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HomeMy WebLinkAboutAPA2254o o D- O O· r 1 U II II lJ [j o Ll IJ. Q ,1 o o O· [}{]&OO~&c @:OO&®©@ Susitna Joint Venture Document Number d-~S±' Please Return To DOCUMENTCONTROL Chapter 12 173 "true"Dall's sheep rO.d.daZZO,also com- monly referred to as the Alaskan Dall's sheep.It is found in Alaska,the Yukon and Northwest Territories,and the extreme northwestern part of British Columbia.The other is Stone's sheep (O.d.stoneiJ of northern British Columbia and the southern part of the Yukon Territory.Both subspecies were named after persons,W.H.Dall and A.J.Stone,respectively.Consequently,their common names should be capitalized and used in possessive forms rather than the frequently used but incorrect forms "Dall sheep"and "Stone sheep."To avoid confu- sion,further reference in this chapter to Dall's sheep will indicate the subspecies by that name and differentiate it from Stone's sheep.Readers should keep in mind,how- ever,that both Dall's sheep and Stone's sheep subspecies are of the Dall's sheep species. Two other subspecies formerly were recognized,the white sheep ro.d.ke- naiensis)of the Kenai Peninsula,Alaska (Buechner 1960a),and the gray or saddle- back Fannin's sheep rO.d.fannini)found between the main ranges of Dall's and Stone's sheep.The former now is considered identical to other Dall's sheep,and the latter is recognized as no more than a color grada- tion between the white Dall's and dark Stone's sheep. Lyman Nichols,Jr. Wildlife Biologist Alaska l)epartment ofFish and Game Cooper Landing,Alaska DALL'S SHEEP #~'2.S4 There is some debate among taxonomists ether American thinhorn sheep actually separate species or,in fact,are species of Siberian snow sheep,which very similar in size and appearance to ne's sheep CCherniavski 1962,Cowan 0,Rausch 1961).Arguments tend to or the American thinhorn sheep as a dis- net species,Ovis daZZi. ,At present,two subspecies of American ,.'Morn sheep are recognized.One is the '":The thinhorn group of North American 'sheep includes both 'the Dall's and Stone's sheep,found in Alaska and northwestern Canada.Both are wilderness animals resid- ing for the most part in spectacular alpine ,and subalpine mountain habitat.They are 'considered among the best of North America's trophy species;their horns and meat are highly prized by hunters.Because .tht!se sheep are highly visible in their white coats against the treeless green oftheir sum- ;Iller alpine environment,Dall's sheep in Particular are favored subjects of amateur and professional photographers alike.In $orne particularly accessible areas,Dall's eep are valued above all else for viewing d photography. ;i; '.:10. \. D ~:~.~ .,:~~~; ,};~ :",'1:'''.,'-:.'.-'S 2'1~~;':,J:'~.;...,':-71i : -~ii "I E· :I;iI..': c,~.. \.1~·~~i~",Ah}~'~~'.',"',",~,~- .......~'....\':,~,~, E,,·Y".\5;ic..;;"'~~'~-_",,~,'-:f!0 o~~k: [ lJ [....•" .-:1" ['-',:Co, .·fi:::t:\:;,:-.~.~.~"- [:.~:~, [' "-..,.: [1' [Big Game ofNorth America 174 lIe I5 Q ;.;..:~. ~,;~ '.'..~I.:·..t:I.·...·•.'''.',~-;r­.,.....",;;Lc,....., . '.~~/--," muzzles.They have white rump patches, bellies and rear portions of the legs. However,they may vary greatly in color, from nearly white to black.In both the Mentasta Mountains and the mountains northeast of Eagle in eastern Alaska,occa- sional sheep are found with gray or brown markings.Such color variations are more common in the northwestern part of Canada between the ranges of the true Dall's and Stone's sheep.These are Stone's sheep,for- merly called Fannin's sheep. The amber-brown horns of both Dall's and Stone's sheep are lighter in constuction than those of the bighorn sheep.Both sexes have horns which continue to grow throughout the animals'lives (Figure 36).Horns of rams are massive at the bases and taper to rela- tively fine tips.They grow in a spiral form as -~Y._~. ~'J-,.1'- c,~~\ \;:~~i •~....A.:,•..;;"..., •_ ~!::.?...",.....'-.....,i'-'-~«:..j....')~;.: DESCRIPTION The pelage of Dall's sheep consists of pithy,crinkled guard hairs with an under- coat of fine wool.It may be more than 5.1 centimeters (2 inches)thick in winter.The coat is typically all-white in color,although a few black hairs on the tail are not uncom- mon.Some newborn lambs have a consider- able amount of brown in their coats with a dark middorsal line and dark hairs on the brisket,tail surface and elsewhere.These neonatal coats are lost or overgrown shortly after birth.All lambs appear white within a week or two.Dall's sheep often appear yellowish or grayish due to staining of their white coats. Stone's sheep are typically dark brown or black with lighter-colored heads and white Young Dall's sheep ram (left)and mature ewe in winter pelage.Note black hairs in ram's tail and tIll,• ness ofcoat.Photo courtesy of the Alaska Department ofFish and Game. "~--"""-,_I ·'~'i.:C~.,,'>~'~."".,F !'f!~"'Sl .....-4....~......!~••""".... ._,;0:.......~.__.,_''.'.~'.-."L...1'".',......¥··...,.~·r..··{''''.M-''Ja,.'.,•._,,,,-."t.J~'"-:'."..'~...,....~...,"-"l'-";"._,~~J"'~.".•: ..,:1'-"'" ___.J ••- _'..,.',..:tr:>"?;'~v..k_~ G c D o c c [ E [ [ [ B [ [ o u ,,'".~'-.,;0 ..-.:••-~ Dall's Sheep '"w:t: 20~ 30~ ~Jl-....-----...-~-*--*-!.r',.--r ....Ho 80 20 100 : 0",~ffi60 ii~Lo ~:::.. ~ 175 Mature Stone's sheep ram in late summer pelage.Photo by Leonard Lee Rue III. viewed from the side.Outside diameters of the curls of adult Dall's rams'horns average about 27 centimeters (10.5 inches),and basal circumferences average about 36 cen- timeters (14 inches).Exceptionally large horns may have bases more than 36 centimeters (14 inches)in circumference. The average length of a full-curl ram's horns in Alaska is about 90.1 centimeters (35.5 inches);the largest recorded horns from a Dall's ram measured 123.5 centimeters (48.6 inches)in length.Most Alaskan rams have horns of three-quarter curl by age six and reach full-curl by about eight to nine years of age.Most rams attain about 90 percent of their potential horn growth (by volume)by the time their horns are full curl.There is considerable variation in horn size among Alaskan Dall's'sheep populations.This is believed to be related to "population quality"which,in turn,probably is de- pendent upon population density (Heimer and Smith 1975). rl.,rurc 36.Dall's sheep horn growth by age and ."t'X.Data courtesy of W.E.Heimer,Alaska De- p;lrtmcnt ofFish and Game. o,....<;,",'0 ,roj , · , · "''['.'" •~~d''"fw~'~_ 0 0o2 4 6 8 10 12 AGE IN YEARS "'- o [ o 9Ld c o c.-.~.C [ G c in B n>o [ t he [ IT [ II. Ir-e :[.':".~,.-1'_:.-;.~t'';",~,c~tj!:"';: [Big Game ofNorth America Mature Dail's sheep ram in summer pelage.Photo by Len Rue,Jr. [: [ [ [ c [. [J B c c b [ C [ L t Similar data on horn curl and age are not available for Stone's sheep,but in a sample of six horns from eight-year old rams,the average length was 90.5 centimeters (35.6 inches)(Geist 1971a).Measurements of the 50 top-scoring horns (using only right horn measurements)for both subspecies as listed in the Boone and Crockett Club's record book show an average length of 111.3 centimeters (43.8 inches)for Dall's sheep ,and 111.5 centimeters (43.9 inches)for Stone's sheep (Nesbitt and Parker 1977). Basal circumferences.s:,'eraged 36.3 cen- timeters (14.3 inches)and 37.1 centimeters (14.6 inches),respectively,suggesting al- most identical horn growth.The largest recorded set of horns taken from a Stone's ram measured 131.6 centimeters (51.8 inches)in length. Ewes'horns are much shorter,slimmer and less curved than rams'.In cross section, 176 female horns form a rather narrow oval, whereas ram horns are roughly triangular. A sample of 52 horns from female DaIL- sheep more than six years old averaged 2·l,;-, centimeters (9.7 inches)long (Heimer 197~, Nichols 1971).Stone's sheep ewes probably have horns of about the same length. Thinhorn sheep,like most northern ungu- lates,are heaviest and fattest in late fall and are lightest in spring after rigors of winter have taken their toll.A sample of 13 Dall'" ewes weighed in the fall averaged abou! 56 kilograms (124 pounds)(Nichols,l"l\ published),but exceptionally large ones m:i. reach 63.6 kilograms (140 pounds)or mu!", By later winter and early spring,avera:.:' weight in a sample of 45 ewes droPIH',: to about 48 kilograms (105 pounds),a 10,.- of 18 percent of average fall body weil-!h! (Nichols 1971).Data on fall weights of Dali- rams are scanty,but estimates place th, averag kilogr~ large kilogr~ nine a, averag poundf adult somew kilogrl indivi( (250 P' size di has no Mea Dall's centin timate six ye~ LIFE The with winte \'embl cessiv the pE found Lar l'~lrly llbout pears and a funct: notyl ofdat birth d liv birth thouf -Lal ,pOI.: their ilI"'l~l by f. .Octol ..~lt :-'dtnot [ [ [ [ 6 o o 8 o o G c c [ [ B average weight of adult rams from 82-100 kilograms (180-220 pounds)with some very large rams possibly exceeding 114 kilograms (250 pounds).A spring sample of nine adult Dall's rams in Alaska showed an average weight of 69.6 kilograms (153 pounds)(Heimer 1972).Average weight of adult Stone's rams is estimated to be somewhat heavier in the fall,from 100-104 kilograms (220-230 pounds).Exceptional individuals possibly exceed 114 kilograms (250 pounds).Whether or not a real weight- size difference exists among the subspecies has not yet been demonstrated. Mean height at the shoulder for nine Dall's rams more than six years old was 93.3 centimeters (36.8 inches),.,and 84.4 cen- timeters (33.2 inches)for 62 ewes older than six years. LIFE HISTORY The life cycle of thinhorn sheep begins with the rut,w}lich takes place in early· winter,generally extending from mid-No- vember to early December.For two suc- cessive years in Alaska's Kenai Mountains, the peak of rutting activity in one herd was found to be November 30 (Nichols,In press). Lambing occurs during late May and early June,following a gestation period of about 171 days.Chronology of lambing ap- pears to vary somewhat from year to year and among herds in Alaska.Whether it is a function of variation in the rutting season is not yet known.It may be merely an anomaly of data resulting from variable mortality at birth which,in turn,affects the numbers of living newborn lambs observed.Single births are the rule for both subspecies,al- though twinning occurs infrequently. Lambs weigh about 3.2-4.1 kilograms (7- 9 pounds)at birth and grow rapidly during their first summer,reaching an average weight of about 30.4 kilograms (67 pounds) by fall.Weaning usually takes place by October even though most lambs appear ca- pable of fending for themselves by two to three months of age.Lambs remain with Dall's Sheep their mothers during their first winter,and nursing occasionally may be observed dur- ing winter and even the following summer. There is some evidence on poor ranges in Alaska that many Dall's ewes nurse their lambs throughout the winter and only bear one lamb every other year (Heimer 1976).If these behaviors are general rules,they may function as adaptations to reduce the birth rate and increase survival of lambs born on depleted ranges.The sex ratio at birth is probably about equal,although the few data available suggest a preponderance of males (Geist 1971a,Nichols,In press). Yearlings of both sexes may be sexually mature by 18 months of age,although some do not mature until the following fall. Maturity in domestic sheep is related to physical condition and weight rather than age alone,and this may apply to wild sheep as well.If so,well-fed,larger individuals tend to mature faster than smaller,less ade- quately nourished sheep.Male yearlings, even though physiologically capable of par- ticipating in reproductive activities,seldom do.Dominance order among males prevents most rams from breeding until they are about seven years of age (Geist 1971a). Ewes and rams probably are capable ofre- producing throughout their life-spans.In several seasons of observing Dall's sheep during the rut,I saw no old rams which were not active participants.I collected two pregnant Dall's ewes which,from horn an- nuli,were estimated to be more than 13 years old.I also found one l5-year old ewe that died after giving birth.Another ewe,16 years old when captured and marked,was accompanied by a lamb.She was observed for three more years,but without lambs. During a study of a Dall's sheep herd in Alaska believed to h.ve reached or exceeded the carrying capacity of its range,all 18 adult ewes taken were found to be pregnant. Three of four yearling (18-months old)ewes collected also were pregnant (Nichols,In press).Thus,even under conditions of envi- ronmental stress,Dall's sheep can have a pregnancy rate of as high as 100 percent in adult ewes and,in this case,75 percent in 177 [t-t;,·[:l::~.;w..,,'. [Big Game ofNorth America "---~~ Threl' Dt-par ',i~..i1.;'J~ ~'=~' • "J'f.:.,,~·.,.. ·.~~·~ it 6.-:.~,..,t-,~~_..,r .. m Mo milill \he f :'wln~ .1nOre :""nt ;·-:rilll 1~~~g adults would be low and herd increase probably would occur.On the other hand,in a herd that has reached or exceeded its winter range's carrying capacity and thus faces a shortage of winter feed because of crowding and competition,pregnant females are unable to obtain sufficient nourishment to maintain their own physical conditions or enable optimum growth of fetuses.As a result,the pregnant ewe may experience fetal mortality through resorption or abor- tion to enhance her own chance of survival. Neonatal mortality,because of weakness and consequent hypothermia,and/or abandonment,also increases-sometimes drastically.Furthermore,surviving lambs may be small and grow slowly because of dams'inadequate milk supplies.They are poorly ,prepared to face their first winter, during which they may succumb in ,large numbers. Density-dependent natality factors appear to be the most important limiting factors af- fecting thinhorn sheep.These sheep usually occur at near-maximum densities in rela- tively stable,climax habitats which are sub- ject to harsh winters.The availability of food in these habitats may be limited severely by deep snow cover.Once a sheep herd reaches a certain density on its winter range, natural controls limit reproduction and sur- vival,and its population becomes stable or begins to decline. During normal winters and when snow remains soft,sheep are able to dig feeding craters down to good quality forage that is still green.Strong winds,prevalent in alpine winter ranges of thinhotn sheep. remove much of the snow from open ridges and slopes,exposing forage.By late winter. however,snow may be wind packed and im- penetrable.Sheep then are forced to depend on limited amounts of poor quality feed on the few,windscoured ridges that remalI1 snow free.At this time,sheep are in :I potentially negative energy-balance situ,,- tion;they may use more energy than thl'~' can take in feeding.From this time until spring,they depend heavily on stored bod.\ fat for nutritional needs.Body fat reserve~ MORTAUTY AND UMITING FACTORS Nutrition 178 A number of factors can affect the produc- tivity of thinhom sheep which,in tum,is a major determinant of herd status.In a herd with adequate winter forage,pregnant ewes receive sufficient nutrition to maintain their own physical condition and allow growth of fetuses to optimum size.Healthy,well- nourished ewes give birth to well-developed lambs and are able to provide them with ample milk,thereby assuring maximum production and early survival of young. Furthermore,these young grow quickly dur- ing their first summer and have a better chance of surviving their first winter.Un- der these conditions,expected mortality of yearling females.The effective natality rate-the number of lambs that survive long enough to be observed-normally is much lower than this,however.A ratio of only 20 lambs to 100 ewes was observed in the above herd the following spring,reflect- ing an approximate 80 percent loss from potential reproductive gains.Average pro- ductivity of Dall's sheep in Alaska was about 37 lambs per 100 ewes over a num- ber of years and within a number of herds (sample =57;standard error of mean =2.10).However,great variability among herds and years was noted-the • range was 8-81 lambs per 100 ewes. Life-span of a wild sheep is believed to be limited primarily by teeth condition and cor- responding feeding abill~y.The oldest Dall's ram skull found in a large series of naturally occurring mortalities in an overcrowded population was 12 years old at death (Murie 1944).Ewes tend to live longer than'rams. In addition to the aforementioned Dall's ewe that was captured and marked at age 16 and lived at least three more years,Geist (l971a)reported a Stone's ewe that reached 16 years of age. L L u B [ c c 8 [ c [ c [ o [ 'bJiG [Dall's Sheep [ [ ~':'," ,f.£'.~rj /'/;4-~~1:~~~"~../J'::!;:;)tI!~'..' .Ii '~::t..,-.;:,,4~••'C''.;L -;;/_.J·'tj.~:.:."-'r L :.:t:#;/("'("I .,)r',t ""r'~\....,..~~{.-,/.......':-.l.-tJ,j-I..".:'.,"'..,,~""........ ....1' ,Three Dall's sheep ewes feeding in pawed-out snow craters in early winter,Photo courtesy of the Alaska Department ofFish and Game. t ..-' ~,'i.~.' ~...~.4,'. .10'-' .,.:.... ·/1 .~ ~i--~·:;i;-. r-' ity !..;..- ....A· .../:·'1};~,:~... \ •I .",:.•/;,,,'.~IC',~,~._.'!~':"A1',,~:.::',;''.r~-~~-".'..~~:. ~"<., .",.1,1) " I t' h _,),I.,.r. r.."..;-...,.~o·J...--l./.~i ....l ' .:;f'~~?~",'ilr/ifr ' w"~'1A1':';,( -{:.v :....~:.{ ...."":.: ; ~..,.. '\ , 1..J ~{.-,;,. .( -;::.... r--' ,(;:','~..i.~f:.",~ ._~,'~~'---"'~,;.;,-.,:"",.,';"".-_''*t-..'-~~~'..~,.-.'" o} /..:~I·.~~l,t'-,".,c'..,'t~ :. A C (J 6 [ 8 [ [ c B [ u L [ decline rapidly;the last to be catabolized are those stored in the bone marrow.Both lambs and yearlings,with limited fat reserves,suf- fer more than adults do (Figure 37), Mortality among lambs surviving the initial rigors of birth normally is very low the r:rst summer but high during the first winter,reaching about 40-50 percent or more iIi stable or declining herds.The winter of their second year is another critical period in the lives of northern sheep, Much of a yearling's summer nutrient in- take supports growth rather than being stored as fat,and nutrition is not supported by mother's milk.Therefore,yearlings are more vulnerable to nutritional scarcity in winter than are adults,Few data are avail- able on mortality rates of sheep in their second winters,but those rates appear to ap- proach 15-20 percent. After sheep are two years old,mortality rates decrease,presumably because their physiological growth rates decline and more nutrition is available for the production of fat reserves needed during winter.Geist (1971a)found that bighorn sheep mortality averaged about 4 percent per year from ages two to seven,then increased to 23 percent per year thereafter.Murie's (1944)data in- dicated a similar pattern for Dall's sheep. E 179 [,(0'"~.lJ [Big Game ofNorth America 180 Figu llhec ofw win lhir' InftE Ul 200- :5 CD ::Ii :J Z......::..100· 300l \ cellenf E of smeI: threats gers.Tl very ac' somewh environ natural Althc bears,~ sionall~ serious wolf.A capturi they dl fluencE popula be we~ foodsc Fro:r: proted McKir crease proxin Avera percer sula 1 (FigUl Thinhorn sheep are capable moun- taineers,able to negotiate rugged terrain with speed and grace.They depend on this terrain for protection from predators.Ex- Disease,such as actinomycosis,and parasites including lungworms and gas- trointestinal nematodes are present in northern sheep,but have not been shown to be main causes of any herd declines.Neilsen and Neiland (1974)suspected,however,that gastrointestinal nematodes in particular may contribute significantly to spring mor- tality because of the coincidental "spring rise"in internal parasite loads and weakened condition of sheep at that time.It is probable that parasite infestations and disease exert more influence on sheep sur- vival during times of maximum population density and environmental stress than dur- ing other times. Predation Disease and parasites severe winters.These were not winters of exceptional cold,but of above-normal temperatures and more-than-usual preci- pitation.During normal winters,snow re- mains light and fluffy and is blown free of alpine feeding areas.Wet snows,or thaws and subsequent refreezing,fix snow in place with a hard crust,preventing removal by wind or digging by sheep.Snow depth and hardness,maximum winter winds and temperatures the previous winter are cor- related inversely to lambing success (Murphy 1974,Nichols 1976).The in- ferences are that lambing success is depressed by deep and hard snow,above- freezing temperatures lead to crusting,and high winds along with thawing tempera- tures pack snow to rock hardness.Dall's sheep are adapted to continuing cold,high winds and normally light snowfall of winters in northern interior mountain ranges. el '" 60 40 20 ~9 _L~_/~~ Adult i o I , , , ,i , , , ,I 8 9 10 11 12 1 2 3 4 5 6 MONTH 140 20 100 20 I , ,i'i'"I 8 9 10 11 12 1 2 3 4 5 6 MONTH Figure 37.Changes in Dall's sheep weights and percentage fat in bone marrow by month and age classes.Least squares curves fitted to data from a series of sheep collected in the Kenai Mountains, Alaska (after Nichols,Unpublished). 100 ...80<LL ~0a::a::<:::E...zw (,Ja::w 40'" At present,the main influence on thinhorn sheep numbers appears to be winter weather.Exceptionally severe winters may cause drastic "crashes"in sheep numbers regardless of population densities or range conditions.Successiva severe winters occurred in Mount McKinley National Park,Alaska,between the late 1920s and the mid-1940s and probably elsewhere in the state.Unusually deep and crusted snow resulted in high mortality,and herds dropped to a fraction of their former abundance.Other,more localized declines have since been documented following ... :I: el al ~..J60 Winter weather [ b [ [ 6 q,'[3 [ c u G o ~ c [ [ L Dal!'s Sheep Figure 38.Increase patterns of three Dall's sheep herds in the Kenai Mountains,Alaska,two of which (Surprise Mountain and Crescent Moun- ~in)were heavily hunted for rams,while the third (Slaughter Mountain)was closed to hunting (after Nichols 1976). cellent eyesight and a well-developed sense of smell enable them to detect potential threats before most predators become dan- gers.The hearing of sheep appears to be very acute,but this sense may be heeded somewhat .less than others because sheep environments often are disturbed by such natural sounds as falling rocks. Although coyotes,wolverines,lynx,black bears,grizzly bears and golden eagles occa- sionally take adults and lambs,the only serious predator of thinhorn sheep is the wolf.Although wolves have been observed capturing sheep both in summer and winter, they do not appear to exert any major in- fluence on sheep numbers except in times of population overabundance,when sheep may be weakened or forced by competition and food scarcity to feed.far from escape terrain. From 1947-1961,when wolves were protected and presumably abundant,the McKinley National Park sheep herd in- creased at an average annual rate of ap- proximately 11 percent (Murphy 1974). Average annual increase rates of 11-14 percent were observed in three Kenai Penin- sula herds where no wolves were present (Figure 38). I FinED POPULATION GROWTH CURVES,/ THREE DALL'S SHEEP HERDS / / I . ,II //,/. CRESCENT MT.~,//.... ""SLAUGHTER MT. /,.,"7 /''/,,,"/.,' ,,/'/'"'--SURPRISE MT.,. ,,;,/./__-,,0 BEHAVIOR 181 Accidental falls take a small number of sheep,as do avalanches and other accidents. Nevertheless,it is winter weather which- by restricting both food supplies and move- ments-exerts the only known mortality of significance to thinhorn sheep populations at the present time. In general,sheep are diurnal,although some movement may occur at night.Sum- mer daylight in the North is long,so sheep may be found moving or feeding at almost any time.Major feeding periods generally occur during early morning and late afternoon with occasional shorter periods of grazing activity about mid-day.Much of the time between feeding is spent resting and ruminating.Preferred resting sites, particularly at night,are on or very close to cliffs or large rock outcrops which serve as escape cover.Daily movements generally consist of moving out of rugged t"!rrain to preferred feeding areas in the morning,then drifting back before dark.During the short winter days,morning and evening feeding periods are interrupted by a brief midday rest.Most rumination probably occurs at night when feeding and movement are rela- tively difficult. During summer,thinhorn sheep may move considerable distances from winter home ranges to occupy nearly all suitable alpine habitat in an area.By late summer, they begin to drift back to wintering ranges, where they congregate before the rut begins. Winter range usually is a small part of the overall range and is limited by snow condi- tions to those areas where snow-free feed- ing sites and escape terrain lie in close proximity.In early spring,sheep usually move lower on slopes,often into the upper limits of subalpine timber.They seek the first emergent green vegetation when snow lines begin to recede.Sheep move upward with the receding snow line until they are free to leave their winter-spring ranges. Accidents 197319681963195819491953 ~l r 200 I I ~ 1,00 L G o [ c o [ c [ [ 6 c [ [ B B [Big Game ofNorth America Mid-day rests between morning and evening feedings are common during short winter days.Photo by William E.Ruth. Aftl sexes seek t they 1 as th tions whid rangE quen1 DuriI follov time, year- andf may geogJ sepal thes, So mem vela! \'olvl mair base arno the' Dall's, just p courte Game. pregnant ewes leave their past year's lambs and seek isolation in the most rugged ter- rain available,where births take place. They remain there for several days follow- ing parturition (Pitzman 1970).They then move away from lambing cliffs;which usually are merely part of the spring range, and join other ewes with new lambs.Mean- while,abandoned yearlings frequently form small groups which follow one or more bar- ren ewes.Frequently male yearlings begin to follow older rams. Nursery groups,consisting of ewes with new lambs and occasional yearling females, persist for a few weeks after parturition, then gradually merge with groups of barren females and yearlings to form loose herd associations that occupy summer ranges. The basic unit of these groupings is a lactat- ing ewe,her lamb and frequently her year- ling female.However,some male yearlings remain with ewe-lamb combinations. 182 Where summer and winter ranges are contiguous,annual movements can be characterized as dispersal over all suitable habitat during summer,and withdrawal to smaller areas that provide necessary winter habitat.Actual migrations may occur along traditional routes in spring and fall where summer and winter home ranges are sep- arated by unsuitable habitat such as forests or wide river valleys.Visits to mineral licks are an important part of winter-to-summer range movements of Dall's sheep.Sheep, especially ewes with lambs,may linger in the vicinity of licks for days,M'eeks or even much of the summer.Heimer (1974)and Geist (1971a)reported high incidence of in- dividual adults returning to their previously occupied seasonal ranges year after year. Sheep society centers about two basic groupings:maternal ewe,lamb and yearling groups which often merge into larger herds; and ram groups.As parturition approaches, G [ L c c [ flIS c fl..;U· o o o [ [ [ [ [ [ [ [ c~...c o .. G ~ to ~ c G [ G [ L c Dalt's sheep ewe seeks solitude and rugged terrain just prior to parturition in the spring.Photo courtesy of the Alaska Department of Fish and Game. Mter the rut,during which all ages and sexes are intermixed,older rams usually seek the company of other rams even though they may remain on the same winter range as the ewe groups.As soon as snow condi- tions permit in the spring,groups of rams which have begun congregating on spring range move toward summer range,fre- quently assembling in large groups en route. During these movements,smaller rams follow the largest ram in the group.At this time,many yearling rams and most two- year-old rams leave the association of ewes and follow older rams.Rams'summer range may overlap that of ewes'or may be geographically separate.Most rams remain separate from ewes even when occupying the same areas. Social behavior,like that of other members of the genus Ovis,is well-de- \'eloped in thinhorn sheep.Ram behavior re- volves about the establishment and maintenance of a dominance hierarchy based on the size of horns.Interactions among rams,including horn displays and the well-known clashing,may become quite Dall's Sheep complicated and occur throughout the year except during stress conditions of late winter. Sheep interactions are well-documented by Geist (1971a).Rams determine and main- tain social orders with limited confusion and damage to individuals through visual rec- ognition of each other's horn size-dominance status.Large-horned rams are socially dominant,treating all smaller individuals as "females,"while small-horned rams are aggressive toward dominant rams.Ewes are largely ignored by rams since they react passively except during estrus periods. When in estrus,ewes behave somewhat like small males and encourage social and sexual behaviors by adult males.During the rut, the established dominance pattern between rams may be disrupted temporarily when a ewe comes into estrus,with all nearby classes of mature rams jostling and clashing for possession of the ewe.Possession is es- tablished quickly by the largest ram,who then remains with the ewe through her ap- proximately one-day estrus,defending her against other rams and breeding her repeatedly. Rams neither maintain territories nor gather harems.Instead,they seek out one ewe at a time and eventually leave her at the end of her one-day estrus for another. They travel widely among ewe groups just before and during the rut seeking receptive females.Although sexually mature at 1.5- 2.5 years of age,rams generally do not be- come behaviorally mature and participate seriously in reproduction until the age of 7 (Geist 1971a).Where mature rams are removed from a herd through hunting, younger males become sexually active.In at least one Alaskan herd of Dall's sheep,all rams with horns of three-quarters curl (about six to seven years of age)and older were removed by hunting for a number of years (Nichols 1976).The remaining young rams in the four-to-six year age classes car- ried out all rutting activity,behavior in which they would not normally be allowed to participate.The rates of increase in this herd and another nearby herd subject to 183 r,c<t,r:.·~;;;C~,-~ [Big Game ofNorth America Clashing or horn displays among rams may occur at slightest provocation during much ofthe year as well as during the rut.Ram on right provoked this short-lived clash to take over a hollowed out resting site. Photo by William E.Ruth. [ [ [' [ D o [J 6 D c B [ c [ L c similar hunting pressure and age structure were nearly the same as that of a third herd which was not hunted.The results infer lit- tle short-term effect on the rate of reproduc- tion by the removal oflarge rams. Serious formal clashes generally occur only among rams of nearly equal horn size and who are unable to identify each other's dominance status.Clashing and other breeding and social interactions appear to be less intense among Stone's rams than among bighorn rams,and even less intense among Dall's rams than among Stone's rams.This circumstance may be an adapta- tion to conserve energy resources of species facing long and severe winters in northern latitudes. Ewe social behavior is much less apparent than that of rams.Except during the estrus period,it consists of little more than ma- ternal treatment oflambs and occasional ag- 184 gressive behavior towards others for space or food,as well as banding together loosely for.companionship.Lambs interact fre- quently in play,running and jumping, and in the learning process,they exhibit many of the behaviorisms of adults.On occa- sion,adults will run and leap in play for short periods. HABITAT Dall's sheep habitat is typically alpine: steep,opel:'grasslands interspersed with broken cliffs and talus slopes on recently glaciated mountains.It usually lies almost entirely above timberline which,in Alaska. is variable in elevation but averages about 765 meters (2,500 feet)above sea level. Winter snowfall is comparatively light,av- eraging 31.9 centimeters (12.5 inches)over a five-year period on three Kenai Mountains sheep r normal winter, andslo: Vege bunchg crowbe and m( of sheE dwarfl and c thicke1 extend sheep twiste( white ~ StOll subalp recent cipitat are fe' of tht thicke Engel comm Bot] anim~ plant~ herds sedge of thE brow~ chens good is aVl plant varie forag arnot total mer adeq whic late cate< coml that mail In and [ [1]'1 k:l·...1 [ ..~:i-t ,~~ .:1 9 0-~1'...... ~.. '!.~ ~~"" . .:.~l~·..J:~l..........i-*... :~'.~~a..·.. .j'f'1 ..~.:~.....: l~";;:\' Il<~Bwell 7g sitl', ~pac(. oosely A .fr!'. 6nng. ~xhibit r~.,cca.B for [ llpine n.Vith tJnth IImo:'1 ('3~-;ka, clOU t <!ivcl. It.'lV- fjt'r;, Uun,.. c sheep ranges (Nichols 1976).Temperatures normally remain below freezing during the winter,and high winds sweep many ridges and slopes free of snow. Vegetation consists largely of sedges, bunchgrasses,low shrubs such as blueberry, crowberry,dwarf willow,mountain avens, and mosses and lichens.The lower portions of sheep habitat may have large stands of dwarf birch interspersed with larger willows and dense alder and alpine hemlock thickets.In some places where broken cliffs extend suitable habitat below timberlines, c sheep utilize benches supporting stands of . twisted cottonwood,aspen and occasional white spruce. Stone's sheep habitat is somewhat more subalpine in nature,and in mountains less recently glaciated and with higher pre- cipitation than Dall's sheep habitat.There are fewer open alpine grasslands,and much of the higher slopes are covered with thickets of dwarf birch and alpine fir.Aspen, Engelmann spruce and lodgepole pine are common. Both subspeCies are primarily grazing animals,although many forbs and browse plants are eaten as well.A study of three .herds of Dall's sheep in Alaska found that sedges and bunchgrasses made up the bulk of their diet,followed by lesser amounts of browse (mainly dwarf willow),moss and li- chens (Figure 39).During summer,forage of good nutritional quality and great diversity is available.Sheep eat a greater variety of plants in summer than in winter when the variety,quantity and quality of available forage are reduced greatly.As indicated by amounts of crude protein,gross energy and total available carbohydrates in their sum- mer diets,Dall's sheep obtain more than adequate nutrition during that season- which allows them to accumulate fat.By late winter,however,diet quality,as indi- cated by the relative amounts of the same components,deteriorates to a level below that presumed necessary for physical maintenance. -In addition to suitable climate,terrain and food,mineral licks appear to be nec- Dall's Sheep Figure 39.Diet of DaB's sheep in Alaska (after Nichols,Unpublished). essary components of Dall's sheep habitat. Licks are found on most of Alaska's sheep ranges.Use is highest in late spring and early summer,and diminishes by late sum- mer.Some licks are quite large;one serves a population of about 1,500 sheep that travels as much as 19.3 kilometers (12 miles)to the lick (Heimer 1974).Hebert (1967)found that sodium was the element most sought in natural licks by mountain goats.He sug- gested that lick use was the result of a high water intake on a low sodium diet (initiated by feeding on succulent forage in the spring) rather than a winter dietary deficiency. Geist C1971a)suggested that sheep use licks to replace skeletal minerals lost through ca- tabolism during winter. MANAGEMENT Distribution and status 'In Alaska,Dall's sheep occupy suitable habitat in the Brooks Range,the Alaska Range from the Canadian border to Lake Clark,the Wrangell Mountains,the Chu- gach Range,the Talkeetna Mountains and parts of the Kenai Mountains.Small 185 [:r:~[Big Game ofNorth America Small 200 aniI corner of Stone's Stikine Cassiar, north of· Stone's Market in past ~ haverec or possi are har quarter seven-ei ofRock~ heavyh ment of tor con1 has bee ranges. In g sheep i the pri] to hunt not be thinhOl produc1 reduce sive ra of avai that if out OVI genetil small-: yet bE dence breedi tion aI Reci limiti] from minin shoull while ~ent hunti nnd n possii alter: 67 68 69 70 71 72 73 74 75 YEAR British,Richardson,Warnecke,and Ogilvie mountains.An estimated 18,000 Dall's sheep occur in the Yukon Territory,and populations are believed to be generally sta- ble.Stone's sheep are found in relict popula- tions in the Cassiar,Pelly and Selwyn mountains,and the Salmon Range;a few oc- cur in the Ogilvie Mountains.There are some 4,500 present,mostly in small and scattered bands.Populations are thought to be relatively stable (Hoefs 1975).Both subspecies are hunted under the three- quarter curl regulation,with one ram per hunter per year allowed.Guides are re- quired for nonresident hunters,and natives are allowed unrestricted hunting of both sexes.The estimated annual harvest of thinhorn sheep in the Yukon Territory is about 250 rams. From 3,000-8,000 DaIl's sheep are esti- mated to inhabit the MacKenzie Mountains in the Northwest Territories (Stelfox 1975). Populations are stable.As elsewhere,non- residents must hire a guide,and hunting by natives is unrestricted.Approximately 150 rams are taken annually under the three- quarter curl restriction,with one ram per non-native hunter allowed each year. Figure 41.Dall's sheep harvest statistics in Alaska,1967-1975. NORTHWEST TERRITORIES ~Q daJ/idaHi ~0 doll,stonel 186 isolated herds are found in the White Moun- tains and Tanana Hills north and east of Fairbanks (Figure 40).Estimates place the state's population from 30,000-50,000 sheep.Early market hunting and possibly hunting by natives depleted a few local herds which appeared to recover by the 1920s.In response to a series of severe winters,a major decline apparently occurred in the 1930s and early 1940s,leaving many of Alaska's sheep populations at very low levels.Since that time,herds have recovered and now appear to have stabilized in most areas while declining gradually in a few others (Nichols 1975). Management in Alaska mainly has con- sisted of allowing only the harvest ot rams with horns of three-quarter curl or larger in annual August-September hunting sea- sons.Nonresident hunters are required to have a licensed guide.One ram is allowed per hunter each year.Approximately 1,000- 1,200 rams are harvested annually (Figure 41).Recently initiated management prac- tices include establishment of restricted ac- cess areas and full-curl ram-only hunts as well as limited either-sex hunts. In the Yukon Territory,Dall's sheep are found in all ranges between the Yukon River and the Alaska border to the west and the British Columbia border to the south. They occur north of the Yukon River in the Figure 40.Current distribution of Dall's and Stone's sheep. u G [ Q o ~.'.."..•.L c [ [ [ [ [J [ E E E [ [ [ [ [ 6 o D B Q c E c D c c c Small herds of Dall's sheep totaling about 200 animals are found in the northwest corner of British Columbia (Demarchi 1975). Stone's sheep occur on the Yukon and Stikine plateaus,and in the Skeena, Cassiar,Omineca and Rocky mountains north of the Peace River.From 9,000-15,000 Stone's sheep inhabit British Columbia. Market hunting reduced some populations in past years,but most herds are thought to have recovered and now are relatively stable or possibly declining slightly.Most herds are harvested on the basis of the three- quarter curl,ram-only regulation,but a seven-eighths curl law now applies to rams of Rocky Mountains populations.Relatively heavy harvests have decreased the male seg- ment of some accessible herds.Also,preda- tor control,primarily poisoning of wolves, has been u.ndertaken in some Stone's sheep ranges. In .general,management of thinhorn sheep in both Alaska and Canada has had the primary objective of furnishing trophies to hunters.Harvesting only adult rams has not been shown to adversely influence thinhorn sheep populations'capacity to re~ produce,nor is it effective to control or reduce herd numbers where desired.Inten- sive ram-only hunting reduces the number of available rams.Some individuals contend that if selective ram-only hunting is carried out over a long enough time,there may be a genetic effect in selecting for the survival of small-horned males.However,this has not yet been demonstrated.Accumulated evi- dence reported earlier in the chapter shows breeding by young rams and herd reproduc- tion are not reduced. Recent innovations of controlling access, limiting numbers of hunters harvp.sting from select herds,and increasing the minimum size of rams to be harvested should have even less impact on populations while increasing opportunities for enjoy- ment of recreational hunters.Controlled hunting of ewes will enable manipulation and management of sheep herds by making possible control or reduction of populations, alteration of sex ratios in favor of rams,and Dall's Sheep improvement of reproduction and survival rates in overcrowded herds.In addition, need has been recognized in both Canada and Alaska to set aside certain sheep herds for nonconsumptive uses,such as viewing, photography and scientific study. Estimating populations Because of the size and ruggedness of sheep habitats,aerial surveys are the most economical and efficient way to evaluate population status.Thinhorn sheep can be classified by sex and age classes on the basis of horn and body sizes and conformations. Aerial surveys are applicable especially to Dall's sheep,which reside in treeless alpine regions and usually are highly visible in the summer.Light,fixed-wing aircraft are rela- tively economical and can provide the means of determining distributions and population sizes with fairly high degrees of accuracy. Using fixed-wing aircraft to determine sex and age classes is possible also,but requires considerable flying and observing skills. Use of helicopters allows for more ac- curate surveys,but generally is eco- nomically impractical except under special circumstances.Also,sheep react more to low-flying helicopters than to small air- planes-a harassment factor that must be considered,especially when young lambs are present. Use of ground surveys to examine samples of a herd,combined with aerial surveys to estimate total herd size and distribution, generally is preferable to exclusive use of either aerial or ground surveys.Because rams usually are not with the ewe bands after lambing,detailed sex-age classifica- tions are best conducted just prior to the lambing season.The objective is to obtain the best ram-ewe and yearling-ewe ratios and ram size class estimates before the ram portion of the herd becomes segregated.Dur- ing aerial surveys conducted just after lamb- ing,the proportion of new lambs (which are readily visible from the air)and total herd size may be estimated effectively.Popula- 187 [ [ L [ [ E c G B ~ c B [ [ [ L E Big Game ofNorth America tion models then may be constructed mathematically by combining results of both surveys;and population parameters- such as reproduction,survival,and herd composition-may be estimated (Nichols 1970). Up close,thinhorn rams may be aged ac- curately by their horn annuli (Geist 1966, Hemming 1969).These annuli,reflecting a cessation of horn growth each .fall,are readily visible to the trained eye.They may be used to estimate age of carcasses or just horn specimens to within about one month if the date of death is known.Ages of ewes also may be estimated from horn annuli,but more careful examination is required be- cause these annuli ,are closer together and•difficult to distinguish in older-aged spec- imens. THE FUTURE At present,Dall's sheep in Alaska and Canada have no serious man-related habitat problems.They inhabit rugged and remote terrain,for the most part inhospitable to man.However,the future may bring several types of human activity that c()Uld cause habitat damage or reduction.The well-pub- licized trans-Alaska oil pipeline has already pushed a road through the heart of sheep habitat in the formerly remote Brooks Range.The road does no significant damage in itself,but undoubtedly will open the area to further 'mineral exploration and possible development.Harassment of sheep by heli- copters during mineral exploration already is common in many ranges.Mineral development in sheep habitat may affect sheep populations adversely by severely disturbing habitat and forcing sheep to abandon vital ranges.One major mineral lick already has been staked out (but not developed)as a mineral claim.A planned hydroelectric project on Alaska's Susitna River,although probably doing no damage to sheep habitat in itself,will open here- tofore remote sheep ranges to boat traffic and possible further development. 188 The greatest danger facing Dall's sheep in Alaska is a plan now being considered to open large tracts of sheep habitat to grazing by domestic livestock,including domestic sheep.Should this materialize,wild sheep populations may be depleted as a result of competition for forage and diseases brought in by livestock. In Canada,Stone's sheep already are faced with loss of habitat to a large hydroelectric project as well as to mineral developments.A railroad has been con- structed through the heart of sheep habitat and a highway is planned,both of which will open sheep ranges to further ex- ploitation.A potential problem facing both Dall's and Stone's sheep in northern Canada is the increasing commercial value of their horns and capes.Since natives have no restrictions on the number of sheep they can kill,there is a potential for wholesale destruction of populations.A management approach is needed immediately to permit use of sheep populations only within bio- logical limits. Although not necessarily harmful to sheep,large tracts ofland will bl;)withdrawn soon from unrestricted public use under the Alaska Native Claims Settlement Act.In- cluded will be large blocks of sheep habitat probably set aside as national parks on which all hunting will be restricted,and large areas to be under the control of private,native corporations,on which the future of sheep hunting is unknown as yet. These withdrawals not only will remove presently available sheep herds from public hunting,but will concentrate hunters on the remaining open lands.This undoubtedly will necessitate more intensive manage- ment and restrictive harvests. The most important future need of thinhorn sheep will be habitat protection. This will require Ii herd-by-herd inventory of critical sites,including mineral licks, lambing and wintering areas,and migration routes.Once known,these sites and the sheep that use them will need protection from human development and undue harassment.Unless undertaken promptly, such form Co vital ecolo date time. of st [ [ [ [ [ o c b B A.JB c B [ u [ l c such habitat protection may come too late for many sheep populations. Continuing and long-term research is vital to understanding of thinhorn sheep ecology and management needs.Research to date has been limited in scope,area and time.In particular,comparative studies of sheep occupying different habitats are Dall's Sheep needed.To make more efficient use of the thinhorn sheep resource,management policy makers will have to provide more money and manpower for sheep manage- ment and research,and managers will have to make better use of modern management techniques and research findings. 189