i~ f!~2
t1mr.~; ;J.::-.. :.:~tt~'r:. ;~~ ;:~·~·-prL~y 1·t:··~
P.l[~lft~~ p~.O ~ t etJ CF t h5. ~: gr~. t·h l ..
.. ,:: ~.
;jJ '"· (/! ;:l
c;: ~'
,.C;
75 c -~ -·-l .u
r.1 ). ...
~~ v
<;;
~
Q -:
~-1 G.· ._J :,
C) (:}
50~~ d
:..~. ~.t
~~ .~:
•• J
d.: > :.,-..,
·~·i ~-·
~J ~;
0 ~
'.J "-:
T) ••i
25 .!""I·~
~'J ~
Lemmi-ngs were the dominant species c:md the rrundra Vole 'il3.S
the least abundant. In 1969, all microtine species appeared
sc~~c~; however, a few Tundra Voles were observed crossing . .
roads and small numbers of this species were present in some
areas, at least on the southern half of the nen:Lnsu1a.
Three hundred fifty trap-nights in three good 1968 ~icro-
tine habitats near the active Gyrf:.l1con eyrie::> nrodnced
only one Red-backed Vole. Burns (pers. comm., 1971) re-
ported a catch -o·f only· 25 anim::J_l-s ·of the· ass6rted species
in 1 3 070 trap-nights in July 1969. During 1970, a few
Collared LeE1mings and Red-backed Voles were observed
lng roads ann were r·arely encountered on the tunclro..
Tund:ea Voles Her~. freauently o_b~erved. _ .!~ouc;h-legro:ed
j ae;~;ers ,. and .Short-e;:~u'"'ed ·O~·Jls \·Jere observed cat chine and
e2.ting; them~ they \·Jere commonly f"ound. in Rour,h-legsec~ 1 l'1\·ri<
nests~ The percentage of nicrotine kills found in the prey
remains generally followed the estimate of the th~e~-y~ar
trend in the microtine populations (see Figure 5).
-The general high pooulation of microtines in 1968
attracted a large number of rodent-eating birds~ including,
besides the jaegers, a few Marsh Hawks and·many Short-eared
Owls. In 1968 up to 12 Short-eared Owls were commonly db-
served along many one-mile sections of road. By P!Tay 1969,
the micro-tines had undergone a c;eneral population "crash!!
and were-scarce. This condition drastically reduced the
numbers of·rodent-entin~ birds on the Seward Peninsula th:::tt
77
season. Only nine Short~eared Owls were observed during
the entir~-1969 summer and eight of these birds were in two
family groups observed hunting along the Kuzitrin River
during mid-August. In 1970, an increase in the numbers of
the mi~rotine~, prima~ily the Tundra Vole, again attracted
·. large_ .numbers of rodent-eating birds to-the Sev:a~d Penin-
sul~ (again including a few Marsh Hawks), alth~ugh below
the numbe~s observed in 1968. Short-eared Owls were again
common. ~aunts alo0g a 3Q-mile ~tretch of road in tha-
-'-Kou·garot-:-:Kuzitrln.:.1>iTg-rim--R.iver systems ranged from 25-30
individuals throughout the summer--an average of about one
·Sho~t~~ared Owl per mile. The percentage of Short-eared
/"--""'\ _ ONJ.-s in the prey re1rtains fell in 1969 and continued to fall
_\·--:-_! __ in_~_l9TO ir1 spite gf an -observed-increase ·in number in-
-----·-
197:0-(s·ee T9,bTe.c.lO and 'Figure 2}. 'i1he significance of this
case, inconsistent Ni th the general picture~ ·cannot be
··-
asses·sed.
The foregoing outlines a situation in which 1969
-·--population deciines in three groups of prey species, ptar-
migah, rodent-eating birds; and microtines, were correlate_d
-·-
with a l.ov..rer percentage of these _species in coll~cted Gyr,....
falconJir.~Y: ___ re_m_a;i._ns _. The remaining Gyr-falcon prey groups -
ducks_ (s~e~-~'J':iible 11 and Figure 2) rose in proportionate-·.------.;: .. :·. ----~ . ' --. -.
representa.t'ion in Gyrfalcon food iri 1969.
·:"' Tfie crccurrence of ground squirrels in Gyrfalcon
--.,... __ •...!,.. •• ~ .. ..-;;. •• -:·.-·-1
·-------
. ___ ._,.
~ ~ . -------.-·.:~-;.: .. :-~::.-: ..
..
food remains, while rising in 1969, declined to slightly
be~ow~he 1968 level in 1970 (see Table 11 and Figure 2).
Gro~nd ~quirrels were abundant oyer most of the Se~a~d
Peninsula du~5ng all three years and were commonly observed'
the entire lerigth of the road system and on every over:....land
hike.~ Actual numbers ot ground squirrels did not really
appear-changed fro~ those found in 1968 and certainly any
change that may have occurred was relatively small and not
easily detected. Figure 6 shows the sharp increase in the
· .. · .. ·----__ ; ___ --~-----·· ·.·:.-
per qqnt of ground squirrels in the Gyrfalcon prey remains
in 1969_, vlhi1e the ~stimated ground squirrel population
indicates little change over the three-year period.
The remaining prey specles, consisting_
-o:f. passer·:tne::r;-shorebirds, ducks, and se-abirds, a!'l show
the-same tlpward tendency ·in their occurrence in the 1969
Gyrfalcon prey remains. These groups did not appear to
exhibit any-note-worthy changes in_population numbers over
. -___ ---.-.. --·· -·-·
the ye_-~:rs ..
Tbese data indicate that the 1969 declines in
numbers a~d availability of some Gyrfalcon prey species,
primariX_y: .. ptarmigan and Long-ta.iled Jaegers, on the Sevmrd
Peninsu1-a-resulted in t·hes-e species being taken .to-a les·ser
. ,__; -.. · ..
deg.ree hy Gyrfalcons, and that other species, specifically
.the, Arct_:L¢=·c~Ground -Squirre-l-,--were taken ·to a-hi.gher-·degree
as a meq.g_s_ of compensation. Because ground squirrels are
tc3 an .impot~aQ~ Gyrfalcon prey species on the Se\1ard Peninsula,
'79
both by number and by weight, and were relatively plentiful,
these data suggest that Gyrfalcons relied heavily on this
species in 1969 to compensate for the lack of other prey
Bpecies. $ince ground squirrel numbers did not appear to
~change to any important extent over the three-year period,
I believe that the increase in the occurrence of thi~ spe~
cies in the Gyrfalcon prey remains indicates a higher degree
of utilization, not because ground squirrels were more
abund~nt but because other prey species were less abundant.
VJh-ether 'ground 'squlr-;rels-~rere -·hurited-"sele-ctively,· or wh~ther
-
they were simply killed more frequently because they were
-· . ~-. -
there and available is unknown. In either case, how·ever, it
app-ear3 that the increase in utilization of the Arctic Ground·
Squj_t>-rel vva-s an--important form· of compensation in 1969:, wh-en
ptarmigan,· Jaegers·, and microtines declined. It appears
that, like ground squirrels, the passerines, shorebirds,
ducks-, ·all:d seabirds played-a rol--e-in-the 1969 Gyrfalcon··
.. · , ..
diet as_ c __ ?mpensation for the dec1ine of the other prey popu-
lation, though to a much Jesser extent. Though important
prey compensation apparently took place in 1969, there was
an aprr~9Ximate 25 per cent decline of the Gyrfalcon popula-
tion Nit l-it.!} the sub-:-s tudy area and ·its .. su_b-uni t, Area I,
·that year.:·{see·page 20). It is possible that the prey
became available too ~at~ in the Gyrfaldon breeding cycle
to prevent some pairs from abandoning the area. Ground
o.
~~· "-J·
Ql 25
0
~
C!) ,..,
B u
0
5
A--....... .:...:_ . . . •
----~-t:X-~ ..... ---------.6. 100
• 75
A-----t. Ground squirrel population estimate 25
0._..._,_~-o OccurrE!nce of ground squirrels
in prey re;aains.
1
.
J~=---· __ .~_r ____ ...;._ _ _:._.;.-.:..~..;__ _____ .l..r _____ --J 0 1968 1969 1970
y·· e a r
Figure 6. The percentage occurrence of
Arctic Ground Squirrels }.n the 1968:-.1970
Gyffalcon ·prey remains co~pared >Ji.th an
observed subjective estimate of the ground
squi-rreJ:-population trends from the Seward
·Peo,insuia,· Alaska.
.
t::(O
rJ \,Q.
C\ ......
-~ ...
0
i.
•.
.·~ \-.Y
80
_squirvels are unavailable io Gyrfalcons from about 1 October
to l May ·.due :to their vlinter hibernation.-
Tp eJnphas.iz_e the apparent importance of ground
.squirrels to Gyrfalcons nesting on the Seward Peninsula in
1969, a plot of the calculated per cent by weight of the
yearly ~urns of avian species and mammalian species ideriti~
.fied Erom the prey remains has been made (see Figure 7).
This figur~ indicates that, by weight, avian species
declined ~bout 13 per cent in 1969, while in this same year
ground. squirrels; by ~Ieight, increased about 13 per cent ln
·the Gyrfalcon pr~y remains. Table 6 (fr~m which the plot
vras obtained) sho'trs that during all three years ground
squirrels, by weight, constituted almost all of the mammalian
.... ·· contr.J.bution -to the prey remains. Simj_larly, the approxi-
mately 13 per cent decrease in the 1969 avian kill can be
...
attributed to a J.arge extent to the decline, by weight, of
ptarmigan and jaeger~.
Figure 8 is an attempt to show the compen~atory
role. played by ground sql,l.ir_rels and the rel.~.tionships of
the three .. important categories· (ptarmigan, j aegers, ·and
ground squirrels). PtarMigan and_jaegers, together by
~~ight, rleclined sharply in 1969 (Curve C). On the other
hanq,-"f>he-;three primary categories including ground
. sc:quirrels::~curve A),-· together by Neight, . did not decline as
sharpl~ ~n~969. Grouping ptarmigan and ground squirrel~
\~~----(Cur-v-~-.:-:BJ:~~: thes.e tvw categories by Neight. res.ulted in the.
--:~---~--~ -. ·.--.
95.
90
85
80·
"-' ..c: eo
•.-I
~
~
>. .a
~ eo
<11
.j..l· 25 ~
~
C)
H
-~
ll:<
20
~~
\ _ _) 15
10
5
~ \J_·
,.-..------------------~-----------·---·-·--~-----------,
(A)
(B)
1968 1969 1970
Y e a r
·rigure 7. (A) The estimated biomass of ptarmigan and
... Long-tailed Jaegers calculated as a p~t;c::entage hy
· · ·l~teight of" the avian rem.:lins, and. (B) the estimated
. · biomass or· Arctic Ground. Squirrels calculated -a£ .a
· ~.percentage. bY tveight of the rr.aa~~lian· remains identi..:..
, :,fled .from the .1968 -1970 Seward Peninsula Gyrfalcon
-:;~·:PI"~ remains.
100
95
90 .
. 85
80
75
u ~ 70
.... •rl
Q)
.:?.
65 .>. .
,0
20
15
io
·s
·o-
(A)'-.._.
'--__ ___L_ ______ _J..i ------''_;__----1
1968 196_9 1970 .
y e a r
Figure 8. Major Gyrfalcon pr~y item~-e~pressed as a percent-
--_ ag~-of the tot.:;.l of yearly kills by· weigtt: {A) ptarniigan,
j ;~-~g-ers, ground squirrels; (B) ptarmigai1, ground squirrels';
(cf'ptarmigan, jaegers; (D) ground squirrels, jaegers •
. : -~----·:__,_ __ . --
--.: ____ _
._:_·~-)~--. ..
~
83
flattest curve. This indicates a nore stable yearly utili-
zation of these two resident species in changing combina-
tions. However, grouping ground squirrels and jaegers
(Curve D) shows that these two categories together by
w~ight, increa&ed in 1969, even though jaegers contributed
the lea~t amoun~ by weight and, in fact, declined irt numbe~
of occurrences-that year. The increased occurrence of
ground squirrels indicates them to be an jmportant source
of food that helped "buffera the decrines in ptarmigan and
jaeg~r biomass.
it ~ust be reiterated that based on p~llet exam~
ination,· it was estimated that microtines occurred up to
5 times more frequently than was evident from the prey
·remains~· rn·terms of calculated biomass and percentage by
weighti-this fact-has very little effect on the calculated
Values presented on the basis of the prey remains alone
(one per· cent--or less)~-In._fact, i'lere -microtines to occur
up to fen--times the number they represent in terms of prey
remains, -the results· in t_er-~s of percentage by \'Ieight. cal-
culations are still affected only to a minor degree;
Because of the differences in the ye-arly sample
_ .sizes o~ _the Gyrfalcon prey remains, a _2 X 2 contingency
table ~as~constructed and chi-iquare values were obtained
-
to he:J..p-0:0.lnpare by year the prey groups _listed in Table 11.
In all cg,_ses, \'lith the exception of the Short-eared 01-..rls,
(-"' the chi-~-qlJ.Stre value followed a pattern that is consistent
'~ --·"-'""·
-. . &J ". ',· ... '! ..
,.
(_-_) vii th the picture presented by Figure 2 and the hypothesis
that utilization of some prey groups increased in 1969 when
other prey groups became less available to Gyrfalcons.
Variatfon in prey species utilization betv1een different
pairs
Tables 12a~b to 27a~b list prey remains fr6m a
series of Seward Peninsula Gyrfalcon eyri~s where 25 or
more. kills v1ere found .. 'l'hese tables describe a range of
variability of prey vlithin ·a s·ample of 23 Gy!'falcon nestings
in differ-ing hal?itats and situations. T1,v0 factors may
account-·· for this variation: ·( l) the location of the eyries
in relation to prey species habitat and numbers, and (2)
.~
pair or individual preferences on the part of the Gyrfalcons.
To· demonstrate the variation in prey remains that occurred
betw~~ri the Gyrfalcon eyries described in Tables 12a,b
through 27aib, the three major prey categories (ptarmigan,
j aege:rs_, ~nd ground·. squirrels), migratory bird species and
resident species were ex:tracte.d. and are presented. in Table
28. It·· may p.1s:o .be _noted that of the 23 nestings ·listed
where prey remains were col-lected, ptarmigan occur in every
iristanc~, ground squirrels occur in 21, and jaegers occur
. "·-'---"• ·Tn: l4>:·::o:he or ·more of the. resident species. occurred in all
the nes.~iYrgs and migratory bird species occurred in 22.
·:.:"':It has been previously mentioned that Gyrfalcons·
_::-_:~_-:_....__:. __ ,
·ne~rting "in insular situations feed primarily on Alclds,
--_-.. ···' .. _,_
..
~-~
\--1
. "..___/
;~ -~
.'-:~-,-=~
85
Tabl~ 12a. Gyrfalcon ~yrie no. 1 1 , Seward Peninsula,
Alaska
1968 1970
Per cent Per cent
Name Number of kill Number of kill ---
Long-tailed Jaeger 15 29.4 81 55.9
Ptarmig·an species 18 35.3 214 16.6
Bl~ck-legged ~ittiwake 3 5.9 11 7.6
Unidet1tified birds 3 5.9 5 3.4
American Golden Plover 1 2.0 3 2.1
v1himbre1. · 1 2.0 3 2.1
Pintail 2 3.9 1" 0.7
Unidentif-ied waterfowl 3 2.1
U:nident_ified shorebirds 3 2.1
Bar~ tailed Godt.fit_· 1 .2.0. 2 1.4
Unidentified Alcids 3 5.9
·Black ·sra:nt ·· · 1 0.7
Green~winged Teal 1 2.-0
Ruddy_ T1:1:rnstone 1 0.7
Parasitic Jaeger 1 0.7
Short~eare_<i .Owl 1 2.0
LapHlrid Longspu·r 1 2.0
Unidentified passerines 1 ~ ..
TOTAL BIRDS 50 98 .J 140 95.7
Arctic Ground _Squ:!-rrels .. 1 2.0 ll 2 . .s
Vole sp~·gies 1 -0. 7.
TOTAL MAMf>'IALS 1 2.0 5 3.5
TOTAL KILLS 51 145
1 Eyrie. no·:· 1. is located overlooking the sea above a narroH
coastal: plain.
-_:..:· __ . __ ..,_ ---· ~-·-···
................. ____ ..__... __ .. ____ ........ ...-~
·-86
.-'rab·le 12b. ·Gyrfalcon foo·d ·remains from Table 12a. grouped
in various major food categories
C~ategory
Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Short..:..eared Owl
unidentified birds
Migratory-b-irds ·
subtotal··
Ptarmigan. ..· .. Grouncf -s-quirrels
l\Ucrotines ··
. . .
Resident species
-,sub't;ot;§:l __ _
-~ta~migan~ jaegers,
an:dground squirrels
P~armigan and j aef;ers
--------
Pt_armigan and ground
squirr~J§
lF· __ l_gu:ses -_f:or -1968 are
2F· _ 1:-gures . for 1970 are
·······-
--: ~-. .::..:..::
--=-----. -· -0.. .--''....0::..:..
1968 1 19702
Per cent Per cent
Number of kill Number Of kill
3
3
1
15
6
1
_l
32
18
1
19
33
19
..
calculated
5.9
5.9
2.0
29.4
11.7
2.0
. 5. 9
61.5
34.6
1.9
--
36.5
65 .1~
63.5
36.5
on the
calculated-on-the
5 3 . lt
12 8.3
1 0.7
82 56.5
11 7.6
_2 ~
116 80.0
211 16.6
4 2.8
1 ~
..
29 20.0
109 75.2
105 72-.4
28 19.3
basis of 51 ld.lls.
basi-s ·of 145-kill~ •
1 Table l3a; Qyrfalcon eyrie rio~ 2 1 , S~ward Peninsula, Alaska
' ij
j'·· .N· :. :.:. :\: ·/.: • 'j_;
·= arnet .:\. -i\ •· -~··!;;:·!,
P~anmi~an s~ecies '
Long-tailed ,jaegers ;
Jae~er species • · ,
Unidentified shorebirds
Americ~n Golden Pl6ver
1t!himbre 1 ·'
. Par~keet: Auklet ··
Unidentified passerjnes
Unidentified birds
' TOTAL ·BIRDS
Ar,ct.ic Ground Squirrel
Brbwh ·Lemming ' . -
po:I1ared Lemming
I •• '
TOTAL MAMMALS
' . TOTAL KILLS
,•j ' ' ·~
••• ••• r J \, :
Number
;2lf
'2(
1
+
53
1.
1
2
55
I ' : ..
1:968
P~r:cent
of kill
L13. 6
4q,l
i.B
1.8
96.4
1.8
1.8
3~6
.....
Number
fe,r .rent·
iQf kill
37 ·74.0'
6 J-2.0
I
1 2.0
1 2.0
1~8 96.0
2 1!. 0
2 l!. 0
,50
I
Number.
74
4
1
1
1
1
82
1
1
2
84
Per cent·
of kill
;.
·88.1
4,. 8
1.2
1.2
1.2
1.2
97.7
1.2
1.2
2 ,l!
'iT? '• 2 .. .Gyrle no.. . ls located at an inland river bluff in a narrow valley, 10 ~ir-miles from
the coast.
2This'eyrie was
·probably r"970.
I. I . :
---r
.• ) I
occupied py the same pair of g~rf~lcon~ during 1968 and 1969, and
. !
i .
~ . •
! •
! '
' '
! I:
I·'
!
Cl].' ... · ...
L I
~ ! .
Table l3b. G~rfalc6n fobd remain~ from Tabl~ 13a g~ouped in various major categories
.••,,
• : .. i, ·:, ' . . ' i . i ' ~
:) .. l >i ·JI,: : ii \. .: ! :1 ~.~.· ' ,. ., )
. Ga't'e·gotv · '\i .I :·! ·; .;-_. '.'_v,.: ..•.
' ::; ;
·nucks:' ·
$hqr~birds
Passerines
Jaeg~rs:
·seabirds
.Unidentified birds
i·
19681 __ .._
'I i ' ' · Per cent Nti~b~r· of kill
··r i 1·. 8
j8
!
50.9
-:--·--
Migrato~y birds subtotal 29 52.7
Ptarmigan
Grdurid squi~rels
:.1ic:rotines
24
1
1
Reiident ~pecies subtotal . 26
; j
!
Ptarmigan~ jaegers, a~d
grou~d .sqtifrrels
~tarmigan a~d j~egers
Ptarmigan and :ground
· . squirrels
!Figures for 1968 are
?Figures for 1969 are
3Figures for 1970 are
53
52
25
caJ!culated
calculated
calculated
43.6
1.8
1 .. 8
47.3
96.4
94.5
l{ 5 . li
on the basis
on the basis
on the bas:i.s
of 55 kills.
of 50 kills.
of 81.t. kills.
·--.-.....
'~
'~ _ _)
Table i4a.
.. . ... ·1.
Gyrfalcon eyrie no. 3 , Seward Peninsula,
[\_laska ·
1968 1969 2
89
Per cent Per cent
Name Number· of kill Number of kill -
Ptarmigan species 10 32.3 16 38.1
Robins 3 7.1
Unidentified passerines 3 9.7 2 4.8
Bar-tailed Godwits 2 6.5
American Golden Plover 2 4.8
Long-tailed Jaegers 2 1L8
-RedpoJ.ls. 2 4.8
Jaeger species 1 3.2
Whimbrel 1 2.4
Ruddy Turnstone 1 2. lj
.. Tr-ee Sparrow. __ 1 . 2. 4
GraY:-che-eked Thrush 1 2. 1+
Unidentified shorebird-1 2 ~ Ll
Unidentified bird .: 1 2.4
-TOTAL BIRDS 16 51.7 33 61L 5
Ground squirrels 15 48.4 _2_ 21.4
TOTAL M.f\.l'lfr1f!.LS 15.: 48.4 9 2l.l.J
---ToTAL KILLS 31 42
· 1 Eyrle .110 ~-3 is located on the lm'ler slopes of a narrow ·
river va·lley 8 air-miles from the coast.
2This ··eyrie "~>Tas occupied by the same pair of Gyrfalcons
-1968-:19.69.
, ... .,....· .
.. ,·.,_:-.; ._·.
-
I
j
I
l
I
i
.!
I
90
Tab~e l4b. Gyrfalcon food remain~ from Table l4a g~buped
in various major categories
Per cent Per cent
Category
Ducks
Shor-ebirds
Passerines
Number of kill Number of kill
_Jaegers
Seabird
Unidentified birds
fliigratOJ?Y -bir_cts sub~otal
Ptarmigan __
Ground squirrels
Nicrotines
Resident species subtotal
Ptarmigan, jaegers, and
_ ground squirrels
Ptarmigari and jaegers
Ptarmigan and ground
squirrels
2
3
1
6
10
15
25
26
11
?I')
'-./
1 Figures for.l968 are calculated
2--. __ -_ -----Figures-:for--1969 are -calculated
,..~,-·,L.,::-._· ...
6.5
9-7
3.2
19.4
32.3
}~ 8 . lj
-so. 7
83.9
35.5
80.7
on the
on the
5
9
2
1
17
16
9
-25
25
basis of
---
basis of
11.9
21.4--
4.8
2 .1-J
4-o .-s
23.8
21.1~
59~5
-59.5
31 kills.
42 kills.
() Tabie t5a. Gyrfalcon eyrie no. 41 , Sevmrd J;eninsula,
/\ \ J
'·._/
Alaska·
Name ----
Ptarmigan species
Tufted Puffins
Pigeon Guillemots
Unidentified v.raterfowl
Unidentified passerines
Unidentified birds
h'himbrel
Unidentified shorebirds
Long-tailed .Jaeg·er's-
_Robins
TOT AT_, BIRDS
Ground squirrels
1
.-
-TOTAL r1Ar.'IMALS
TO'rAt. KILLS
Eyrie no.-4 is located
a seabird-
---. ~-~
,--.:--·-
colony.
··· .,.
-. . . <.~
1969
?er cent
Number of kill
ll 26.8
7 17.1
4 9.8
3 7.3
2 1L9
2 4.9
l 2 • 1~
1 2,11
l 2.4
l 2.4
33 80.4
8 . 19.5
8 19.5
1!1
on a, sea-cliff on the periphery of
92
Table 15b. Gyrfalcon food remains from Table 15a grouped
in_ various-major categories
Categor~
Du-cks
Shorebirds
Passerines
Jaegers
Seabirds
Unidentified birds
Migra~ory birds subtotal
Ptarmigan
f.1icrotines
Resident speci~s subtotal
Ptarmj_p;an ,-.) aeg-ers, and --
Ptar~igan and jaegers
Ptarmigan and grJund
squirrels
Number
3
2
3
1
11
2
22
ll
0
C)
19
20
12
19
19691
Per cent
of kill
7.3
4. 9-
7.3
2.4
26.8
~.__2.
53.7
26.8
19.5
46.3
I.,-,
Lj o . ·r
29.3
46.3
1 Figures for 1969 are calculated on the basis of 41 kills.
'('
.~\
Table 16a. Gyrfalcon eyrie no~ 5 1 , sekard Peninstila, Alaska
i
'Ji:'" . I
Name
Ptarmigan specie~
Common snipe ,
American Golden Plover
Jaeger species
Short-eared Ovll
Robin
Unidentified passerines
'l10TAL BIRDS
Arctic Ground Squirrels·
Collared Lemmin~
Brown Lemming
Vole species
· TOTAL MAMr·1ALS
:,l,OT AL KILLS ·
Number·
.8
5
2
1
1
17
8.
8
}~
1.
21
38
1968 ' "
Per cent'
of kill
21.1
13.2
5.3
2.6
2.6
:4 4. 8
21.1
21.1
10.5
2.6
55.3
.. 1969'
Number
· Per cent or kill
8
1
"!
1
10
1
1
11
72.7
' 9.1
' 9.1
90.9
g,l
9.1
1970
Per cent
Number of.kill
29 67.4
1 2. 3
3 7. 0
1 2. 3
1 ~
35 81.3
'
5 11.6
2 ' 1+ • 7
1 2.3
8 18.6
)~ 3
1 Eyri~ no. 5 is lo6ated on a hillside in a narrow valley system 23 air-miles:from
the coast.
'1 .,
. I
\ !
{0 r;, ')
111'
[),, I
{~ ~I )
'---·······
Table 16b. Gyrfalcon food remains from Table· l6i grouped in var~ous major categories
.1968 1
I ' '
:;·. ,i l'::i i>Cate€;or.lf:'
·,
I ·., Ducks
. Shorebirds·
Passerines
,Jaegers
Seabirds
Short-eare<;i 0111
Number
7
1'
Migratory birds subtotal
1
9
8
8
Ptarmigan
Ground squirrels
Microtines .u_
Resi~ent species subtdtal· 29
' Ptarmigan, jaeg~~s,, and
ground ~quirr~ls
Ptarmigan and Jaegers
Ptarmigan and ground
squirrels 16
' i ~Figures for 1968 are calculated
Figures.for 1969 are calculated
3Figures.for 1970 are calculated
Per cent
'f' 0~ kill Number
42.1 9
on the basis of 38
on the basis of 11
on the basis .of 43
19692 ·
.,
:P'er cent
•' .·
i ;
of kill
: 9.1
': 9.1
. 18.9
72.7
9.1
81.8
I
81.8
kills•
kills:.
kills.
:Number
4
1
1
6
29
5
_l
37
.35'
30
3L1
19703
I
Pe.r cent
df kili
14.0
67.4
11.6
~
86.0
81. 3~
69.7
79.0
95
Table 17a~ Gyrfalcon eyrie ~o. 61 , Seward Peninsula,
Alaska
Name
Ptarmigan species
American Golden Plover
Robin
Gray~cheeked Thrush
Long-tailed Jaeger
Semipalmated Plover
Unidentified shorebirds
Lapland Longspur
Unidentified p~sser~nes
. TO'J:IAL BIRDS
Ground squirrels
Collared Lern-ming
TOTAL rJIAMr·iALS 7
TOTAL KILLS
Number
8
6
3
2
1
1
1
1
1
24
38
1
39
63
1969
Per cent
of kill
12.7
9.5
4.8
3.2
1.6
1.6
1.6
1.6
1·. 6
38.2
60.3
1.6
61.9
1 Eyri~ no.-6 is located on a hilltop in a wide river valley
11 air-miles from the coast.
-
---- - - -
Table ~7b. Gyrfalcon food remains from Table 17a grouped
in various major categories
Category
Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Migratory bird5 subtotal
Ptarmigan
Ground squirrels
Microtines
Resident species subtotal
Ptarmigan; jaegers, and
ground squirrels
Ptarmigan and jaegers
Ptarmigan and ground
squlrrels
Nurr:ber
8
7
1
16
8
-:<R
..J"
1
Jn
117
9
116
1969 1
Per cent
of kill
12.7
11.1
1.6
25.4
12.7
C:.r. ..., uv • .) , c:.
...1... • 1._}
74.6
71!. 6
11~. 3
73.0
1 Figures for 1969 are calculated on the basis of 63 kills.
97
Table 18a~ Gyrfalcon eyrie no. 7 1 , Seward Peninsula,
Alaska
Name
Ptarmigan species
Unidentified waterfowl
Pintails
TOTAL BIRDS
Ground squirrels
'l'OTAL MAMMALS
TOTAL KILLS
Number
36
ll
_l
43
_l-
3
46
Per cent
of kill
78.3
8.7
__§__0_
93.5
1 Eyrie no. 7 is located on a river bluff in a broad, marshy
valley 36 air~miles from the nearest coast.
'l'able 18b ·-. Gyrfalcon food remains from Table 18a grouped
in various major cRtegories
categ_?ry
Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Migratory birds subtotal
Ptarmigan
Ground squirrels
Microtines
Resident ipecies subtotal
t'tarmj,gan, .i aegers ,-and
( ground sq~irrels
Ptarmigan and ground
sql!i:t:_I'e 1~
Number
7
7
36
3
39
39
Per cent
of kill
15.2
15.2
78.3
6.5
81~ • 8
_ _g 4 • 8.
1 Figur~s f~r 1969 are calculated on the basis of 46 kills.
I
l
I
l
.I
Table 1.9a-. -·Gyrfalcon eyrie no. 8 1 , Se~-mrd Peninsula,
Alaska
-1968
99
Name Number
Per cent
of kill
Ptarmigan species
hfhimbrel
Short-eared Owl
Unidentified passerines
Unidentified bird
TO'l'AL BIRDS
-Ground squirrel
-TOTAL r·1AMMALS
TOTAL KILLS
54
2
2
l
l
60
4
4
6ll
84.4
3.1
3.1
1.6
1.6
93.8
6.3
1 Eyrie no. 8 is located on the shoulder of a ridge in a
-hig~ ba~ren valley system 32 air-miles from the near~st
coas.t ..
;.;·,H>f!l<'i~TY ilF
.~ ....... ,. .............. .-.. -------
u--"NIV. Oli' -AtASKA .. LlliRAH.Y
~ ~ i
I I ~
f.
I
i
I
l
I
I
i
i
i
I
i
100
Table 1.9b. Gyrfalcon food remains from Table 19a grouped
in various major categories
Category
Ducks·
Shorebirds
Passerines
Jaegers
Seabirds
Short-eared Owl
·-
Migrator~ bir~s subtotal
Ptarmigan
Ground squirrels
l'l!icrotines
Resirt~nt species sybtotal
Ptarmigan, jaegers, and
ground squirrels
~.P_tarJnigan and j aegers
Ptarmigan and ground
squirrels
Number
2
1
2
6
511
lj
58
58
Per cent
of kill
3.1
1.6
3.1
9 . 1~
8 4. lj
81! • l!
90.6 .
90.6
1 Figures-for 1968 are calculated on~the basis of 64 kills.
---· ... ---··
101
Table 20a. Gyrfalcon eyrie no. 9 1 , Seward Peninsula,
Alaska
Name
Ptarmigan species
Short-eared OvJl
Unidentified shorebirds
Pintail
Long-tailed Jaeger
TOTAL BIRDS
Arctic Ground Squirrel
Unidentified microtine
Mink
TOrr AL MAI\1MALS
TOTAL KILLS
1968
Per cent
Number of kill
153 93.9
3 1.8
2 1.2
1 0.6
159 97.5
2 1.2
1 0.6
1 0.6
4 2.4
163
1970
Pe-r cent
Number of kill
21 65.6
, 3.1 ..L
8 25.0 -·-
30 93.7
2 6.3
2 6.3
32
1 Eyrie no. 9 is located on a hillside in a broad vaJ.ley
system, 16 air-miles from the nearest coast.
102
Table 20b. Gyrfalcon foo0 ~~~~~~s ~rom Table 20a grouped
in various major categories
--------
Cater:;ory
-Ducks
Shorebirds
Passerines
Jaegers
Seabirds
S~10rt-t=;ared _Owl
I·Ur;rator,y b:Lrds
subtotal
Ptarmlgan
Ground squirrels
!:Jicrotlnes
Resident species
subtotal
P tarm]_gan, j aegers,
and ground squirrels
Ptarmigan and jaegers
Ptarmigan and ground
squirrels
Number ----
1
2
3
6
153
2
l --'-
157
155
Per cent
of klll
0.6
1.2
1.8
3.7
93.9
1.2
0.6
96.3
Number
J.
8
9
21
2
23
31
29
23
Per cent
of ldll
3.1
25.0
28.1
65.6
6.3
71.9
96.9
90.7
'71. 9
1 Fig~res for 1968 are calculated on the basis of l63 kills.
2--. -Flgures for 1970 are calculated on the basis of 32 kills.
103
'rabl-e 2la. Gyrfalcon eyrie no. 101 , Seward Peninsula,
Alaska
Name
Ptarmigan species
Unidentified waterfowl species
Unidentified sandpiper species
Unidentified passerines
TQ'r.AL BJ:RDS
Arctic Ground Squirrel
·collated Lemming· ·
Unidentified microtine
· TUr AL l'-1M!JivrALS · ·
'fOTAL KILLS
____ 1968
Number
11
l
1
1
3
2
1
11
25
Per cent
of klll
44.0
11. 0
4.0
4.0
56.0
32.0
8.0
11 • 0
ljll • 0
1 ~Eyr~e no. 10 is located high on the side of a river valley·
15 air~miles from the nearest coast.
. .
(
Table 2lb. Gyrfalcon food remains from Table 2la grouped
~n various major categories
Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Mi~ratory birds subtotal
Ptarmigan
Ground squirrels
rucrotj_nes
Hesj_dent species subtotal
Pta:r'migan, j aeg:,ers" and
ground squirrels
Ptarmigan and jaegers
· Ptor·rnigan and ground
squirrels ------
1968 1
----------~· -----------
Number
1
1
1
3
11
8
__]_
22
19
Per cent
of kill
4.0
4.0
4.0
12.0
44.0
32.0
12.0
88.0
76.0
1 Figures for l963 are calculated on the basis of 25 kills.
(
I
\
105
Table 22a. Gyrfalcon eyrie no. 11 1 , Seward Peninsula,
.Alaska
Natne Number
Ptarmigan species
TOTAL BIRDS
TOTAL KILLS 45
1970
Per cent
of ;.:J.ll
100.0
100.0
100.0
1 Eyrie no. 11 is located on a river bluff at the edge of the
central lowlands in a large drainage system 42 air-miles
from the nearest coast.
106
Table 22·b. Gyrfalcon food remains from Table 22a grouped
in various major cate~ories
Category
Duc:Ks .
Shor.ebirds
Passerines
·Ja~gers
Seabirds
Migratory birds subtotal
Ptarmigan.
Ground.squirrels
f·Hcrotines
'Resident species subtotal
Ptarmigan, jaegers\ and
~round squirrels
Pta~migan and jaegers
Ptarmigan and. gr.ound
squirrels
Number
Per cent
of kill
100.0
100.0
1 Fig.ures for· 1970 are calculated on the basis of 45 kills.
/-~,
~~~ -~----5
107
1
Table 2Ja. Gyrfalcon eyrie no. 12 , Seward Peninsula,
Alaska
Name
· Ptarmlgan species
Short~eared Ov1l
Long-ta~led Jaeger
TOTAL BIRDS
-Red-backed Vole
Lemming species
TOTAL MAMMALS
TOTAL KILLS
Number
62
2
1
3
l
11
69
1970
Per cent
of kj_ll
-89.9.
2.9
l. li
9 !J • 2
11_ 3
1.4
~ '7
-' • I
1 Eyrie no. 12 is lb6at~d ori a river bluff at the edge of
·-the central lowlands in a large drainage system 42 air-
miles from the nearest coast.
< ••• • 108
'l'able · 2-3b. · Gyrfalc·on · food renains from 'rable 2 3a p.;rouped
in various major categories
Category
·Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Sr1ort-eared 0\vl
f'ligratory birds subtotal
Ptarmigan
Ground squ~rrels
Microt·ines
Resident species subtotal
Ptarmigan, j~egers and
ground squirrels
. Ptarmigan and jaegers
Ptarmigan and grouod
squirrels
Number
1
2
3
62
lj
66
67
Per cent
of kill
1. lj
2.9 --·
4.3·
8'.L 9
-~
95. '[
97.1·
lFigures for 1970 are calculated on the bas'is of 69 k:!.lls
·?"..·-.:.
··-;· .. :-··
...
'l'able .~I~ a~. Gyrfalcon eyrie no. 13 1 , Set'Jard Peninsula,
A1flska
1970
109
Per cent
Name -
Ptarmi~an species
· Unident::tf1.ed birds
OldsquaN . -
American Clo}rlcr: Plover
common sn:l.pc.
Lesser Ycllowlegs
Lon€_~-ta:llr:d Jaer;er
•rree f>parr·ovr
SriOW Bun!~ tnr;--
Unidentified passerine
'l'O'f!\L BIRDS
Arctic Ground Squirrel
.'l'O'l'A L fv1Af1UiiALS~
Number
81~
10
1
1
1
1
1
1
1
1
102
_]_
7
109
of kill
77.1
9.2
0.9
0.9
0.9
0.9
0.9
0.9
0-.9--
__Q_:_.2_
93.5
6.4
\
6. lf
lEyri~ no.-13 is located high on the edge of a plateau
~ecion falling off to the coastal lowlands and 27 a1~~
miies from the rtearest coast • .
- - - - - - - -
(
i
\
.110
Table 24b. Gyrfalcon food remains from Table 24a grouped
in various major categories
Ducks·
Shorebirds
Passerines
Jaegers
Seabirds
Unidentified birds
Migratory birds subtotal
Ptarmigan
Ground squirrels
Microtines
Hesident specie.s subtotal
Ptarmigan, jaegers, and
ground squirrels
Ptarmigan_and jaegers
Ptarmigari and ground
squirrels
Number
1
3
3
·1
10
18
811
7
91
92
85
91
1970 1
Per cent
of kiJ.l
0.9
2.8
2.8
0.9
__ 9 -~
16.5 -
77.1
6.4
83.5
8 ~~ • 4
78.0
83.5
1 Figtires for 1970 are calculated on the basis of 109 kills.
-..:.; . -·~·
111
4 1 . Table ~5a. Gy~falcon eyrie no. 1 , Seward Penjnsula,
Alaska
1970
Per cent
Name Number of kill -----
Ptarmigan species 11 37.9
Unidentified passerines 3 10.3
Golden Plover 2 6.9
Common snipe 1 3.4
l.rlhimbrel 1 3. li
TOTAL BIRDS 18 61.9
Arctic Ground Squirrel 8 27.6
Collared Lemming 2 6.9
Lemming species l 3.4
TO'rAL MAMMALS ll 3'7. 8
TorrAL KILLS < 29
I
\
l __ .
llj located creek bluff in broad rela-t;yrie no. is on a a
· tively open valley system 17.5 air-miles from the nearest
coast.
(
-==------·--=~~ -------~ .~~
112
Table 25b. Gyrfalcon food remains from Table 25a grouped
in various major cate~ories
Categorv.
Ducl-;:s
Shorebirds
Passerines
_ .raegers
Seabirds
Migratory birds subtotal
Ptarmigan
Ground squirrels
i\Ucrotines
Resident species subtotal
Ptarmigan, jaegers, and
ground squirrels
Ptarr:;igan and j aegers
Ptarmigan and ground
squi:rrels
Number
3
3
7
ll
Q u
_]_
22
19
Per cent
of kill
10.3
10.3
21-t .l
'15. 9
2'7. 6
10.3
75.9
65.5
1 F'igures for 197 0 are calculated on the basis of 29 kiJ.ls.
----
Table 26a. Gyrfalcon eyrie no.
. Alaska
Name
Ptarmigan species
Urtidentified passerines
ADerican Golden Plover
Unidentified shorebirds
Lon~-tailed Jaeger
Snow Bunting
Unidentified birds
TO'l'AL DIRDS
Arctic Ground Squirrel
Lemming species
Collared Lemming
Vole species
TOTAL J'.1M/iMALS
Unidentified kill
TOTAL_UNIDENTIFIED KILLS
Tor.r AL KILLS
113
1
15 , Seward Peninsula,
Number
17
5
I[
1
1
J.
1
30
6
2
1
1
10
1
1
1970
Per cent
of kill
41.5
12.2
9.8
2 .li
2. ll
2 . L~
73.1
lil. 6
4.9
2,11
2 . )~
211 • 3
2 .11
2.4
1 Eyrie no. 15 is located hi~h on the side of a narrow creek
valley surro~nded by high ~ills 15 air-miles from the
coast.
---~-
/
'
(
\
llLJ
Table 26b. Gyrfalcon food remains from Table 26a grouped
in various major categories
·category
-Ducks
Shorebirds
Passerines
Jaegers
Seabirds
Unidentified birds
IV!igratory birds-subtotal
_Ptarmigan
Ground squirrels
f':Iicrotines
Resident species s~btotal
-Ptarmigan, jaegers, and
:_ ground sguirrels
Ptarmigan and jaegers
Ptarmigan and ground
squirrels
Number
5
6
1
1
13
17
6
4
27
2lJ
18
23
Per cent
of kill
12.2
14.6
2. l!
2.4
31.7
Jn .5
14.6
2~~
65.9
31.5
43.9
29.1
1 Figure& for 1970 are calculated on the basis-of 41 kills. -
---
"" ----..--·---·
115
Table 27a. Gyrfalcon eyrie no. 161 , Seward Peninsula,
Alaska
Name
Ptarmigan species
Common snipe
Unidentified passerines
Robin
Lapland Longspur
Bar-tailed Godwit
Unidentifi~d shorebirds
Say's Phobe
Varied Thrush
Water Pipit
Fox Sparrow
TO'r AL BIRDS
Arctic Ground Squirrel
Collared Lemming
_L_ernming species
Vole species
TOTAL l\1AMMALS
'l,OTAL KILLS
Number
27
3
3
2
2
]_
1
1
1
l
1
IJ3
25
lt
2
1
32
75
1970
Per cent
of kill
36.0
ILO
ILO
2.7
2.7
1.3
1.3
1.3
1.3
1.3
1.3
57.2
3 ? -. .J •. 5
).3
2.7
~
112. 6
1 Eyrie rio. 16 is located hi~h on the side of a broad river
valley 12 air-miles from the coast.
' -~
116
Table 27b. ·Gyrfalcon food reDains from Table 27a grouped
in various major categories
Cate~o~
.· IJucks
Shor·ebi rds
Passerines
.Jaegers
Seabirds
Migratory hirds subtotal
Ptarmigan
Ground squirrels
Microtj_nes
Resident species subtotal
Ptarmigan, jaegers; and
ground squirrels
Ptarmigan and ground
squirrels
Number
5
ll
16
27
25
_]_
59
52
-----
Per cent
of kill
21.3
36.0
33.3
9. 3_
"(8. 7
69 .11
1 Pi;-::_;ure-s f~r 1970 are calculated on the basis of 7·5 kills.
"
'The ran~;e 1 in the per cen·t occurrence and numbers of the three' ma,j or prey categories, migratory ·
bird species, and resident sp~cies at 23 Seward Peninsula Gyrfalcon ne~tings
1968 1969 1970
Pr-ey Ca';;egory Per cent Numbers Fer cent Numbers Per cent Numbers
_ _2.£_ G ro :1 12__ Ra:1:;;e Ranl\e Rans;e Ran~e Ran~e Ra:;'lr;e
Ptnrmi~a.n 21.1 j 93.9 8; 153 12.7; '(8.3 8· 37 16.5; 100.0 • 1 • 84 ' ~...~...,
Jat~·;_;,:?rs 8.0; 50.9 0. 28 0. 0; 12.0 0. 6 0. 0; 56.5 o· ,......,
' ' ·' C>c:
G:rouncl squirrels 1.2; 118. 4 1; 15 4. 0; (j 0 .. 3 1; 38 0.0; 33.3 0; 25
:'<Ugro. tory bird species 3. 7; 63.5 3; 33 15.2; ~53 .. 7 2; 22 0. 0; 80.0 0; llG
Resident species 35.5; 96.3 19; 157 1!6.3~ ()4 .. 8 9• .47 20.0~ 100.0 22; Ql .. ~
'l'OTAL NESTINGS 7 6 10
1 n11 arithmetic figures rep~esent the minimum and maximum values obtained from tables 12b through 27b.
=======================================================·--=====================================
1113
Larids, and Anatids, and that pairs nesting inland feed
primarily on ptarmigan (Dementiev and Gortchakovskaya,
1945; Cade, 1960). This suggests that Gyrfalcons will tend
to utilize those snecies that are the most abundant (i.e.,
available and therefore possibly the easiest to catch) in
the general vicinity of the Gyrfalcon nesting cliff. From
my data on the food habits of Gyrfalcon nesting on the
Seward Peninsula, it is apparent that pairs nesting on the
coast or in an area strongly influenced by the coastal
environment pr~y ~~on species associated with both the
coastal and the inland habitats (especially Larids, Alcids,
jae~ers, ground squirrels, and ptarmigan). In general, the
prey taken by a nesiing Gyrfalcon pair on the Seward Pcnin-
sula-reflects the habitat characteristics of the hunting
ranse of t11at pair such that pairs nesting in the vicinity
of a particular species !!concentration!! ''rill prey substan-
tially on that species. For examp~e, pairs (eyrie number~
one and four) nesting on the coast will take a substantial
nu~ber of jaegers, Alcids, and Larids compared with a pair
nesting in the uplands where ptar~igan and ground squirrels
11ill _predominate.
Little i8-kno1·m about pair or incli vidual prefer-
ence. It _is note-worthy that the nesting pair at the eyrie
des_ignated._::,_': 2" in the tables took large numbers of Lonr:;-
--
tailed ~~~~ers during a time when ~ock Ptarmigan were very
119
plentiful in the immediate vicinity of their nest (about 40
territorial male Rock Ptarmigan were in view of their nest-
ing cliff).
In 1969 this same pair (as judged by the color of
the members of the pair) accounted for at least six Long-
tailed Jaegers at a time when jaegers were much scarcer and
when ~1 oth~r nesting pairs of Gyrfalcons accounted for only
ten Long-tailed Jaegers (based on the prey remains).
Tables 12~,b ~o 27a,b describe a continuum of the
variability of Gyrfalcon prey over a large sample of eyries
in differing habitats and situations. It is possible to
fit ~ll pr~vious Gyrfalcon food studies reoorted in the
literature into this broad picture. A broad continuum of
situations exists ranging fron insular seabird eater~ to
interior ptarmigan/grotlnd squirrel eaters. This general
continuum will be affected,. for example, hy the nearness
of waterfowl habitat (Bengtson, 1971). Each general ar·ea
of G~~falcon nesting habitat can be defined by geographical
criteria {the existence of marshes, coast lines, rivers
and uplands, for example) and each of these areas will tend
to have its own general falcon/prey relationship. E8ch
Gyrfalcon pair, dependent upon their location in relation
to prey species, will produce a unifor~ dietary prey list,
but that.list will be strongly related to those p~cy spe-
cies T6~nd in the vicinity of the Gyrfalcons' nest. -su~h
120
a dietary list from one pair may or may not closely resem-
ble the dietary lists from other Gyrfalcon pairs depending
upon whether or not all the pairs are nesting in similar
habitat Situations.
SUMMARY AND CONCLUSIONS
1. Breedin~ Gyrfalcon populations on the Seward
Peninsula during the summers of 1968, 1969, and 1970 were
st~ble on a region-wide basis at a high level. Of 131
nestings observed, 311 occurred in 1968, lJ8 in 1969, and l.J9
in 1970. The low figure for 1968 reflects poor survey
-coverage in tha~ year.
2. Local shifting of populations within smaller
units of the peninsula occurred which were correlated witl1
prey abundance.
3~ Nesting-cliff tenacity 0as low. Over the
three summers only four per cent of the nest1ng sites were
oc~upied all three years. The interrelationships between
Rough-legg~d Hawks, Golden Eagles, and Ravens, all of
~hitih also utilize cliffs as nesting sites~ is complex anct
as yet p6brly ~nderstood.
4. Distribution on the peninsula is not uniform,
but controlled by the availability of nesting cliffs. Over
all three years 66 per cent of the observed nestings
occurred in only about 2,200 sauare miles of the peninsula
or approximately 13 per_cent.
5. Prey remains were collected from 37 nestings·
and 1,483 kills were identified, representing 32 species bf
birds and eight species of mammals. This is a considerably
121
. i
:
122
more diverse list of Gyrfalcon prey than has previously
been renorted.
6. Four species vJere of overriding importance:
Rock Ptarmigan, Willow Ptarmigan, the Arctic Ground
Squirrel, and the~Long-tailed Jaeger. These four made up
81 per cent by number and 92 per cent by weight of the
sample.
1. Prey utilization varie~ with availability
both temporally and spatially. ~~ile the four species
mentioned-above continued to be important during all summers,
it is apparent that Gyrfalcons readily
tions to members of a wide spectrum of other prey species
as availability dictates.
LITERATURE CI'l'F.D
Bengt~o~, Sveh~Axel. 1971. · Hunting methods and choice of
prey of Gyrfalcons Falco rusticolus at Myvatn in
northeast Iceland. Ibis, 113:~68-476.
Bond, R. M. 1936. Eating habits of falcons with special
reference to pellet analysis. Condor, 38:72-76.
Brown, Leslie, and Dean Amadon.
falcons of the world.
1968. Eagles, hawks, and
McGraw Hill, N.Y. 945 pp.
Brull, H. 1937. Das Leben de~tscher Greifvogel. Jena:
Gustav Fischer. Not seen.
Cade, T. J. 1960~ Ecology of the peregrine and Gyrfalcon
populations in Alaska. Univ. Calif. Publ. Zool.,
63:151-290.
Dementiev, G. P., and N. N. Gortchakovskaya.
biology pf the Norwegian Gyrfalcon.
559-565.
1945. On the
Ibis, 87:
Erring-ton, P ~ I.!; 1930. The pellet analysis Method of
raptor food habits study. Condor, 32:292-296.
1932. Technique of ~aptor fbod habits study.
Condor, 34:75-86.
Gudmundsson, Fir.nur. 1970, The predator-prey relationship
of the Gyrfalc6ri (Falco rusticolus) and the Rock
Pta~migan (Lagopus mutus) in Iceland. Excerpts
from the Abs~racts of the XV International Orni-
thological Congress. In Raptor Research News, 4:
178.
Hagen, Yngvar. l9S2. Tile g,y 1•..,-falcon
irr Dovre, Norway. Skrifter
Norske Videnskaps-Akademi.
No. 4.
(Falco rusticolus L.)
Utigitt av Det --
I. Mat-Naturv. Klasse,
Murie, A .. 1946. Observations on the birds of Mount
·.McKinley Nation~l Park, Alaska. · Coridor, 48:
253-261.
123
~ ~
I ~ t
I
I I
J
I
I
i
I
l
12lJ
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