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COLLISION POTENTIAL OF EIDERS AND OTHER BIRDS NEAR A
PROPOSED WINDFARM AT ST. LAWRENCE ISLAND,
OCTOBERNOVEMBER 2002
Prepared for
Ecological Services
U.S. Fish and Wildlife Service
605 W 4th Avenue, Room G62
Anchorage, AK 99501
and
Alaska Industrial and Development AuthorityAlaska Energy Authority
813 W Northern Lights Boulevard
Anchorage, AK 99503
Prepared by
Robert H. Day
John R. Rose
Robert J. Ritchie
John E. Shook
ABR, Inc.Environmental Research & Services
P.O. Box 80410
Fairbanks, AK 99708-0410
Brian A. Cooper
ABR, Inc.Environmental Research & Services
P.O. Box 249
Forest Grove, OR 97116-0249
March 2003
i St. Lawrence Island Eiders
EXECUTIVE SUMMARY
During spring and fall, many eiders pass St.
Lawrence Island during their passage between
breeding and wintering grounds. At those
times, they may collide with human-made
structures at the village of Gambell, on
northwestern St. Lawrence island. Because the
Alaska Industrial Development Authority
(AIDEA)/Alaska Energy Authority is planning
on installing a windfarm at Gambell, we were
hired to study bird movements in the vicinity
of Gambell and to evaluate the probability of
collision with the proposed windfarm,
especially the collision of endangered
Spectacled (Somateria fischeri) and Steller’s
(Polysticta stelleri) eiders.
The objectives of this study were to: (1) use
visual sampling and ornithological radar to
observe the migration and movements of
eiders and other bird species near Gambell
during late fall; (2) measure movement rates,
locations of movement, behavior, and flight
altitudes of eiders and other bird species near
Gambell during late fall; (3) collect
information on bird movements that could be
used to help site the proposed windfarm in
such a manner as to minimize the risk of bird
collisions; and (4) to evaluate the collision
potential for eiders at Gambell during late fall.
To complete these objectives, we conducted
surveys for eiders and other species at Gambell
in OctoberNovember 2002.
We recorded 876 groups of birds visually
(representing 26,172 birds) and 687 radar
targets of birds during this survey.
Frequent precipitation (rain) and high winds
(causing high swells at sea and extensive sea
clutter on the radar display) made radar
sampling impossible or difficult much of the
time. Consequently, we emphasized the visual
sampling but conducted radar sampling when
conditions allowed.
During visual sampling, movement rates were
dominated numerically (in decreasing order)
by alcids (almost entirely murres), eiders,
unidentified waterbirds, gulls (especially
Glaucous Gulls and Black-legged Kittiwakes),
other ducks (especially Long-tailed Ducks),
and cormorants. Eider movements consisted
of Spectacled, King, and Common eiders;
Steller’s Eider were not recorded.
Mean movement rates of total eiders observed
visually varied geographically, with all
recorded flying only over the ocean and none
flying over the mountain, the windfarm, or the
town. Almost all non-eider taxa were recorded
moving over the ocean, with raptors recorded
moving only over the windfarm and the town
and with only gulls recorded moving over all
four zones.
Mean flock sizes varied dramatically among
species and species-groups. The mean flock
size of eiders was 28.0 birds.
Mean flight altitudes also varied dramatically
among species and species-groups. The
highest mean flight altitude occurred in total
gulls, followed (in decreasing order) by
cormorants, raptors, unidentified waterbirds,
loons, other ducks, eiders, and alcids. Eiders
had a mean flight altitude of 1.8 m and a
maximal flight altitude of 15 m. Because
essentially all birds flew only over the ocean,
we were unable to examine whether mean
flight altitudes varied geographically.
Flight behavior of birds observed visually was
dominated overall by contouring flight (i.e.,
following the shoreline; ~64% of all flocks),
followed (in decreasing frequency) by
straight-line directional flight (~30% of all
flocks), erratic, flying/landing, and circling.
Because essentially all birds flew over the
ocean, we were unable to examine whether
flight behavior varied geographically.
The high seas recorded during this study and
the low flight altitudes of eiders resulted in an
underestimation of movement rates of that
group over the ocean with ornithological radar.
Although the number of eiders recorded by the
radar over the ocean was underestimated, the
radar did an excellent job of detecting targets
over land, which was an important aspect of
this study. The view over land was excellent
and was not affected by sea clutter. Therefore,
we considered the radar to provide an
underestimate of numbers of eiders moving
over the ocean but to provide an accurate
St. Lawrence Island Eiders ii
estimate of numbers of eiders moving over
land.
"Eiders" exhibited low mean movement rates
on radar during most dates and under most
weather conditions, with most means
averaging 13 targets/h. "Non-eiders"
exhibited mean movement rates that were ~20
times larger than those for "eiders," with most
means averaging ~25 targets/h.
Mean movement rates of "eiders" were ~175%
higher at night than during the day, whereas
mean movement rates of "non-eiders" were
~160% higher during the day than at night
(primarily because of all of the daytime gull
movements).
Mean movement rates of "eiders" on radar
varied geographically, with essentially all birds
flying only over the ocean and none flying
over the mountain and town, similar to what
was recorded visually. We believe that the one
"eider" target recorded flying over the
proposed windfarm was not that of not eiders.
Mean movement rates of "non-eiders" also
varied geographically, with none recorded over
the mountain, moderate numbers moving over
the proposed windfarm and town, and much
higher numbers moving over the ocean.
"Eiders" were recorded on radar exhibiting
three of the five standardized behaviors,
although ~90% of all "eider" targets flew with
straight-line directional characteristics.
"Non-eiders" exhibited all five of the
standardized behaviors, with ~60% of all
"non-eider" targets flying with straight-line
characteristics and another 34% flying by
contouring (i.e., following the shoreline).
We recorded no bird mortality at either the
FAA towers or the meteorological tower.
Both the radar and visual data indicate that the
number of birds moving and wintering in this
area is large: we saw a total of >26,000 birds
during our visual sampling, with an overall
mean daily movement rate of 700 birds/h.
The visual data indicate that eiders form a
significant proportion of the birds seen near
Gambell at this time of the year, representing
24.542.9% of all birds.
Both the daytime visual and daytime and
nighttime radar-movement data indicate that
most birds passing Gambell in the fall do so
over the ocean, with very little movement over
land, including the proposed windfarm
(primarily gulls and raptors). Although we
saw no eiders or waterfowl of any species
flying over land, local villagers informed us
that eiders and Long-tailed Ducks fly over the
spit on which Gambell occurs after the sea
freezes and snow obscures the boundary
between sea and land. At those times, these
birds "cut the corner" over the spit while
moving back and forth as polynyas open and
close on the northern and southern sides of the
island. Local villagers told us that, when these
birds do cross the spit, they occasionally hit the
FAA towers.
The flight-altitude data indicate that flight
altitudes of most species over the ocean are so
low that, unless they change altitude as they
cross land, they would pass under the rotor
blades of the turbines as they are envisioned at
this time.
The behavioral data indicate that, because most
of the birds seen in this study fly by contouring
(i.e., following the shoreline), those birds
flying over the ocean will have little chance of
hitting wind turbines. On the other hand, if a
flock of eiders does deviate to cross over the
spit, the other members of the flock will
follow, resulting in a low probability of
collision but a high probability of substantial
mortality if a collision does occur.
Although summer bird movements were not
studied, we suggest that the location of the
auklet colony should be a consideration in site
selection at this windfarm.
iii St. Lawrence Island Eiders
TABLE OF CONTENTS
EXECUTIVE SUMMARY............................................................................................................................i
LIST OF FIGURES......................................................................................................................................iii
LIST OF TABLES........................................................................................................................................iii
ACKNOWLEDGMENTS............................................................................................................................iv
INTRODUCTION.........................................................................................................................................1
STUDY AREA..............................................................................................................................................1
METHODS....................................................................................................................................................3
DATA COLLECTION ...............................................................................................................................3
VISUAL ...................................................................................................................................................5
RADAR....................................................................................................................................................5
MORTALITY ..........................................................................................................................................7
DATA ANALYSIS.....................................................................................................................................7
VISUAL ...................................................................................................................................................7
RADAR....................................................................................................................................................8
MORTALITY ..........................................................................................................................................9
RESULTS......................................................................................................................................................9
VISUAL......................................................................................................................................................9
MOVEMENT RATES.............................................................................................................................9
FLOCK SIZE .........................................................................................................................................14
FLIGHT ALTITUDE.............................................................................................................................14
FLIGHT BEHAVIOR............................................................................................................................14
RADAR.....................................................................................................................................................14
RADAR EFFICACY AND TARGET IDENTIFICATION..................................................................14
MOVEMENT RATES...........................................................................................................................24
FLIGHT BEHAVIOR............................................................................................................................24
AVIAN MORTALITY...........................................................................................................................28
DISCUSSION..............................................................................................................................................28
CONCLUSIONS AND RECOMMENDATIONS......................................................................................29
LITERATURE CITED................................................................................................................................29
LIST OF FIGURES
Figure 1. Study area at Gambell, St. Lawrence Island, showing locations of radar and visual
sampling sites, movement zones, towers and tower search area, and the proposed
windfarm in fall 2002 ...............................................................................................................2
LIST OF TABLES
Table 1. Hours sampled by radar and/or visual observers, Gambell, Alaska, 23 October2
November 2002, by date...........................................................................................................4
Table 2. Results of ground-based searches for dead birds in the vicinity of the FAA and
meteorological towers near Gambell, Alaska, 23 October3 November 2002........................8
Table 3. Movement rates of birds recorded visually near Gambell, Alaska, 23 October2
November 2002, by species/species-group and date; because so many taxa were seen,
data are presented only for all eider species and for all species-groups.................................10
St. Lawrence Island Eiders iv
Table 4. Movement rates of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group and movement zone; because so many taxa were seen,
data are presented only for all eider species and for all species-groups.................................13
Table 5. Flock sizes and flight altitudes of birds recorded visually near Gambell, Alaska, 23
October2 November 2002, by species/species-group...........................................................15
Table 6. Flight altitudes of birds recorded visually near Gambell, Alaska, 23 October2
November 2002, by species/species-group and movement zone ...........................................16
Table 7. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2
November 2002, by species/species-group.............................................................................18
Table 8. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2
November 2002, by species/species-group and movement zone ...........................................19
Table 9. Efficiency of detection of eider radar targets near Gambell, Alaska, 23 October3
November 2002, by sampling session....................................................................................23
Table 10. Movement rates of birds recorded migrating on radar near Gambell, Alaska, 23
October2 November 2002, by species-group and factor......................................................25
Table 11. Movement rates of birds recorded on radar near Gambell, Alaska, 23 October2
November 2002, by species-group, factor, and movement zone............................................26
Table 12. Flight behavior of birds recorded on radar near Gambell, Alaska, 23 October2
November 2002, by species-group.........................................................................................26
Table 13. Flight behavior of birds recorded on radar near Gambell, Alaska, 23 October2
November 2002, by species-group and movement zone........................................................27
ACKNOWLEDGMENTS
Funding for this study came from the Endangered Species office of the U.S. Fish and Wildlife
Service, Anchorage, and the Alaska Energy Authority, Anchorage. We thank Greg Balogh, Dennis
Meiners, and Thomas Rothe of those organizations, respectively. At St. Lawrence Island, we were given
permission to conduct studies by Sivuqaq, Inc. (the village corporation of Gambell), the Native Village of
Gambell Village Council, and the City of Gambell; we thank Merle Apassingok (Chairman and CEO of
Sivuqaq), Gerald Soonagrook, Jr. (President of the Village Council), and Jason Nowpakahok (Mayor) of
those organizations. We also thank Preston Apangalook (City Manager) and elder Winfred James
(Vice-Mayor). Hansen Irrigoo and Rodney Unwiluk, both of Sivuqaq, Inc., were very helpful in arranging
our lodging and other logistics while staying in Gambell. At ABR, we thank Thomas DeLong for fiscal
oversight, Doris Armijo for logistics, Allison Zusi-Cobb for graphics, and Jennifer Roof for document
processing. This report has been improved by the reviews of Brian Cooper.
Introduction
1 St. Lawrence Island Eiders
INTRODUCTION
During spring and fall migration, many
Common (Somateria mollissima) and King (S.
spectabilis) eiders pass St. Lawrence Island during
their passage between breeding and wintering
grounds (Fay and Cade 1959). In addition, smaller
numbers of Spectacled (S. fischeri) and Steller’s
(Polysticta stelleri) eiders, both of which have
undergone population declines and currently are
protected by the Endangered Species Act, move
through the same area (USFWS 1996, 2002).
Counts of birds passing Barrow indicate that
Common and King eider populations also are
declining (Suydam et al. 2000), and there is
concern that populations of these species will
decline so much that they also will need protection
under the Endangered Species Act.
Eiders are thought to be susceptible to
collision with human-made structures because they
fly at low altitudes (Thompson and Person 1963,
Johnson and Richardson 1982; Day et al. 2001,
2002) and fly rapidly (Day et al. 1998, 2001,
2002), making collision avoidance difficult.
Indeed, they frequently have been recorded
colliding with human-made structures, including
boats (Dick and Donaldson 1978; John L. Sease,
National Marine Mammal Laboratory, Seattle, WA,
pers. comm.), streetlights and other bright lights
(John J. Burns, Alaska Department of Fish and
Game [retired], Fairbanks, AK, pers. comm.;
Patricia Kaminsky, University of Alaska/Seward
Marine Station, Seward, AK, pers. comm; Lori T.
Quakenbush, Alaska Department of Fish and
Game, Fairbanks, AK, pers. comm.), buildings
(James Short, ARCO, Anchorage, AK, pers.
comm.), and powerlines (Dean Kulowiyi,
Savoonga, AK; fide G. Balogh, USFWS,
Anchorage, AK). Waterfowl commonly collide
with man-made structures (e.g., Anderson 1978,
Dick and Donaldson 1978) and have been recorded
colliding with wind turbines (Erickson et al. 2001),
indicating that they are susceptible to this sort of
mortality.
The Alaska Energy Authority (AEA) is
planning to construct a series of windpower
energy-generation fields (windfields) throughout
northwestern Alaska to provide lower-cost energy
than presently is available to inhabitants of small
rural villages (D. Meiners, AEA, Anchorage, AK,
pers. comm.). So far, they have constructed
windfields in Kotzebue and Wales and plan to
construct windfields at Gambell, Hooper Bay, and
possibly other locations in western Alaska. Some
of these proposed windfields occur in locations
where migrating birds may collide with the wind
turbines. Gambell village, which is located on
western St. Lawrence Island, is a site where
endangered Spectacled Eiders pass during
migration and winter (Fay and Cade 1959,
Petersen et al. 1995, 1999) and, hence, is one
of those sites where collisions between
endangered Spectacled Eiders (and other
eiders) and wind turbines may occur. At this
time, however, knowledge of the migration
and movements of eiders and other birds and
of the variability in migration and movements
of these birds in the immediate vicinity of St.
Lawrence Island is limited.
This study was conducted in
OctoberNovember 2002 to learn more about the
migration and movements of eiders and other
species near Gambell, Alaska, and to evaluate
potential locations for a proposed windfarm near
that village. The objectives of this study were to:
use visual sampling and ornithological
radar to observe the migration and
movements of eiders and other bird species
near Gambell during late fall;
measure movement rates, locations of
movement, behavior, and flight altitudes of
eiders and other bird species near Gambell
during late fall;
collect information on bird movements
that could be used to help site the proposed
windfarm in such a manner as to minimize
the risk of bird collisions; and
to evaluate the collision potential for eiders
at Gambell during late fall.
STUDY AREA
St. Lawrence Island is the largest island in the
Bering Sea, lying ~320 km (~200 mi) south of
Bering Strait (Fig. 1). It has an area of ~4,500 km†
(~2,000 mi†) and consists of highly varied
topography, from mountains to saltwater lagoons.
The island’s primary habitat is tundra, with
scattered unvegetated, rocky areas. Mys (Cape)
Study Area
St. Lawrence Island Eiders 2 Figure 1.Study area at Gambell, St. Lawrence Island, showing locations of radar and visual sampling sites, movement zones, towers and tower search area, and the proposed windfarm in fall 2002.Chukchi SeaSaintLawrenceIslandGulfofAlaskaBering Sea######*100200300400500600614RadarSamplingSiteCape Visual SiteMidwayVisual SiteSouthernFAA TowerMeteorologicalAntenna**Northwest CapeG a m b e l lProposedWindfarmSevuokukMountainNorthernFAA TowerMOUNTAINWINDFARMTOWNOCEANOCEANTroutman LakeGambellSavoongaAtuk Mt.B e r i n g S e aB e r i n g S e aNiyrakpakLagoonPowooiliakBayStudy Site*SaintLawrenceIslandABR file:St_Lawrence_Island_Radar_02-182.mxd;23 December 2002500 0 500 Feet100 0 100 Meters5Elevations in feetLegendMovement Zone:WINDFARMExisting towerSearch area for dead birdsSampling or visual site#
Methods
3 St. Lawrence Island Eiders
Chaplina, a point on the southeastern Chukchi
Peninsula of Russia, lies ~65 km (~40 mi) from the
northwestern end of St. Lawrence Island. Sea ice
usually forms around the island in late November
(Fay and Cade 1959). Wind and fog are common,
and precipitation occurs ~300 days/year
(Alaska Community Database, available at
www.dced.state.ak.us/cbd/commdb/CF_BLOCK.
cfm).
The village of Gambell is a small,
predominantly Native community (Siberian
Yup’ik) of ~650 individuals located on a gravel spit
at the northwestern corner of the island (Fig. 1;
Alaska Community Database). The town abuts the
western side of Sevuokuk Mountain, which
contains an enormous auklet nesting colony during
the summer (BØdard 1969b). South of town lies
Troutman Lake, where gulls often congregated.
The proposed windfarm is located northeast of
town, inland from the ocean and just west of
Sevuokuk Mountain (Fig. 1). The proposed
windfarm will consist of 510 turbines with hub
heights of 24, 30, or 40 m above ground level (agl)
and rotor diameters 15 m or 20 m; at this time, the
exact specifications of the windfarm have not been
finalized (D. Meiners, AIDEA/Alaska Energy
Authority, in litt.).
The study area consisted of two visual
sampling sites, the radar sampling site, the
proposed windfarm, and the existing antenna field
that was searched for dead birds. The Cape visual
site was the primary visual site, whereas the
Midway site was secondary and was sampled only
two days. The antenna field consisted of two FAA
towers each ~23 m (~75 ft) high with a horizontal
wire strung between them; the towers were guyed
with 2 layers of 3 wires each. In addition, a nearby
meteorological antenna ~6 m (~20 ft) high was
guyed with 1 layer of 3 wires. We situated the
radar sampling site ~5070 m west of the FAA
towers and ~100120 m southwest of the landfill.
The site was in a trough between 34-m-high
gravel dunes.
Information on the avifauna of St. Lawrence
Island may be found in Friedmann (1932), Fay and
Cade (1959), Fay (1961), Sauer and Urban (1964),
Sealy et al. (1971), Johnson (1975), and Thompson
(1967). Information on seabirds at St. Lawrence
Island may be found in BØdard (1969a, 1969b),
Sealy and BØdard (1973), Sealy (1975, 1981), Piatt
et al. 1990a, 1990b). Information on waterfowl at
St. Lawrence Island may be found at Fay (1961)
and Petersen et al. (1995, 1999).
METHODS
We collected data on the movements,
behavior, flight altitudes, and mortality of
migrating eiders and other birds between 23
October and 3 November 2002 (Table 1). A severe
storm delayed our arrival on the island, eliminating
one day of sampling. In addition, sampling time
during the first two days was limited because of
time spent on coordinating with local organizations
about the study, on selection of sampling locations,
and on setup of the radar unit. Hence, the data
were collected over essentially a 9-day period. We
sampled for ~8 h/day with both visual equipment
(both 10X binoculars and night-vision equipment
with a 5X eyepiece) and ornithological radar (when
possible). We also checked the vicinity of the FAA
and meteorological towers for dead birds on a daily
basis, and often several times a day.
DATA COLLECTION
When possible, we collected visual and radar
data concurrently, so that we could use the radar to
help the visual observer locate birds for
identification and data collection. In return, the
visual observer provided information to the radar
operator on the identity of individual targets.
Although we attempted to sample concurrently at
all times, rain often prevented us from collecting
radar data (Table 1).
We attempted to collect data during 25-min
sessions for both sampling methods; we then used
5-min breaks between sessions to collect weather
data and to give observers a short break. Actual
lengths of sampling sessions were 25 min for
visual data and 625 min for radar data, with
nearly all sessions of both types being 25 minutes
long. We conducted a total of 47.00 h of visual
data collection on 92 sampling sessions and a total
of 29.25 h of radar data collection on 60 sampling
sessions. We lost another 54.50 h of radar
sampling time and another 18.00 h of after-dark
visual sampling time because of precipitation.
We recorded the following weather and
environmental data at the beginning of each
sampling session:
Methods
St. Lawrence Island Eiders 4
Table 1. Hours sampled by radar and/or visual observers, Gambell, Alaska, 23 October2 November
2002, by date.
Sampling method
Radar Visual
Date Begin End Sampled Rained
out
Begin End Sampled Rained out
23 OC 0 0 1900 2030 1.50 0
24 OC 1900 2200 0 3.00 1900a 2200a 1.00a 2.00
25 OC 1050 1240 1.50 0 1050 1240 1.50 0
1330 1615 2.75 0 1330b 1630b 3.00b 0
2030 2330 0 3.00 2030 2330 0 3.00
26 OC 1130 1140 0.17 0 1130 1430 3.00 0
1140 1430 0 3.00
1830 2030 0 2.00 1830 2030 2.00 0
2030 2330 0 3.00 2030 2330 0 3.00
27 OC 0800 1315 0 5.25 1015 1315 3.00 0
1530 1800 0 2.50 1530 1800 2.50 0
28 OC 0730 0800 0 0.50 0 0
1015 1245 0 1.50 1015 1245 2.50 0
1600 1830 0 2.50 1600 1830 2.50 0
2030 2330 0 3.00 2030 2330 0 3.00
29 OC 1000 1245 0 2.75 1015 1245 2.50 0
1500 1745 0 2.75 1515 1745 2.50 0
1900 2230 0 3.50 1900 2230 0 3.50
30 OC 1000 1330 0 3.50 1030 1330 3.00 0
1530 1745 0 2.25 1545 1745 2.00 0
1900 2230 0 3.50 1900 2230 0 3.50
31 OC 0800 1000 2.00 0
1200 1545 3.75 0 1200 1545 3.75 0
1800 1900 1.00 0 1800 1900 1.00 0
1900 2100 2.00 0
1 NO 0600 0900 0 3.00 1000 1315 3.25 0
1300 1600 0 3.00
1000 1300 3.00 0
1600 1800 2.00 0 1600 1800 2.00 0
1800 2100 3.00 0
2 NO 0745 1300 5.25 0 1015 1315 3.00 0
1700 1800 0 1.00 1700 1830 1.50 0
1800 2100 3.00 0
Total 29.25 54.50 47.00 18.00
a Included 1 h of concurrent sampling at the Midway visual site (19002000).
b Included 1 h of concurrent sampling at the Midway visual site (15001600).
Methods
5 St. Lawrence Island Eiders
wind speed (10 categories)calm,
15 mi/h (18 km/h), 610 mi/h
(916 km/h), 1115 mi/ h (1724 km/h),
1620 mi/h (2532 km/h), 2125 mi/h
(3340 km/h), 2630 mi/h (4148 km/h),
3135 mi/h (4956 km/h), 3640 mi/h
(5764 km/h), >40 mi/h (>64 km/h);
ordinal wind direction (10 catego-
ries)calm, north, northeast, east,
southeast, south, southwest, west,
northwest, variable/erratic;
cloud cover (to the nearest 5%);
ceiling height (10 ca tegories)0 m above
ground level (agl), 150 m, 51100 m,
101150 m, 151500 m, 5011,000 m,
1,0012,500 m, 2,5015,000 m, >5,000 m,
clear sky;
minimal distance able to see in a cardinal
direction (7 categories)050 m,
51100 m, 101500 m, 5011,000 m,
1,0012,500 m, 2,5015,000 m, >5,000 m;
light condition (6 categories)daylight
with or without precipitation, crepuscular
(twilight) with or without precipitation,
darkness with or without precipitation;
precipitation (11 ca tegories)none, fog,
drizzle, light rain, heavy rain, scattered
showers, sleet, snow, hail, mixed
rain/sleet/ snow, snow flurries;
minimal visibility (2 categories)poor
(<500 m), good (≥500 m);
air temperature (to the nearest 1 °C); and
moon visible to an observer on the ground
(2 categories)no, yes.
VISUAL
During the 12 days of sampling, we were able
to collect visual data during a total of 92 sampling
sessions (Table 1). The emphasis of the visual
sampling was on identifying birds, quantifying
flight altitudes, and determining the flight location.
The sampling unit was a flock of birds, regardless
of size.
We collected the following data on each bird
or flock of birds seen:
time;
identification, to lowest practical taxon;
flock size;
ordinal flight direction (9 catego-
ries)north, northeast, east, southeast,
south, southwest, west, northwest,
variable/erratic;
general flight behavior (4 catego-
ries)straight-line, erratic, circling,
landing on/taking off from the water;
lowest flight altitude (estimated to the
nearest 1 m agl/asl [above ground
level/above sea level] when flying ≤25 m
agl/asl, in 5-m increments from 26 to 50 m
agl/asl, in 10-m increments from 51 to
100 m agl/asl, and in 25-m increments
above 100 m agl/asl), with the emphasis on
altitude as the birds crossed an EastWest
line running through Northwest Cape;
island-passing flight behavior (6 catego-
ries)change in flight altitude, change in
flight direction, change in both, change in
neither, flaring, contouring (following the
shoreline) as the birds passed the island
and/or crossed the EastWest line; and
movement zone (4 categories; see Fig.
1)mountain (over Sevuokuk Mountain),
windfarm (over the proposed windfarm),
town (over the town or elsewhere over the
spit), ocean (only over the ocean north
and/or west of the spit).
Migrating eiders sometimes travel in long,
undulating strings that exhibit both lateral and
vertical motion (Day et al. 2001, 2002). Although
there is lateral motion, the flocks clearly exhibit a
strongly directional component of flight. As
described below for radar sampling, that strongly
directional movement of eider flocks is what we
are referring to with the term "straight-line flight."
The vertical undulations are fairly irregular but
generally do not vary by more than 10 m. Hence,
we considered a "significant" change in flight
direction or flight altitude as one that is more
extreme than these regular undulations.
RADAR
We monitored movements of birds with an
ornithological radar, described in Cooper et al.
Methods
St. Lawrence Island Eiders 6
(1991). This Furuno FCR-1411 surveillance radar
is a standard X-band radar transmitting at
9,410 MHz with a peak power output of 10 kW.
The range of this radar was set at 1.5 nm
(~2.8 km), the pulse setting was 0.60 sec, and
targets were plotted every 15 sec. The radar
laboratory (i.e., where the radar display was
located and where we collected the data) was a
small portable tent. We mounted the radar’s
antenna on a portable tripod near the northwestern
corner of the island (Fig. 1). We located this
antenna in a depression between 1012-ft-high
gravel dunes, providing an excellent radar fence
(see Eastwood 1967) that eliminated much, but not
all, of the sea clutter and most ground clutter
(energy that is reflected from the ground,
surrounding vegetation, waves on the sea, and
other objects that surround the radar unit).
The radar scanned a 360 arc and was used to
obtain information on flight paths, movement rates,
and behavior of birds. This radar has a digital
color display with several scientifically useful
features, including color-coded echoes (to
differentiate the strength of return signals) and
on-screen plotting of a sequence of echoes (to
depict flight paths). (An echo is a picture of a
target on the radar display screen; a target is one or
more birds displayed as a single echo on the radar
display screen. Flocks of birds typically appear as
a single echo, because the individual birds are
flying too closely to one another for the radar to be
able to differentiate them.)
During sampling, we were able to collect
radar data during a total of 60 sampling sessions,
with ~36 sessions completely lost because of heavy
precipitation (rain or snow) and/or heavy sea
clutter, both of which obscured bird-caused echoes.
The emphasis of the radar sampling was on
quantifying the number of flocks of birds flying
within specified zones and on describing aspects of
the behavior of those flocks of birds. The sampling
unit was a radar echo on the display screen (i.e., a
flock of birds, regardless of its size).
We collected the following data on each target
echo seen on the radar display screen:
time;
target type (2 categories)"eiderlike,"
"non-eiderlike" (see below);
general flight behavior (5 catego-
ries)straight-line (highly directional,
with long stretches of straight-line
movements), erratic (may or may not be
directional; often moved so erratically,
especially toward the end of the line
examined, that we could not predict with
confidence where the target was going),
circling (rarely directional and showing
evidence of circling the island), landing
on/taking off from the water, contouring
(following the coastline); and
movement zone (4 categories; see Fig.
1)mountain (over Sevuokuk Mountain),
windfarm (over the proposed windfarm),
town (over the town or elsewhere over the
spit), ocean (only over the ocean north
and/or west of the spit).
We also collected other data with the radar
(e.g., velocity, flight direction), but they
are not presented in this report.
An "eiderlike" target on radar was flying with
fairly specific characteristics. Eiders tend to fly in
tight flocks that, depending on the scale, may
exhibit lateral and vertical motion. On the radar
display screen, their echoes generally are large and
rapidly flying. At Barrow, 95% of all targets
visually confirmed as eiders were flying
4060 mi/h (6496 km/h), only 1.4% were flying
as slowly as 35 mi/h (56 km/h), and the targets had
mostly directional flight behavior (Day et al.,
unpubl. data). "Non-eiderlike" targets were
represented by all other flight characteristics and
ranged between small and large sizes, slow and fast
speeds, and variable directions (also see Day et al.
1998, 2001, 2002). When possible, however, we
determined visually the species and number of
birds represented by the radar echo.
The term "straight-line, directional flight" also
needs further explanation in the context of eider
behavior. As indicated above, eiders may fly in
long, undulating strings of birds that exhibit lateral
motion. Although these flocks exhibit somewhat
variable (i.e., possibly erratic) flight behavior at a
small scale, they almost always are strongly
directional at a larger scale (e.g., see Richardson
and Johnson 1981; Day et al. 1998, 2001, 2002).
The scale at which we were sampling was
Methods
7 St. Lawrence Island Eiders
intermediate between these two scales, so we
sometimes could see small undulations in radar
flightlines, but the flightlines almost always were
strongly directional overall. It is for this sense of
overall directional movement that we use the term
"straight-line."
MORTALITY
We searched the vicinity of the FAA towers
and the meteorological tower for the presence and
species-composition of dead birds 13 times/day,
for a total of 21 surveys (Table 2). The search area
was an irregularly shaped polygon that roughly
transcribed the area encompassed by the towers
(Fig. 1); it was ~9,500 m
†, or ~1 ha (~2.4 ac), in
area. Because the searches were conducted in an
area entirely covered with gravel, we assume that
all dead birds that were present were located by the
searchers. The first search of the day almost
always occurred during the morning, although 2 of
12 searches first occurred in the afternoon or
evening.
DATA ANALYSIS
We pooled both visual and radar data into
species-groups and other groupings to increase
sample sizes for analyses. For visual analyses, we
used individual species and the species-groups (1)
loons (= Pacific Loon [Gavia pacifica] +
unidentified loon); (2) cormorants (unidentified
cormorants; all almost certainly were Pelagic
Cormorants [Phalacrocorax pelagicus]); (3) eiders
(= Spectacled Eider + King Eider + Common Eider
+ unidentified eider); (4) other ducks
(= White-winged Scoter [Melanitta fusca] +
unidentified scoter + Long-tailed Duck [Clangula
hyemalis] + unidentified duck); (5) raptors
(= Gyrfalcon [Falco rusticolus] + Common Raven
[Corvus corax]); (6) shorebirds (= unidentified
phalarope); (7) gulls (= Glaucous Gull [Larus
hyperboreus] + Black-legged Kittiwake [Rissa
tridactyla] + Sabine’s Gull [Xema sabini] +
unidentified gull); (8) alcids (= Common Murre
[Uria aalge] + unidentified murre + Pigeon
Guillemot [Cepphus columba] + unidentified
guillemot); and (9) waterbirds (unidentified
waterbirds, being birds seen at a great distance and
being murres and/or ducks). For radar analyses,
we used (1) "eiders" (= targets that were identified
visually as eiders + targets that were identified
visually as unidentified waterbirds + unidentified
eiderlike targets); and (2) "non-eiders" (= targets
that were identified visually as non-eiders +
unidentified non-eiderlike targets). In the radar
section of the report, we first present data on all
taxa to see whether they potentially could be
misidentified as eiders, then concentrate on two
species-groups: "eiders" and "non-eiders."
Although flight characteristics of geese (especially
Brant) on radar are similar to those of eiders (Day
et al. 1999, 2001), we recorded no geese during
this study.
In data summaries and analyses, we examined
the data in terms of two visibility types, both of
which have been shown to affect movements
and/or collision rates of migrating birds. We
examined the effects of time of day after pooling
all light-condition samples from daytime and
crepuscular periods into "daytime" and retaining
all samples from nighttime periods as "nighttime."
We examined the effects of precipitation level
after pooling the light-condition categories into "no
precipitation" and "precipitation." We also
examined the effects of wind type on movements
of birds on the radar screen, since it also has been
recorded affecting bird migration and/or collision
rates. We assumed that all eiders and most other
birds would be heading to the southwest, past St.
Lawrence Island. Hence, we assumed that winds
blowing from the south, southwest, or northwest
would represent a headwind, those blowing from
the north, northeast, or east would represent a
tailwind, those from the northwest and southeast
would represent a crosswind, and no winds would
represent calm conditions. During this study, we
recorded only tailwinds and crosswinds.
We used the software SPSS and Microsoft
Excel for all analyses and data summaries.
Because the data showed such extreme differences
(see Results), we concluded that statistical tests
were irrelevant. Hence, we simply summarized the
data and discussed them without conducting
statistical tests.
VISUAL
We calculated mean, SE, and range in
movement rates (birds/h) of birds by date and
movement zone. To calculate these estimates, we
first divided the total number of birds in each
species and species-group by the number of
Methods
St. Lawrence Island Eiders 8
minutes sampled to derive an estimate of birds/h
for each sampling session. Because of the large
number of bird species involved, we present the
data only for individual eider species and for
species-groups for this parameter.
We calculated mean, SE, and ranges in flock
sizes of species and species-groups across all data.
We also calculated mean, SE, and range in minimal
flight altitudes of flocks of species and
species-groups overall and by movement zone.
We summarized the data on general flight
behavior of species and species-groups into the
four behavioral categories (straight-line, erratic,
circling, flying/landing), plus the contouring
behavior in the island-passing behavior category,
both altogether and by movement zone. We
counted the number of flocks exhibiting each
behavior, then converted those numbers to
percentages.
RADAR
We first tabulated counts of numbers of
targets of each species-group recorded during each
sample. These counts then were converted to
estimates of movement rates (targets/h), based on
the number of minutes sampled. Because heavy
precipitation sometimes obscured significant
portions of the screen (Table 1), we subtracted that
time from the 25-min sampling period and used the
resulting actual number of minutes sampled in the
calculation of movement rates. We calculated
mean – SE movement rates by date, time of day,
precipitation level, wind type, and movement zone
for each species-group.
For flight behavior, we first summarized the
flight-behavior data for each species-group into the
five behavioral categories (straight-line, erratic,
circling, flying/landing, contouring) by visibility
Table 2. Results of ground-based searches for dead birds in the vicinity of the FAA and meteorological
towers near Gambell, Alaska, 23 October3 November 2002.
Date Time Comments
23 October 1845 no birds found
24 October 1015 no birds found
25 October 1230 no birds found
26 October 1115 no birds found
1815 no birds found
2045 no birds found
27 October 0730 no birds found
28 October 0715 no birds found
2030 no birds found
29 October 0730 no birds found
1000 no birds found
30 October 0700 no birds found
1800 no birds found
31 October 0730 no birds found
1800 no birds found
1 November 0700 no birds found
1300 no birds found; dense fog
2030 no birds found; dense fog
2 November 1300 no birds found
1900 no birds found
3 November 1030 no birds found
Results
9 St. Lawrence Island Eiders
category, wind type, and movement zone. We
counted the number of instances of each behavior,
then converted the counts into percentages.
MORTALITY
We simply summarized the results of each
check for bird mortality in a table. We did not
conduct any statistical analyses on the data.
RESULTS
We recorded 878 groups of birds visually but
excluded 2 flocks of passerines (McKay’s
Buntings, Plectrophenax hyperboreus) from
analyses. The remaining 876 flocks represented a
total of 26,172 birds. One taxon that was
particularly difficult to identify well was what we
called "unidentified waterbirds," which were birds
flying so far offshore that we could not see them
well enough for identification. They consisted of
eiders, Long-tailed Ducks, and/or murres.
We also recorded 687 radar targets of birds
during this survey. Of the radar targets, we
recorded 42 that we considered to be those of
eiders, either being identified visually as eiders or
being unidentified visually but having eiderlike
flight characteristics. We also recorded 645
non-eider targets that either were identified
visually as non-eiders or were unidentified visually
but having non-eiderlike flight characteristics.
Weather overall was fair to poor; such
conditions were to be expected during this time of
the year. Our arrival on the island was delayed by
a day because of near-hurricane-force winds
(~70 mi/h [~110 km/h]), and winds were >30 mi/h
(>50 km/h) much of the time, decreasing to
≤20 mi/h (≤32 km/h) toward the end of our stay on
the island before increasing again; the average
wind speed was 19.8 mi/h (31.9 km/h; n =92
visual sampling sessions). In addition, frequent
precipitation (68 [73.9%] of 92 visual sessions)
resulted in difficult sampling conditions much of
the time.
VISUAL
Because the weather was so poor that use of
the radar was limited much of the time, we
emphasized visual sampling. All of the visual data
were collected during daylight hours, with
additional time spent every night attempting to
identify targets for the radar operators.
MOVEMENT RATES
Movements were dominated numerically (in
decreasing order) by alcids (almost entirely
murres), eiders, unidentified waterbirds, gulls
(especially Glaucous Gulls and Black-legged
Kittiwakes), other ducks (especially Long-tailed
Ducks), and cormorants; other groups, such as
loons, raptors, and shorebirds, occurred in
essentially trace amounts (Table 3). Surprisingly,
we recorded five flocks of Sabine’s Gulls, which
are very rare this far north at this time of the year
(Day et al. 2001); similarly, the records of
phalaropes are late for this latitude. For all taxa,
there was great among-day variation in mean
movement rates and in maximal movement rates
for one sampling session. For example, maximal
movement rates of total other ducks on single
sampling sessions ranged between 0 and
427.2 birds/h.
Eider movements consisted of all three of the
larger species (i.e., Spectacled, King, and Common
eiders); Steller’s Eider were not recorded (Table 3).
There was a suggestion that Common Eiders were
the most abundant of the three species and that
Spectacled Eiders were next in abundance;
however, most eiders flew so far offshore that the
number of eiders identifiable to species was low.
Maximal movement rates of total eiders on single
sampling sessions ranged between 14.4 birds/h and
1,814.4 birds/h.
Mean movement rates of total eiders varied
geographically, with all birds recorded flying only
over the ocean and none flying over the mountain,
the windfarm, or the town (Table 4). This absence
of overland movements by eiders flying also
suggests to us that the single eiderlike radar target
that was recorded flying over the windfarm was not
one of eiders (see "Radarmovement rates,"
below).
Almost all non-eider taxa were recorded
moving over the ocean, with raptors recorded
moving only over the windfarm and the town and
with only gulls recorded moving over all four
zones (Table 4). Gulls occurred predominantly
over the ocean, however.
Results
St. Lawrence Island Eiders 10Table 3.Movement rates (birds/h) of birds recorded visually near Gambell, Alaska, 23 October2 November 2002, by species/species-group and date; because so many taxa were seen, data are presented only for all eider species and for all species-groups. Data are presented as mean – SE, range, and n flocks (except for the Total across all dates, for which n is the number of days). Date Species/ 23 OC (n = 3) 24 OC (n = 2) 25 OC (n = 10) 26 OC (n = 10) species-group Mean – SE Range Mean – SE Range Mean – SE Range Mean – SE Range Total loons 0 – 0 00 0 – 0 00 0.7 – 0.5 04.8 0 – 0 00 Total cormorants 4.8 – 2.4 07.2 70.8 – 6.0 64.876.8 15.6 – 6.5 055.2 19.2 – 8.6 084.0 Spectacled Eider 0 – 0 00 0 – 0 00 0 – 0 00 0.7 – 0.5 04.8 King Eider 0 – 0 00 0 – 0 00 1.2 – 1.2 012.0 0 – 0 00 Common Eider 0 – 0 00 0 – 0 00 19.2 – 10.5 0105.6 0.5 – 0.5 04.8 Unidentified eider 870.4 – 230.8 420.01183.2 97.2 – 39.6 57.6136.8 228.0 – 158.8 4.81639.2 122.4 – 103.2 01046.4 Total eiders 870.4 – 230.8 420.01183.2 97.2 – 39.6 57.6136.8 284.8 – 168.1 4.81744.8 123.6 – 103.6 01051.2 Total other ducks 0 – 0 00 0 – 0 00 20.4 – 10.4 084.0 19.9 – 11.4 0100.8 Total raptors 0 – 0 00 0 – 0 00 0 – 0 00 0.5 – 0.3 02.4 Total shorebirds 0 – 0 00 0 – 0 00 0 – 0 00 7.4 – 5.2 048.0 Total gulls 0.8 – 0.8 02.4 42.0 – 10.8 31.252.8 53.5 – 17.4 0122.4 33.4 – 13.2 0115.2 Total alcids 0 – 0 00 0 – 0 00 181.7 – 103.7 01084.8 156.5 – 87.1 0825.6 Total waterbirds 0 – 0 00 42.0 – 10.8 0124.8 53.5 – 17.4 03360.0 37.4 – 20.0 0177.6 Total birds 876.0 – 229.4 427.21183.2 272.4 – 39.6 232.8312.0 1299.4 – 462.1 64.83708.0 397.9 – 141.2 01185.6
Results
11 St. Lawrence Island EidersTable 3. Continued. Date Species/ 27 OC (n = 10) 28 OC (n = 10) 29 OC (n 10) 30 OC (n = 10) species-group Mean – SE Range Mean – SE Range Mean – SE Range Mean – SE Range Total loons 0.2 – 0.2 02.4 0 – 0 00 1.4 – 0.7 07.2 0.5 – 0.3 02.4 Total cormorants 53.0 – 25.3 0256.8 3.6 – 2.4 024.0 0.7 – 0.7 07.2 10.3 – 4.5 040.8 Spectacled Eider 3.4 – 2.6 026.4 1.2 – 1.2 012.0 0.5 – 0.5 04.8 0.5 – 0.5 04.8 King Eider 0 – 0 00 0 – 0 00 0 – 0 00 1.2 – 1.2 012.0 Common Eider 0 – 0 00 0 – 0 00 0.7 – 0.7 07.2 1.9 – 1.7 016.8 Unidentified eider 31.4 – 11.4 0112.8 133.4 – 118.8 01200.0 26.2 – 10.7 0105.6 21.8 – 12.6 0132.0 Total eiders 34.8 – 11.6 0112.8 134.6 – 118.7 01200.0 27.4 – 10.9 0105.6 25.4 – 12.3 0132.0 Total other ducks 33.4 – 10.4 081.6 13.7 – 3.6 036.0 34.6 – 9.4 098.4 23.5 – 7.0 055.2 Total raptors 0.7 – 0.4 02.4 1.2 – 1.0 09.6 1.4 – 1.0 09.6 3.1 – 1.8 016.8 Total shorebirds 0 – 0 00 0 – 0 00 0 – 0 00 0 – 0 00 Total gulls 8.6 – 4.3 043.2 13.4 – 8.3 084.0 2.4 – 1.5 014.4 30.2 – 22.6 0232.8 Total alcids 6.0 – 5.0 050.4 17.0 – 6.9 064.8 1008.7 – 611.2 06156.0 5.0 – 1.7 014.4 Total waterbirds 75.8 – 53.6 0549.6 146.9 – 118.9 01207.2 0 – 0 00 0 – 0 00 Total birds 212.6 – 79.4 36.0828.0 330.5 – 156.9 9.61267.2 1,076.6 – 611.2 06208.8 99.1 – 43.3 0477.6
Results
St. Lawrence Island Eiders 12Table 3. Continued. Date Species/ 31 OC (n = 9) 1 NO (n = 10) 2 NO (n = 8) Total (n = 11) species-group Mean – SE Range Mean – SE Range Mean – SE Range Mean – SE Range Total loons 0.3 – 0.3 02.4 0.7 – 0.7 07.2 0.3 – 0.3 02.4 0.4 – 0.1 07.2 Total cormorants 14.1 – 3.7 036.0 14.9 – 5.5 048.0 73.5 – 27.2 0196.8 25.5 – 8.1 0256.8 Spectacled Eider 0 – 0 00 0 – 0 00 0 – 0 00 0.6 – 0.3 026.4 King Eider 0 – 0 00 1.4 – 1.0 07.2 0 – 0 00 0.3 – 0.2 012.0 Common Eider 0.8 – 0.8 07.2 0 – 0 00 0.6 – 0.6 04.8 2.2 – 1.7 0105.6 Unidentified eider 10.7 – 5.4 045.6 1.4 – 1.4 014.4 342.9 – 218.0 01814.4 171.4 – 76.8 01814.4 Total eiders 11.5 – 5.2 045.6 2.9 – 1.6 014.4 343.5 – 217.9 01814.4 174.5 – 76.7 01814.4 Total other ducks 0 – 0 00 1.0 – 1.0 09.6 144.6 – 55.5 0427.2 26.5. – 12.5 0427.2 Total raptors 5.1 – 3.7 033.6 0 – 0 00 0 – 0 00 1.1 – 0.5 033.6 Total shorebirds 0 – 0 00 0 – 0 00 0 – 0 00 0.7 – 0.7 048.0 Total gulls 145.3 – 35.8 0604.8 35.8 – 32.4 0326.4 619.8 – 402.2 03360.0 89.6 – 54.4 03360.0 Total alcids 0 – 0 00 0 – 0 00 1135.2 – 369.2 02059.2 228.2 – 127.6 06156.0 Total waterbirds 0.5 – 0.5 04.8 60.0 – 60.0 0600.0 526.2 – 331.4 02412.0 153.5 – 77.5 03360.0 Total birds 181.6 – 61.5 16.8645.6 115.2 – 69.9 0645.6 2483.1 – 1,038.4 117.68714.4 700.4 – 247.6 08714.4
Results
13 St. Lawrence Island EidersTable 4. Movement rates (birds/h) of birds recorded visually near Gambell, Alaska, 23 October2 November 2002, by species/species-group and movement zone; because so many taxa were seen, data are presented only for all eider species and for all species-groups. Data are presented as mean – SE; n = 92 sampling sessions for all samples. Movement zone Species/species-group Mountain Windfarm Town Ocean Total loons 0 – 0 0 – 0 0 – 0 0.4 – 0.1 Total cormorants 0 – 0 0 – 0 0 – 0 22.2 – 4.4 Spectacled Eider 0 – 0 0 – 0 0 – 0 0.7 – 0.3 King Eider 0 – 0 0 – 0 0 – 0 0.4 – 0.2 Common Eider 0 – 0 0 – 0 0 – 0 2.6 – 1.3 Unidentified eider 0 – 0 0 – 0 0 – 0 122.7 – 35.0 Total eiders 0 – 0 0 – 0 0 – 0 126.4 – 35.5 Total other ducks 0 – 0 0 – 0 0 – 0 28.5 – 6.5 Total raptors 0 – 0 0.2 – 0.1 1.1 – 0.4 0 – 0 Total shorebirds 0 – 0 0 – 0 0 – 0 0.8 – 0.6 Total gulls 0.7 – 0.7 5.6 – 1.9 2.9 – 1.2 79.2 – 38.1 Total alcids 0 – 0 0 – 0 0 – 0 248.2 – 83.5 Total waterbirds 0 – 0 0 – 0 0 – 0 166.6 – 55.3 Total birds 0.7 – 0.7 5.7 – 2.0 4.0 – 1.2 672.4 – 144.9
Results
St. Lawrence Island Eiders 14
FLOCK SIZE
Mean flock sizes varied dramatically among
species and species-groups (Table 5). The largest
mean flock sizes occurred in unidentified
waterbirds, followed (in decreasing order) by total
alcids, total eiders, total gulls, total shorebirds,
total other ducks, total cormorants, total raptors,
and total loons. Flocks of up to 1,000 gulls, 900
unidentified waterbirds, 720 alcids, and 550 eiders
were recorded.
FLIGHT ALTITUDE
Mean flight altitudes also varied dramatically
among species and species-groups (Table 5). The
highest mean flight altitude occurred in total gulls,
followed (in decreasing order) by total cormorants,
total raptors, unidentified waterbirds, total loons,
total other ducks, total eiders, and total alcids.
Eiders had a mean flight altitude of 1.8 m and a
maximal flight altitude of 15 m.
Because essentially all birds flew only over
the ocean, we were unable to examine whether
mean flight altitudes varied geographically (Table
6). One species, however, the Glaucous Gull,
occurred in all four zones, with a tendency for
decreasing mean flight altitudes from the
mountains to the ocean.
FLIGHT BEHAVIOR
Flight behavior was dominated overall by
contouring (i.e., following the shoreline; ~64% of
all flocks), followed by straight-line, directional
flight (~30% of all flocks); erratic behavior was
third in frequency, flying/landing was fourth in
frequency, and there was one case of circling flight
(Table 7). Loons, cormorants, eiders, other ducks,
phalaropes, alcids, and unidentified waterbirds all
exhibited high frequencies of contouring behavior,
whereas raptors and gulls exhibited substantial
frequencies of erratic flight.
Again, because essentially all birds flew over
the ocean, we were unable to examine whether
flight behavior varied geographically (Table 8). In
general, however, birds flying over the land tended
to exhibit lower frequencies of straight-line
behavior and higher frequencies of erratic behavior
than did birds flying over the ocean. To some
extent, this difference was driven by taxonomic
differences in behavior (i.e., loons, cormorants,
eiders, other ducks, alcids, and unidentified
waterbirds all exhibited high frequencies of
contouring flight, whereas gulls and raptors
exhibited more erratic flight), but some of the
difference also was driven by the fact that both the
gulls and the raptors were foraging over the land.
The gulls, in particular, foraged around the landfill
and over the shoreline, which resulted in
substantial erratic behavior.
RADAR
RADAR EFFICACY AND TARGET
IDENTIFICATION
During this study, the radar sampling was
more limited in coverage than the visual sampling
was. As indicated above, frequent heavy rain made
radar sampling impossible much of the time
because the electronic adjustments needed to
remove the rain-caused echoes from the display
screen also removed the bird-caused echoes from
the screen (Table 1). In addition, the proximity of
this sampling site to the ocean, in conjunction with
sea clutter caused by windy conditions and
associated high seas (up to 5 m high), affected the
accuracy of target detection and recognition.
Because the eiders were flying just off the
water’s surface, they were very difficult for the
radar to detect during periods of high winds and
high seas (i.e., the eiders were flying in the wave
troughs and, hence, often were missed by the radar;
Table 9). As a result, the radar detected only ~17%
of the flocks of eiders that were seen moving by the
sampling site, and eider targets were not recorded
on 11 (42.3%) of 26 sampling sessions when eiders
were recorded visually. In addition, a large
movement of cormorants during a period of
tailwinds on 31 October2 November resulted in
the misidentification of another 12 eiderlike
targets, plus the misidentification of a kittiwake as
an eider. (The 13 misidentified cormorant targets
were birds flying 4050 mi/h (6480 km/h) with
tailwinds or crosswinds of 1025 mi/h
(1640 km/h). The one unidentified kittiwake
target consisted of birds flying 50 mi/h (80 km/h)
with a 25-mi/h (40 km/h) tailwind.) Hence, the
misidentification rate may have been on the order
of 52% for targets that we otherwise would have
called "eiders." We suspect that part of the inflated
misidentification rate was caused by
species-specific differences in flight altitudes
Results
15 St. Lawrence Island Eiders
Table 5. Flock sizes and flight altitudes (m agl/asl) of birds recorded visually near Gambell, Alaska,
23 October2 November 2002, by species/species -group. Data are presented as mean – SE,
range, and n flocks.
Flock size Flight altitude (m)
Species/species-group Mean – SE Range n Mean – SE Range n
Pacific Loon 1.0 – 11 1 10.0 – 1010 1
Unidentified loon 1.5 – 0.2 13 11 3.5 – 1.7 120 11
Total loons 1.4 – 0.2 13 12 4.0 – 1.6 120 12
Unidentified cormorant 6.0 – 0.8 165 22.1 – 2.1 1100 141
Total cormorants 6.0 – 0.8 165 142 22.1 – 2.1 1100 141
Spectacled Eider 2.9 – 1.1 111 9 2.1 – 0.6 15 9
King Eider 4.0 – 0.3 35 4 1.3 – 0.3 12 4
Common Eider 5.8 – 1.6 128 17 1.4 – 0.1 13 17
Unidentified eider 32.9 – 7.9 1550 143 1.9 – 0.1 115 143
Total eiders 28.0 – 6.5 1550 173 1.8 – 0.1 115 173
White-winged Scoter 10.8 – 5.1 230 5 2.4 – 0.7 15 5
Unidentified scoter 36.0 – 3636 1 2.0 – 22 1
Long-tailed Duck 9.0 – 11.4 185 108 1.9 – 0.1 110 108
Unidentified duck 30.0 – 3030 1 1.0 – 11 1
Total other ducks 9.5 – 1.1 185 115 1.9 – 0.1 110 115
Gyrfalcon 1.0 – 0 11 3 12.0 – 4.2 620 3
Common Raven 2.8 – 0.6 17 16 20.2 – 12.1 2200 16
Total raptors 2.5 – 0.5 17 19 18.9 – 10.1 2200 19
Unidentified phalarope 15.5 – 4.5 1120 2 1.0 – 0 11 2
Total shorebirds 15.5 – 4.5 1120 2 1.0 – 0 11 2
Glaucous Gull 13.0 – 2.6 1200 107 52.1 – 4.9 1200 99
Black-legged Kittiwake 26.8 – 7.3 1200 36 6.4 – 1.3 130 36
Sabine’s Gull 3.4 – 0.2 112 5 10.6 – 4.2 325 5
Unidentified gull 202.8 – 199.3 31,000 5 28.0 – 2.0 2030 5
Total gulls 22.1 – 6.9 11,000 153 38.5 – 3.8 1200 145
Common Murre 3.0 – 0.9 15 4 1.3 – 0.3 12 4
Unidentified murre 56.5 – 7.0 1720 168 1.3 – 0.1 15 168
Pigeon Guillemot 1.0 – 0 11 3 1.3 – 0.3 12 3
Unidentified guillemot 1.0 – 11 1 1.0 – 11 1
Total alcids 54.1 – 6.8 1720 176 1.3 – 0 15 176
Unidentified waterbird 76.0 – 13.8 1900 84 5.2 – 1.6 1100 84
Total waterbirds 76.0 – 13.8 1900 84 5.2 – 1.6 1100 84
Total 29.8 – 2.7 11000 876 11.9 – 0.9 1200 867
Results
St. Lawrence Island Eiders 16Table 6. Flight altitudes (m agl/asl) of birds recorded visually near Gambell, Alaska, 23 October2 November 2002, by species/species-group and movement zone. Data are presented as mean – SE and n flocks. Movement zone Mountain Windfarm Town Ocean Species/species-group Mean – SE n Mean – SE n Mean – SE n Mean – SE n Pacific Loon – 0 – 0 – 0 10.0 – 1 Unidentified loon – 0 – 0 – 0 3.5 – 1.7 11 Total loons – 0 – 0 – 0 4.0 – 1.6 12 Unidentified cormorant – 0 – 0 – 0 22.1 – 2.1 141 Total cormorants – 0 – 0 – 0 22.1 – 2.1 141 Spectacled Eider – 0 – 0 – 0 2.1 – 0.6 9 King Eider – 0 – 0 – 0 1.3 – 0.3 4 Common Eider – 0 – 0 – 0 1.4 – 0.1 17 Unidentified eider – 0 – 0 – 0 1.9 – 0.2 143 Total eiders – 0 – 0 – 0 1.8 – 0.1 173 White-winged Scoter – 0 – 0 – 0 2.4 – 0.7 5 Unidentified scoter – 0 – 0 – 0 2.0 – 1 Long-tailed Duck – 0 – 0 – 0 1.9 – 0.1 108 Unidentified duck – 0 – 0 – 0 1.0 – 1 Total other ducks – 0 – 0 – 0 1.9 – 0.1 115 Gyrfalcon – 0 – 0 12.0 – 4.2 3 – 0 Common Raven – 0 107.5 – 92.5 2 7.7 – 1.3 14 – 0 Total raptors – 0 107.5 – 92.5 2 8.5 – 1.3 17 – 0 Unidentified phalarope – 0 – 0 – 0 1.0 – 0 2 Total shorebirds – 0 – 0 – 0 1.0 – 0 02
Results
17 St. Lawrence Island EidersTable 6. Continued. Movement zone Mountain Windfarm Town Ocean Species/species-group Mean – SE n Mean – SE n Mean – SE n Mean – SE n Glaucous Gull 70.0 – 1 67.1 – 10.6 28 47.0 – 10.1 16 45.4 – 6.4 54 Black-legged Kittiwake – 0 – 0 – 0 6.4 – 1.3 36 Sabine’s Gull – 0 – 0 – 0 10.6 – 4.2 5 Unidentified gull – 0 – 0 – 0 28.0 – 2..0 5 Total gulls 70.0 – 1 67.1 – 10.6 28 47.0 – 10.1 16 28.7 – 4.0 100 Common Murre – 0 – 0 – 0 1.3 – 0.3 4 Unidentified murre – 0 – 0 – 0 1.3 – 0.1 168 Pigeon Guillemot – 0 – 0 – 0 1.6 – 0.2 3 Unidentified guillemot – 0 – 0 – 0 1.0 – 1 Total alcids – 0 – 0 – 0 1.3 – 0.1 176 Unidentified waterbird – 0 – 0 – 0 5.2 – 1.6 84 Total waterbirds – 0 – 0 – 0 5.2 – 1.6 84
Results
St. Lawrence Island Eiders 18
Table 7. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group. Data are presented as number (percentage) in each category
and n flocks.
Behavior
Species/species-group Straight-line Erratic Circling Flying/landing Contouring n
Pacific Loon 0 (00) 0 (0) 0 (0) 0 (0) 1 (100.0) 1
Unidentified loon 2 (18.2) 0 (0) 0 (0) 0 (0) 9 (81.8) 11
Total loons 2 (16.7) 0 (0) 0 (0) 0 (0) 10 (83.3) 12
Unidentified cormorant 26 (18.3) 0 (0) 0 (0) 2 (1.4) 114 (80.3) 142
Total cormorants 26 (18.3) 0 (0) 0 (0) 2 (1.4) 114 (80.3) 142
Spectacled Eider 1 (11.1) 0 (0) 0 (0) 1 (11.1) 7 (77.8) 9
King Eider 0 (0) 0 (0) 0 (0) 0 (0) 4 (100.0) 4
Common Eider 3 (17.6) 0 (0) 0 (0) 1 (5.9) 13 (76.5) 17
Unidentified eider 42 (29.4) 1 (0.7) 0 (0) 7 (4.9) 93 (65.0) 143
Total eiders 46 (26.6) 1 (0.6) 0 (0) 9 (5.2) 117 (67.6) 173
White-winged Scoter 1 (20.0) 0 (0) 0 (0) 0 (0) 4 (80.0) 5
Unidentified scoter 0 (0) 0 (0) 0 (0) 1 (100.0) 0 (0) 1
Long-tailed Duck 15 (13.9) 0 (0) 0 (0) 2 (1.9) 91 (84.3) 108
Unidentified duck 1 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 1
Total other ducks 17 (14.8) 0 (0) 0 (0) 3 (2.6) 95 (82.6) 115
Gyrfalcon 0 (0) 3 (100.0) 0 (0) 0 (0) 0 (0) 3
Common Raven 6 (37.5) 10 (62.5) 0 (0) 0 (0) 0 (0) 16
Total raptors 6 (31.6) 13 (68.4) 0 (0) 0 (0) 0 (0) 19
Unidentified phalarope 0 (0) 0 (0) 0 (0) 1 (50.0) 1 (50.0) 2
Total shorebirds 0 (0) 0 (0) 0 (0) 1 (50.0) 1 (50.0) 2
Glaucous Gull 81 (75.7) 15 (14.0) 1 (0.9) 0 (0) 10 (9.3) 107
Black-legged Kittiwake 12 (33.3) 3 (8.3) 0 (0) 1 (2.8) 20 (55.5) 36
Sabine’s Gull 2 (40.0) 1 (20.0) 0 (0) 0 (0) 2 (40.0) 5
Unidentified gull 5 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 5
Total gulls 100 (65.4) 19 (12.4) 1 (0.7) 1 (0.7) 32 (20.9) 153
Common Murre 2 (50.0) 0 (0) 0 (0) 0 (0) 2 (50.0) 4
Unidentified murre 20 (11.9) 0 (0) 0 (0) 3 (1.8) 145 (86.3) 168
Pigeon Guillemot 0 (0) 0 (0) 0 (0) 1 (33.3) 2 (66.7) 3
Unidentified guillemot 1 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 1
Total alcids 23 (13.1) 0 (0) 0 (0) 4 (2.3) 149 (84.7) 176
Unidentified waterbird 45 (53.6) 1 (1.2) 0 (0) 0 (0) 38 (45.2) 84
Total waterbirds 45 (53.6) 1 (1.2) 0 (0) 0 (0) 38 (45.2) 84
Total 265 (30.3) 34 (3.9) 1 (0.1) 20 (2.3) 556 (63.5) 876
Results
19 St. Lawrence Island Eiders
Table 8. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group and movement zone. Data are presented as number
(percentage) in each category and n flocks.
Mountain
Species/species-group
Straight-
line
Erratic
Circling
Flying/
landing
Contouring
n
Pacific Loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total loons 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified cormorant 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total cormorants 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Spectacled Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
King Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total eiders 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
White-winged Scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Long-tailed Duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total other ducks 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Gyrfalcon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Raven 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total raptors 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified phalarope 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total shorebirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Glaucous Gull 0 (0) 0 (0) 1 (100.0) 0 (0) 0 (0) 1
Black-legged Kittiwake 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Sabine’s Gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total gulls 0 (0) 0 (0) 1 (100.0) 0 (0) 0 (0) 1
Common Murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Pigeon Guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total alcids 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified waterbird 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total waterbirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total 0 (0) 0 (0) 1 (100.0) 0 (0) 0 (0) 1
Results
St. Lawrence Island Eiders 20
Table 8. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group and movement zone (continued).
Windfarm
Species/species-group
Straight-
line
Erratic
Circling
Flying/
landing
Contouring
n
Pacific Loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total loons 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified cormorant 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total cormorants 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Spectacled Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
King Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total eiders 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
White-winged Scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Long-tailed Duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total other ducks 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Gyrfalcon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Raven 1 (50.0) 1 (50.0) 0 (0) 0 (0) 0 (0) 2
Total raptors 1 (50.0) 1 (50.0) 0 (0) 0 (0) 0 (0) 2
Unidentified phalarope 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total shorebirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Glaucous Gull 26 (86.7) 4 (13.3) 0 (0) 0 (0) 0 (0) 30
Black-legged Kittiwake 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Sabine’s Gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total gulls 26 (86.7) 4 (13.3) 0 (0) 0 (0) 0 (0) 30
Common Murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Pigeon Guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total alcids 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified waterbird 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total waterbirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total 27 (84.4) 5 (15.6) 0 (0) 0 (0) 0 (0) 32
Results
21 St. Lawrence Island Eiders
Table 8. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group and movement zone (continued).
Town
Species/species-group
Straight-
line
Erratic
Circling
Flying/
landing
Contouring
n
Pacific Loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified loon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total loons 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified cormorant 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total cormorants 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Spectacled Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
King Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified eider 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total eiders 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
White-winged Scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified scoter 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Long-tailed Duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified duck 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total other ducks 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Gyrfalcon 0 (0) 3 (100.0) 0 (0) 0 (0) 0 (0) 3
Common Raven 5 (35.7) 9 (64.3) 0 (0) 0 (0) 0 (0) 14
Total raptors 5 (29.4) 12 (70.6) 0 (0) 0 (0) 0 (0) 17
Unidentified phalarope 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total shorebirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Glaucous Gull 14 (77.8) 4 (22.2) 0 (0) 0 (0) 0 (0) 18
Black-legged Kittiwake 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Sabine’s Gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified gull 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total gulls 14 (77.8) 4 (22.2) 0 (0) 0 (0) 0 (0) 18
Common Murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified murre 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Pigeon Guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified guillemot 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total alcids 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified waterbird 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total waterbirds 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total 19 (54.3) 16 (45.7) 0 (0) 0 (0) 0 (0) 35
Results
St. Lawrence Island Eiders 22
Table 8. Flight behavior of birds recorded visually near Gambell, Alaska, 23 October2 November
2002, by species/species-group and movement zone (continued).
Ocean
Species/species-group
Straight-line
Erratic
Circling
Flying/
landing
Contouring
n
Pacific Loon 0 (0) 0 (0) 0 (0) 0 (0) 1 (100.0) 1
Unidentified loon 2 (18.2) 0 (0) 0 (0) 0 (0) 9 (81.8) 11
Total loons 2 (16.7) 0 (0) 0 (0) 0 (0) 10 (83.3) 12
Unidentified cormorant 26 (18.3) 0 (0) 0 (0) 2 (1.4) 114 (80.3) 142
Total cormorants 26 (18.3) 0 (0) 0 (0) 2 (1.4) 114 (80.3) 142
Spectacled Eider 1 (11.1) 0 (0) 0 (0) 1 (11.1) 7 (77.8) 9
King Eider 0 (00) 0 (0) 0 (0) 0 (0) 4 (100.0) 4
Common Eider 3 (17.6) 0 (0) 0 (0) 1 (5.9) 13 (76.5) 17
Unidentified eider 42 (29.4) 1 (0.7) 0 (0) 7 (4.9) 93 (65.0) 143
Total eiders 46 (26.6) 1 (0.6) 0 (0) 9 (5.2) 117 (67.6) 173
White-winged Scoter 1 (20.0) 0 (0) 0 (0) 0 (0) 4 (80.0) 5
Unidentified scoter 0 (0) 0 (0) 0 (0) 1 (100.0) 0 (0) 1
Long-tailed Duck 15 (13.9) 0 (0) 0 (0) 2 (1.9) 91 (84.3) 108
Unidentified duck 1 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 1
Total other ducks 17 (14.8) 0 (0) 0 (0) 3 (2.6) 95 (82.6) 115
Gyrfalcon 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Common Raven 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Total raptors 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0
Unidentified phalarope 0 (0) 0 (0) 0 (0) 1 (50.0) 1 (50.0) 2
Total shorebirds 0 (0) 0 (0) 0 (0) 1 (50.0) 1 (50.0) 2
Glaucous Gull 41 (70.7) 7 (12.1) 0 (0) 0 (0) 10 (17.2) 58
Black-legged Kittiwake 12 (33.3) 3 (8.3) 0 (0) 1 (2.8) 20 (55.5) 36
Sabine’s Gull 2 (40.0) 1 (20.0) 0 (0) 0 (0) 2 (40.0) 5
Unidentified gull 5 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 5
Total gulls 60 (57.7) 11 (10.6) 0 (0) 1 (1.0) 32 (30.8) 104
Common Murre 2 (50.0) 0 (0) 0 (0) 0 (0) 2 (50.0) 4
Unidentified murre 20 (11.9) 0 (0) 0 (0) 3 (1.8) 145 (86.3) 168
Pigeon Guillemot 0 (0) 0 (0) 0 (0) 1 (33.3) 2 (66.7) 3
Unidentified guillemot 1 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 1
Total alcids 23 (13.1) 0 (0) 0 (0) 4 (2.3) 149 (84.7) 176
Unidentified waterbird 45 (53.6) 1 (1.2) 0 (0) 0 (0) 38 (45.2) 84
Total waterbirds 45 (53.6) 1 (1.2) 0 (0) 0 (0) 38 (45.2) 84
Total 219 (27.1) 13 (1.7) 0 (0) 20 (2.5) 556 (68.8) 808
Results
23 St. Lawrence Island Eiders
Table 9. Efficiency of detection of eider radar targets near Gambell, Alaska, 23 October3 November
2002, by sampling session. Data are presented as n eiderlike targets, n visual flocks of eiders
recorded visually, and n eiders recorded visually during concurrent sampling.
Sampling
session
Number of eiderlike
radar targets
Number of flocks of eiders
seen visually Number of eiders seen visually
298.01 1 2a 72
298.02 2 3a 98
298.03 1 8a 727
298.04 0 3 13
298.05 0 5a 26
298.07 0 2 9
298.08 0 5a 61
298.09 1 4 10
298.10 0 1 2
304.05 0 1 19
304.06 0 1 3
304.08 0 1 3
304.09 0 2 11
304.10 3 (but 3 are cormorants) 2 7
304.11 3 (but 2 are cormorants) 0 0
304.12 3 (but 2 are cormorants) 0 0
305.01 5 (but 3 are cormorants) 0 0
305.02 2 (but 1 is cormorant) 2 6
305.03 2 1 3
305.05 1 1 3
305.10 1 0 0
306.06 1 (but kittiwake) 3 205
306.07 0 8 82
306.08 1 (but cormorant) 5 41
306.09 0 4 756
306.10 0 7 61
Total 12 (plus 13
misidentified)
69 2,224
a Because so many eiders were moving by in long strings, multiple flocks sometimes were counted as one on this first
day of sampling because the emphasis was on an accurate count of birds, rather than on flocks; hence, the number of
flocks probably is underestimated.
Results
St. Lawrence Island Eiders 24
(Table 5), in that targets of cormorants flying with
a tailwind looked much like those of eiders on the
radar screen, but the eiders were flying so low and
the cormorants were flying so high that the number
of misidentified eiders was inflated because of a
higher probability of detecting cormorants.
Although it is clear that the number of eider
flocks and eiders recorded by the radar over the
ocean was underestimated, the radar did an
excellent job of detecting targets over land, which
was an important aspect of this study. The view
over land was excellent and was not affected by sea
clutter. Hence, we believe that we missed no
targets flying over land, especially targets of eiders.
Therefore, we considered the radar to provide an
underestimate of numbers of eiders moving over
the ocean but to provide an accurate estimate of
numbers of eiders moving over land.
MOVEMENT RATES
"Eiders" exhibited low mean movement rates
during most dates and under most weather
conditions, with most means averaging
13 targets/h (Table 10). The maximal movement
rate for one sampling session was 9.6 targets/h,
recorded on 31 October. Mean movement rates
were ~175% higher at night than during the day,
200% higher during periods of no precipitation
than during precipitation, and 50% higher during
crosswinds than during tailwinds.
"Non-eiders" exhibited mean movement rates
that were ~20 times those for "eiders," with most
means averaging ~25 targets/h (Table 10); there
was substantial among-day variation in movement
rates. The maximal movement rate for one
sampling session was 196.8 targets/h, recorded on
2 November. Mean movement rates were ~160%
higher during the day than at night (primarily
because of all of the daytime gull movements),
~72% higher during periods of no precipitation
than during precipitation, and ~20% higher during
tailwinds than during crosswinds.
Mean movement rates of "eiders" varied
geographically, with essentially all birds flying
only over the ocean and none flying over the
mountain and town (Table 11). We did, however,
record one unidentified target over the proposed
windfarm that we classified as an "eider" on 25
October. This target occurred during the day,
during a period of no precipitation, and during
tailwinds (Table 11). We suspect that this target
was not one of eiders and instead suspect that it
was gulls flying with a tailwind; however, we were
unable to locate it visually as it passed over the
windfarm to confirm this suspicion. Mean rates
were <0.1 targets/h over the windfarm, 0 targets/h
over the mountain and town, and ~1.5 targets/h
over the ocean.
Mean movement rates of "non-eiders" also
varied geographically, with none recorded over the
mountain, moderate numbers moving over the
proposed windfarm and town, and much higher
numbers moving over the ocean (Table 11). Mean
rates were ~2 targets/h over the windfarm,
~4 targets/h over town, and ~20 targets/h over the
ocean.
FLIGHT BEHAVIOR
"Eiders" were recorded exhibiting three of the
five standardized behaviors (Table 12). Overall,
~90% of all "eider" targets flew with straight-line,
directional characteristics. Another ~7% of all
"eider" targets flew by contouring (i.e., following
the coastline); low percentages of "eider" targets
flew erratically. Frequencies of erratic flight
behavior, which could be associated with a higher
probability of hitting structures, were so low
overall that no pattern by factor could be discerned.
"Non-eiders" were recorded exhibiting all five
of the standardized behaviors (Table 12). Overall,
~60% of all "non-eider" targets flew with
straight-line characteristics. Another ~34% flew
by contouring; this behavior was seen most
frequently in foraging gulls, which frequently
followed the shoreline. The remaining three
behaviors occurred infrequently, with erratic
behavior being the most common of the three.
The one "eider" target recorded over the
proposed windfarm flew with straight-line
characteristics (Table 13). Otherwise, all other
targets were recorded over the ocean, flying
primarily with straight-line behavior.
Most of the "non-eider" targets passing over
the proposed windfarm flew with straight-line
characteristics, with the remaining targets flying
erratically, by circling, or flying/landing (Table
13). Over town, most "non-eider" targets flew with
straight-line characteristics, with the remaining
birds flying erratically or contouring along the
shoreline north of town. Over the ocean, most
Results
25 St. Lawrence Island Eiders
Table 10. Movement rates (targets/h) of birds recorded migrating on radar near Gambell, Alaska, 23
October2 November 2002, by species-group and factor. Data are presented as mean – SE
radar targets/h, range, and n sampling sessions (except for the Total across all dates, for which
n is the number of days).
Species-group Factor Attribute Mean – SE Range n
"Eiders" Date 25 OC 1.0 – 0.5 04.8 10
26 OC 0 – 00 1
31 OC 3.4 – 0.9 09.6 17
1 NO 1.1 – 0.4 04.8 16
2 NO 0.9 – 0.4 04.8 16
Total 1.3 – 0.4 09.6 5
Time of day Day 1.2 – 0.3 07.2 47
Night 3.3 – 1.1 09.6 13
Total 1.6 – 0.3 09.6 60
Precipitation level No precipitation 2.4 – 0.6 09.6 31
Precipitation 0.8 – 0.3 06.0 29
Total 1.6 – 0.3 09.6 60
Wind type Crosswind 2.4 – 1.0 09.6 11
Tailwind 1.6 – 0.4 09.6 49
Total 1.6 – 0.3 09.6 60
"Non-eiders" Date 25 OC 40.1 – 8.0 9.688.8 10
26 OC 24.0 – 24.0 1
31 OC 19.2 – 2.5 4.838.4 17
1 NO 16.1 – 4.6 2.469.6 16
2 NO 36.2 – 12.8 0196.8 16
Total 27.1 – 4.7 0196.8 5
Time of day Day 30.5 – 5.0 0196.8 47
Night 11.8 – 2.5 026.4 13
Total 26.4 – 4.1 0196.8 60
Precipitation level No precipitation 33.1 – 6.6 4.8196.8 31
Precipitation 19.3 – 4.3 0112.8 29
Total 26.4 – 4.1 0196.8 60
Wind type Crosswind 22.7 – 2.9 7.238.4 11
Tailwind 27.3 – 4.9 0196.8 49
Total 26.4 – 4.1 0196.8 60
Results
St. Lawrence Island Eiders 26Table 11. Movement rates (targets/h) of birds recorded on radar near Gambell, Alaska, 23 October2 November 2002, by species-group, factor, and movement zone. Data are presented as mean – SE (range) radar targets/h by movement zone; for all samples, n for all is 60 sampling sessions. Movement zone Species-group Mountain Windfarm Town Ocean "Eiders" 0 – 0 (00) <0.1 – <0.1 (02.4) 0 – 0 (00) 1.6 – 0.3 (09.6) Non-eiders" 0 – 0 (00) 2.2 – 0.6 (024.0) 4.0 – 0.8 (033.6) 20.2 – 3.9 (0196.8) Table 12. Flight behavior of birds recorded on radar near Gambell, Alaska, 23 October2 November 2002, by species-group. Data are presented as number (percentage) in each category and n flocks. Flight behavior Species-group Factor Attribute Straight-line Erratic Circling Flying/ landing Contouring n "Eiders" Time of day Day 20 (83.3) 1 (4.2) 0 (0) 0 (0) 2 (8.3) 23 Night 17 (94.4) 0 (0) 0 (0) 0 (0) 1 (5.6) 18 Precipitation level No precipitation 30 (96.8) 1 (3.2) 0 (0) 0 (0) 0 (0) 31 Precipitation 7 (63.6) 0 (0) 0 (0) 0 (0) 3 (27.3) 10 Wind type Crosswind 11 (100.0) 0 (0) 0 (0) 0 (0) 0 (0) 11 Tailwind 26 (83.9) 1 (3.2) 0 (0) 0 (0) 3 (9.7) 30 Total Total 37 (90.2) 1 (2.4) 0 (0) 0 (0) 3 (7.3) 41 "Non-eiders" Time of day Day 342 (58.8) 29 (5.0) 2 (0.3) 3 (0.5) 206 (35.4) 582 Night 42 (65.5) 7 (10.9) 1 (1.6) 0 (0) 14 (21.9) 64 Precipitation level No precipitation 276 (65.9) 28 (6.7) 2 (0.5) 0 (0) 113 (27.0) 419 Precipitation 108 (47.1) 8 (3.5) 1 (0.4) 3 (1.3) 107 (47.1) 227 Wind type Crosswind 91 (87.5) 13 (12.5) 0 (0) 0 (0) 0 (0) 104 Tailwind 293 (54.1) 23 (4.3) 3 (0.6) 3 (0.6) 220 (40.6) 542 Total Total 384 (59.4) 36 (5.6) 3 (0.5) 3 (0.5) 220 (34.1) 646
Results
27 St. Lawrence Island EidersTable 13. Flight behavior of birds recorded on radar near Gambell, Alaska, 23 October2 November 2002, by species-group and movement zone. Data are presented as number (percentage) in each category and n flocks. Movement zone Mountain Windfarm Species-group Straight-line Erratic Circling Flying/ landing Contouring n Straight-line Erratic Circling Flying/ landing Contouring n "Eiders" 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 1 (50.0) 0 (0) 0 (0) 0 (0) 0 (0) 1 "Non-eiders" 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 46 (93.9) 1 (2.0) 1 (2.0) 1 (2.0) 0 (0) 49 Movement zone Town Ocean Species-group Straight-line Erratic Circling Flying/ landing Contouring n Straight-line Erratic Circling Flying/ landing Contouring n "Eiders" 0 (0) 0 (0) 0 (0) 0 (0) 0 (0) 0 36 (90.0) 1 (2.5) 0 (0) 0 (0) 3 (7.5) 40 "Non-eiders" 75 (75.8) 14 (14.1) 0 (0) 0 (0) 10 (10.1) 99 263 (52.8) 21 (4.2) 2 (0.4) 2 (0.4) 210 (42.2) 498
Discussion
St. Lawrence Island Eiders 28
"non-eider" targets flew with straight-line
characteristics or by contouring, with the other
three behaviors occurring sparingly.
AVIAN MORTALITY
We recorded no birds of any species dead at
the FAA towers and the meteorological tower
(Table 2). No dead birds were found in spite of the
presence of dense fog on some days.
DISCUSSION
These data suggest several important insights
about the movements of birds in the vicinity of the
proposed windfarm at Gambell. First, the number
of birds moving and wintering in this area is large,
with birds constantly in motion: we saw a total of
>26,000 birds during our sampling, for an overall
mean daily movement rate of 700 birds/h.
Although Fay (1961) suggested that waterfowl
were scarce at St Lawrence in the fall
(Septemberlate November), we saw large
numbers of ducks (4,845 eiders and 1,092 other
ducks). We also saw 9,513 alcids, essentially all of
which were murres, and another 6,388 waterbirds
(ducks or murres), indicating that a diversity of
bird species occurs in number near Gambell in the
fall.
Eiders form a significant proportion of the
birds seen near Gambell at this time of the year,
representing 4,845 (24.5%) of the 19,784 identified
birds; if all of the unidentified waterbirds actually
were eiders, up to 42.9% of the birds seen would
have been eiders. Hence, eiders represented
2443% of the birds occurring at Gambell during
this period. Although sample sizes were small,
Common Eiders appeared to be the most abundant
eider species, with Spectacled Eiders second in
abundance and King Eiders third in abundance.
Spectacled Eiders winter in the polynyas off of the
southern side of St. Lawrence Island and in the
zone of labile ice southwest of St. Lawrence Island,
passing Gambell in substantial numbers (Petersen
et al. 1995, 1999, 2000).
The movement-rate data indicate that most
birds pass by Gambell over the ocean, with very
little movement of any species over the proposed
windfarm (primarily gulls and raptors). This
pattern also was true at night, as indicated by the
radar data, and was especially true at all times for
eiders on radar: we recorded only one eiderlike
target on radar flying over the proposed windfarm,
and we suspect that it was not of an eider. We also
saw no eiders (and few birds of only a few species)
flying over land during extensive visual surveys.
Although we saw no eiders or waterfowl of
any species flying over land, local villagers
informed us that eiders and Long-tailed Ducks fly
over the spit on which Gambell occurs after the sea
freezes and snow obscures the boundary between
sea and land. At those times, these birds "cut the
corner" over the spit while moving back and forth
as polynyas open and close on the northern and
southern sides of the island. Local villagers told us
that, when these birds do cross the spit, they
occasionally hit the wires at the FAA towers.
Hence, the absence of dead birds that we recorded
at the FAA towers probably reflects the fact that
birds were not yet flying over land because the sea
had not yet frozen.
The flight-altitude data indicate that flight
altitudes of most species over the ocean (with the
exception of cormorants and gulls) were so low
that, unless they changed altitude as they crossed
land, they would pass under the rotor blades of the
turbines, given the dimensions that are envisioned
at this time. The towers will be 24, 30, or 40 m
high, and the rotors will be either 15 or 20 m in
diameter (i.e., having 7.510 m blade lengths),
resulting in sweep areas for the three tower designs
of 1434 m high, 2040 m high, and 3050 m
high, respectively. On the other hand, it is likely
that many gulls, cormorants, and raptors will fly at
altitudes that put them at risk of collisions. It is
unclear whether eiders will increase in height as
they cross the spit later in the winter; at Pt. Barrow,
birds do increase in altitude as they cross the base
of Barrow Spit, but that increase appears to be
related much more to the presence of numerous
hunters than it does to an aversion to flying over
land (Day and Rose, pers. obs.). At Northstar
Island, the mean flight altitude of eiders flying over
the ocean was 7.9 m (Day et al. 2002), or slightly
higher than what we recorded here.
The behavioral data indicate that most of the
birds seen in this study flew by contouring (i.e.,
following the shoreline); by flying over the ocean
or the shoreline, those birds will have little chance
of hitting the turbines. On the other hand, if a flock
does deviate to cross over the spit, the other
Conclusions and Recommendations
29 St. Lawrence Island Eiders
members of the flock will follow, resulting in a low
probability of collision but a high probability of
substantial mortality if a collision does occur.
Erratic behavior is one that we believe results in a
higher risk of collision, because the birds are
moving around the northern part of the spit in
numerous directions. Foraging gulls and ravens
both seem to exhibit frequent erratic behavior,
suggesting that they have a higher probability of
collision with turbines than the eiders do. On the
other hand, their slow flight speeds, which gives
them a fair degree of maneuverability, may help to
some extent to counteract the higher probability of
collision caused by straight-line flight behavior.
Of nine windpower sites for which mortality data
were summarized (Erickson et al. 2001), gulls were
recorded being killed at three of them and ravens
were recorded being killed at four of them (and
several of the other sites occurred in locations
outside of the range of ravens). The mortality of
gulls and ravens represented up to 4.8% and 5.4%,
respectively, of all birds killed at windpower sites,
suggesting that their slow flight speeds do not
prevent their mortality.
Finally, the visual and radar data indicate that,
at this site, the utility of radar was limited because
of two factors: heavy precipitation and high seas.
Rain limited the use of this X-band radar a
substantial percentage of the time; given the fact
that Gambell receives precipitation (Alaska
Community Database; see website in "Study
Area," above) ~83% of the days/year, this
limitation should not be unexpected. High seas
caused problems in detection because the eiders
flew between wave troughs during periods of high
seas, so that the radar often could not detect them
below the wave-tops. The problems noted here are
important, in that they indicate that radar will be
limited as a sampling tool in some circumstances
(e.g., some locations, some seasons) in coastal
communities of western Alaska, particularly if
wind turbines are constructed on the coast itself.
On the other hand, the ability of the radar to sample
a much larger area than the visual observers can
sample, the fact that over -land observations near
proposed turbines are important and that the radar
sampled those areas well, and the fact that the radar
can sample during periods of limited visibility (the
radar indicated that nocturnal movement rates of
all birds were substantial) compensate for its
limitations in most cases.
CONCLUSIONS AND
RECOMMENDATIONS
Although it is difficult to evaluate with
certainty the probability of mortality of eiders,
especially Spectacled Eiders, and other seabirds at
the proposed windfarm at Gambell, we believe that
the probability of fall mortality of eiders while the
sea is unfrozen is extremely low. On the other
hand, local residents indicated that, once the ocean
freezes and the exact boundary of the shoreline is
obscured, eiders and other ducks moving back and
forth past the island occasionally cross over the
spit, sometimes hitting the FFA towers or their guy
wires. It is unclear what the frequency of this
overland flight is during those conditions and,
hence, what the actual collision probability will be.
We believe, however, that locating the windfarm
toward the base of Sevuokuk Mountain (i.e., in the
vicinity of the proposed location) will decrease the
probability of collision for ducks crossing the spit
considerably from that if the windfarm is located
toward the tip of the spit. Finally, although
summer bird movements were not studied, there
are large auklet colonies on nearby Sevuokuk
Mountain . We suggest that the location of the
auklet colony be a consideration in site selection at
this windfarm.
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