Black Bear Monitoring in Eastern Interior Alaska

BLACKBEAR MONITORINGIN EASTERNINTERIOR ALASKA

MARK R. BERTRAM,U.S. Fish and Wildlife Service, Yukon Flats National Wildlife Refuge, 101 Twelfth Avenue, Fairbanks, AK 99701, USA, email: [email protected] MICHAELT. VIVION, U.S. Fish and Wildlife Service, Yukon Flats National Wildlife Refuge, 101 Twelfth Avenue, Fairbanks, AK 99701, USA, email: [email protected]

Abstract: Americanblack bears (Ursus americanus) are common predatorsof ungulatesin interiorAlaska, yet little researchhas describedbear demographics. This study examines movement, denning, and reproductivecharacteristics of a black bear populationin the YukonFlats in eastern interiorAlaska. To our knowledge, this location at 66&Nlatitude is the northernmoststudy of black bears. A total of 29 ind ividual black bearswere captured53 times between 1995 and 1997. Capturerates were high with a mean annualrate of 2.3 black bears/I0 trapdays. A total of 900 telemetry locations was obtainedfrom 23 radiocollaredblack bears. Mean annualhome rangesfor adultfemale and male black bearswere 15.5 and 182.5 km2, respectively. The mean date of den entry was 26 September(range: 19 Sep-8 Oct, n = 42) and the mean date of den emergencewas 2 May (range: 26 Apr-6 May, n = 31). Mean length of denning exceeded all previous reportsat 220 days (range: 213-229 days, SD = 4, n = 31). Females excavatedall dens in well drainedterrain in forested areas. Mean litter size for 7 adultfemales was 2.1 (n = 10). The recruitmentand reproductive intervalswere 2.0 years (n = 2) and 1.6 years (n = 5), respectively. The survival rate for cubs weaned to 1 year was low (0.45). The mean annual survivalrate for adult males was 0.86. We report2 likely instanceswhere, duringspring, grizzly bears(Ursus arctos) preyedon adultfemale black bears with young.

Ursus 13:69-77 (2002)

Key words: Americanblack bear,denning ecology, interiorAlaska, northernboreal forest, reproduction,survival rates, Ursus americanus

The range of the American black bear extends over 147,231W)and about 35 km south of the Arctic Circle. much of North America includingall or partof 38 conti- The YukonFlats is a vast wetland basin bisected by the nental states, 7 Mexican states, and much of Alaska and Yukon River. The basin is underlainby discontinuous Canada(Beecham and Rohlman 1994). The northernlimit permafrost and includes a complex network of lakes, of theirrange is found in Alaskanear the BrooksRange at streams,and rivers. The landscapeis heavily influenced the terminusof the northernboreal forest. Records of by flooding and wildlandfire. Due to the areais low an- black bear north of the Brooks Range are rare (Bee and nual rainfall, high summertemperatures, and high inci- Hall 1956). Few studieshave beenconducted of blackbears in north- ern latitudes. Previous work has described regional de- mographicsand specifically examined the influence of environmentalfactors on denningecology and reproduc- tive parameters(Tietje and Ruff 1980; Schwartz et al. 1986; Kolenoskyand Strathearn1987; Miller 1990, 1994; Smithet al. 1994). This workhas provideda broadframe- workto begin to understandblack bear biology in Alaska. Herein,we describeseasonal use patterns,den site char- acteristics,denning chronology, and reproductive and mor- talityparameters of blackbears in the northernboreal forest of eastern interiorAlaska. To our knowledge, at 66oN latitude and approximately 35 km south of the Arctic Circle, this is the northernmostblack bear study. We presentthese findings to better describe extremes in the black bearis range.

STUDYAREA The 16,835 km2study area was located in the western YukonFlats in the northernboreal forest of easterninte- rior Alaska (Fig. 1). The study area encompassed the Yukon Flats National Wildlife Refuge and included the westernhalf of the Alaska of Fish and Game Department Fig. 1. Study area for black bear in Interior Alaska, 1995-97, (ADF&G)Game ManagementUnit 25 D. It was situated including major lakes (in gray). Bears were captured at lakes 35 km east of the village of Beaver, Alaska (66*211N, marked 1 and 2 on lower figure. 70 Ursus 13:2002

dence of lightning,fire activity is often intense and wide- was definedas a baitedsite with >1 active snaresfor a 24- spread. Since 1981, the YukonFlats region has had 256 hourperiod. fires bur over 2.5 million acres, averaging510 km2/year Black bearswere immobilizedwith Telazol(A.H. Rob- U.S. Fish and (PerryGrissom, WildlifeService, Fairbanks, ins Company,Richmond, Virginia, USA; 300 mg/ml at Alaska, USA, unpublisheddata). The southernedge of 0.005ml/estimated kg of body weight) and fitted with the studyarea includes uplandsand foothills of the White model 500 expandablebreak-away radiocollars (Telonics Mountains,with elevations rangingfrom 91 to 912 m. Inc., Mesa, Arizona,USA) containinga motion-sensitive The areawas characterizedby mixed forestsdominated mortalityswitch (12.5 hourdelay). Black bearscaptured white by spruce(Picea glauca), blackspruce (P mariana), in 1997 were fitted with radiocollarsdesigned to drop-off paperbirch (Betulapapyrifera), quaking aspen (Populus after several years of use (Hellgren et al. 1988). Button tremuloides),and balsampoplar (P. balsamifera). Shrub Duflex tags (NationalBand and Tag Co., Newport, Ken- communitiesof alder (Alnusspp.) and willow (Salix spp.) tucky, USA) were attachedto each ear. A unique right- are most common in ripariansites and edges surrounding left combination of brightly colored heavy vinyl was lakes andmeadows. Dwarfshrubs such as glandularbirch pressedbetween ear tags to assist as visualmarkers. Black (Betula glandulosa), Labradortea (Ledumdecumbens), bears were permanentlymarked by a right upperlip tat- crowberry(Empetrum nigrum), and blueberry (Vaccinium too. uliginosum)were common in the uplands. Standardmorphometric data including body weight The Yukon Flats has a continental subarctic climate were recorded. In addition,pelage color and condition characterizedby large seasonal extremes of temperature and any distinguishing marks, scars, and injuries were anddaylight. Summertemperatures can exceed 38?Cand recorded. A vestigial premolar(PM1) was extractedwith are warmerthan any other comparablelatitude in North dental pliers and age was estimatedusing cementuman- America. The mean minimum Januarytemperature is nuli analysis(Willey 1974;Matsons Lab, Milltown, Mon- -33?C with wintertemperatures reaching -59?C or lower. tana,USA). Mammaryglands and vulva were examined Althoughthe areahas a shortgrowing season of about81 to determinefemale reproductive status. Blood was drawn days, the long hoursof sunlightduring the springand sum- from femoralarteries and latertransferred to freezerstor- mer monthsproduce abundant vegetation. The mean an- age and analyzedfor Toxoplasmagondii, a parasiticdis- nual precipitationis 16.7 cm, ranging from 9.1 to 27.2 ease carriedby domestic cats thatcan cause birthdefects cm. Snow accumulationsrarely exceed 76 cm. in humans (ADF&G, Fairbanks,Alaska, USA). Black The Yukon Flats Ecoregion was largely unexploited, bearswere classified as cubs (0-1 yr), yearlings(1-2 yr), included no significant development, and was roadless subadults(2-4 yr), and adults (>4 yr). with only air and watertransportation available. The re- gion was settledby 3 villages of KutchinAthapaskan with Monitoring populationstotaling approximately 250 individuals.Black Black bears were located from 1995 to 1997 by fixed- bearhunting was not a traditionalsubsistence activity, thus, wing aircraftat approximately10-day intervalsbetween hunting pressure was light. During the study period, a mid-April and early-October. Telemetry data included licensed guide used the areaand harvestedup to 10 black latitude and longitude of location, activity pattern,and bearsannually. habitattype. Den Investigations METHODS The reproductivestatus of adultfemales was monitored annuallyfrom early Marchto early April 1996 to 2001. Capture In most instances, we were able to gain close access to Bears were capturedat Beaver Creek and near 2 adja- den sites (<0.5 km) with a ski-equippedfixed-wing air- cent lakes (Fig. 1). Aldridgefoot snares were anchored craft. Females were immobilizedin the den and cubs, if to maturepaper birch or white spruce trees (minimum6 present,were counted, sexed, and weighed. Yearlingfe- inches diameter)and vegetation was cleared in a 3.6-m male cubs were fitted with a radiocollarand the rightup- (12-foot) perimeteraround each tree. Traditionalcubby per lip was tattooed. Adult females were weighed, and sets (Beecham and Rohlman 1994) were constructedat radiocollarswere replacedevery 2 years. the treebase andwere baitedprimarily with chum salmon Physicalcharacteristics of each den site were measured, (Oncorhynchusketa). Up to 4 snareswere placed at each including the location, structure,and aspect of the den site. Bait sites were monitoreddaily in 1995 and twice and the snow depth. We also measuredthe height, width, daily in 1996 and 1997. Trappingeffort was expressedin and depth of the entrancehole and the den chamber. En- bears capturedper 10 days of trappingeffort. A trapday trance and chambervolume were calculated from these BLACKBEAR MONITORING IN ALASKA * Bertram and Vivion 71 measurements. they free rangedat or nearthe trapsites. We concentrated Dates when den entry occurred were recorded as the each annual trappingeffort (range: 11-13 days) in a 5 median date between the last active observationand the km2area that was accessible by boat. Annual trapping firstdenned observation. Dates when blackbears emerged areasoverlapped and were within a 13-km2area; 29 indi- from the dens where recordedas the median date of the vidual black bears were capturedand 25 were fitted with last denned observationand the first active observation. radiocollars(Table 1). We recorded25 capturesof black Bearsthat were observedout of theirden on the firstspring bearswe hadcaught previously. Two yearlingmales were telemetryflight were removedfrom the sample. Den pe- released unmarked,and 2 adult males were tattooedbut riod was the total numbersof days in the den. We used not collared. temperatureand snow course records(National Oceanic The capturesample (excluding den investigations)in- AtmosphericAdministration, Natural Resources Conser- cluded 2 yearlingmales, 3 subadultmales (mean age 2.3 vation Service, Fort Yukon, Alaska, USA) to compare years, range: 2-3), 16 adult males (mean age 8.3 years, differences between years for den entry and emergence range: 5-19), 1 subadultfemale (age 3 years), and7 adult dates. females (mean age 9.6 years, range: 4-15). Recruitmentinterval was definedas the periodbetween Annual capturerates for newly capturedblack bears productionof a litter that had successfully reachedyear- were 2.30, 0.70, and 0.44 captures/10trap days, with a ling age and productionof a subsequentlitter reaching mean of 1.26 (Table 1). Annualcapture rates for all cap- yearling age. Reproduction(interbirth) interval was the tured black bears were 3.45, 1.69, and 1.62 captures/10 periodbetween productionof a litter and productionof a trapdays with a mean of 2.35. Recapturerates increased subsequentlitter regardless of annualsurvival. annually(range: 32-73%) reflectinga high proportionof markedblack bears in the capturearea. Daily visitation StatisticalAnalyses to trapsites by black bearswas high. The meanincidence We used the nonparametricadaptive kernel procedure of black bears trippingsnares but avoiding capturewas (Home Ranger;Ursus Software,Revelstoke, British Co- 60% (range: 54-73%). No mortalitieswere associated lumbia, Canada)to estimate black bearhome ranges, se- with captureactivities. lecting the bandwidthwith least squarescross validation and using the 95% contourinterval. We chose not to use PhysicalCharacteristics the fixed kernel method because 5 black bears had <30 We recorded 2 color phases during the study: black location samples. We also calculatedminimum convex and cinnamonor brown. Four of the 29 (14%) captured polygons (Mohr1947) to estimateblack bear home ranges bearswere cinnamonphase; 3 of the 4 were female. Only to compare with previous studies (Calhome Software, 1 of 21 cubs was cinnamonphase. The incidence of cin- Fresno, California,USA). Z-tests were conductedto ex- namon phase was similarto the 11%reported from seal- amine between-yearvariation in adult survivalrates and ing recordsby the ADF&G. One black yearlingmale had differences between sex and age groups for sightability, a white chest blaze. Mean mass of subadultmales was activity patterns, and habitat preferences (Freund and 37.3 kg (range: 31.8-47.6 kg, SD = 5.2, n = 3). Mean Wilson 1997:200). Two tailed t-tests using pooled vari- mass of adult males was 87.3 kg (range: 59.1-117 kg, ances were used to analyze annual variation in home SD = 15.6, n = 16). The only subadultfemale captured ranges, den entry,emergences dates, and den period be- weighed 35.2 kg. Mean mass of adult females was 63.4 tween sex and age groups (Zar 1984:126). Black bear Table1. was determined the Capturestatistics for black bears In the western survivorship using Kaplan-Meier YukonFlats, eastern Interior Alaska, 1995-97 methodwith staggeredentry design (Pollacket al. 1989). n Because of small sample sizes, cubs were pooled for all years for survival analyses. Survival of adults was ana- Parameter 1995 1996 1997 All years lyzed by year. All groups were consideredindependent Trappingperioda 13 12 11 36 for all Trapdaysb 91 71 68 230 analyses. Snaredisturbancec 73 54 54 60 Newcaptures 21 5 3 29 Recaptures 10 6 8 24 Totalcaptures 31 12 11 54 RESULTS Newlycollared 19 4 2 25 Newcaptures/10 days 2.3 0.70 0.44 1.26 Totalcaptures/10 days 3.4 1.69 1.62 2.35 Capture a Trappingperiod = total numberdays trapped Black bears were between 24 b capturedannually May Trapdays = numberopen trapsites multipliedby and 9 June 1995-97. c trapperiod Most captures(93%) used Aldrich Snare disturbance= incidence of dislodged snareresulting in no foot snares;the remainingblack bears were dartedwhile capture 72 Ursus 13:2002

kg (range: 43.2-76.4 kg, SD = 14.3, n = 7). Twelve of 20 and54.12 cm, respectively,and included a volume of 0.16 blood samples tested positive for T gondii. m3. We did not test for differences in den morphology sows with without or with Home Habitat among cubs, cubs, yearlings Range, Use, Annual due to inadequatesample sizes. Mean annualsnow depth Movement was 58.8 cm (range: 42.7-88.9 cm, SD = 16.8, n = 24). We obtained900 locationsfrom 23 radiocollaredbears The mean time intervalused to establishden entryand between 1995 and 1997. Two individualblack bears were emergence dates between location flights was 7.6 days removedfrom the sample due to insufficientsize of loca- (range: 6-15, SD = 2.5, n = 67). Generally,bears entered tion samples. Mean annual95% contourhome rangesfor dens between 19 Septemberand 8 October(20-day span). adult females and males were 15.5 km2 and 182.5 km2, Den entrywas laterin 1997 (t = 4.1, 9 df, P = 0.002) than respectively (Table 2). The mean home range for sub- in 1995 or 1996 (Table3). We did not detect differences adult males (n = 3) was 137.6 km2. Mean annualmini- in den entry within sex or age classes. Bears emerged mum convex polygon home rangesfor adultfemales and fromtheir dens between 25 Apriland 6 May (12-dayspan). males were 9.4 km2 and 81.8 km2,respectively. Males This range of dates was more constrictedthan den entry had largerhome ranges than females (t = 2.3, 17 df, P = andwas a conservativeestimate because several bears were 0.03). already active prior to our first spring location flights. We observed 33% of all located bears on radio reloca- Mean den emergencefor all bears was differentbetween tionflights. Visualrelocation rates of subadultswere lower 1996 and 1997 (t = 3.7, 27 df, P = 0.001). Den emer- than adults (Z = -2.64, P = 0.004), and visual location gence also differed between adult males and subadult rates of females were lower than males (Z = 1.68, P < males in 1996, but sample size of subadultmales was low 0.05). Visual location ratesof adultfemales withoutcubs (n = 3). Mean length of denning was 220 days (range: and adultfemales with cubs did not differ (Z = 0.13, P = 213-229, SD = 4, n = 31). Mean den periods were con- 0.55). sistentbetween years for all sex andage groupscombined, but significantinter-year differences were noted for adult Den Ecology males (t = 2.3, 22 df, P = 0.03). We examined25 adultfemale dens in Marchand April between 1996 and 2001. Twenty-fourdens were exca- Reproduction vated on well drainedterrain in forested areas. Of these, Seven adult females were monitoredfor reproductive 10 were excavatedat the base of toppledor leaning trees; statusbetween 1996 and2001. Den visits to females with the remaining14 were excavatedfrom open areasbetween litters occurredbetween 3 Marchand 1 April. The mean live trees. One den was excavatedin an alderstand which breedingage of adultfemales in our samplewas 15 years was poorly drained. All dens were situatedon flat terrain (range: 9-21, n = 15). Five females produced 10 litters, with a slope of 0? and elevation of approximately275 m. which were comprisedof 2 single cubs, 5 sets of twins, The mean aspect for den openings was 133? (range: 0- and 3 sets of triplets(x = 2.1). The sex ratiofor newborn 270?, SD = 98.5, n = 25) and was evenly distributedbe- cubs was 14 males:7 females. The mean weight for 2 tween all quadrants. We did not have adequatesample yearlings was 15 kg. Ages and weights for parous fe- sizes to test for differencesin den aspect. All den cham- males rangedfrom 9 to 21 years, and 64 to 82 kg, respec- bers includeda cuppednest of plant materialabout 8 cm tively. We establishedage at first reproductionfor only thick. Most den entranceshad twigs, leaves, and woody one female (age 9). One adultfemale gave birthto cubs debris aroundthe perimeter,and the holes were plugged during3 consecutive years; after losing the first 2 litters with crystalizedsnow and ice. Mean height, width, and she successfully raised the thirdlitter to one year of age. length of den chamberswere 59.9, 93.2, and 137.8 cm, The recruitmentand reproduction intervals were 2.0 years = respectively, and included a volume of 0.82 m3. Mean (n = 2), and 1.6 years (n 5), respectively. height,width, and length of den entranceswere 36.0,44.0,

Table 2. Adaptive kernal home range (km2)estimates in the western Yukon Flats, eastern interiorAlaska, 1995-97 Home range Locations Group Meana SD n Range Mean SD n Range Adult 147.4 52.3 19 3.3-753.2 38 11 716 22-57 Males 182.5 245.9 15 9.2-753.2 37 10 548 22-55 Females 15.5 17.8 4 3.3-41.9 42 13 168 32-57 Subadult 106.4 107.5 4 12.9-261.2 46 2 184 43-48 Males 137.6 107.2 3 70-261.2 45 2 136 4347 Females 21.2 0 1 12.9 48 - 48 a Mean representsindividual bears across years. BLACKBEAR MONITORING IN ALASKA * Bertramand Vivion 73

Table3. Denningchronology among sex and age in the westernYukon Flats, eastern interior Alaska, 1995-97. Den entry datesa Den emergence datesb Den period (days) Group Mean SD n Range Mean SD n Range Mean SD n Range All years 26 Sepc 5 39 19 Sep-8Oct 02 Mayd 4 31 25 Apr-6May 220 4 31 213-229 Males 25 Sep 5 27 19 Sep-8Oct 02 May 4 24 25 Apr-6May 221 3 24 213-229 Adult 27 Sep 5 20 19 Sep-8Oct 03 May 4 19 25 Apr-6May 220 3 19 213-223 Subadult 19 Sep 6 7 19 Sep-8Oct 02 May 4 5 29 Apr-6May 223 4 5 220-229 Females 27 Sep 6 12 21 Sep-8Oct 03 May 4 7 26 Apr-6May 219 5 7 213-226 Adult 27 Sep 7 7 21 Sep-8Oct 02 May 4 5 26 Apr-6May 219 6 5 213-226 Subadult 26 Sep 4 2 21 Sep-8Oct 29 Apr 1 2 29 Apr 219 2 2 217-220 a Median of last active observationand first denned observation. b Median of last denned observationand first active observation. c Entrancedates were significantlydifferent between 1997-98 and both 1995-96 and 1996-97. d Emergencedates were significantlydifferent between 1995-96 and 1996-97.

Cub mass ranged from 0.6 to 2.6 kg with the lightest We did not estimate black bear densities in the study recordedweight on 6 Marchand the heaviest weight on 1 area,but we suspect,based on high capturerates and low April. hunting pressure, that densities are within the range of Bears were observedin breedingcondition between 24 densities previously reported in Alaska (86-265/1,000 May to 9 Juneduring the captureperiod and on telemetry km2;Hechtel 1991, Schwartzand Franzmann 1991, Miller flights 12 and 14 June 1995 to 1997. One adult female 1994). was capturedannually in estrus,as noted by vulval swell- Similarto other studies across NorthAmerica (Novick ing. Anothernewly capturedfemale was observed con- and Stewart 1982, Youngand Ruff 1982, Meddletonand sorting with a markedmale at a trap site. In addition,5 Litvaitis 1990, Hechtel 1991, Hirsch et al. 1999), we re- markedblack bears were observed with membersof the cordedthe largestmean minimumconvex polygon home opposite sex on 5 separate occasions during telemetry rangesin adultmales. Ourmean estimatefor adultmales flights. We did not observe any breeding behavior be- (81.8 km2,SD = 61, n = 15) was, however, considerably yond 14 June. less than the minimumconvex polygon ranges observed in other Alaska studies (151-358.7 km2). Likewise, the Survival mean home range for adult females (9.4 km2,SD = 14, n The survivalrate estimatefor cubs weaned to one year = 4) was outsidethe rangeof estimatespreviously reported was 0.45 (95% CI = 0.33, n = 20). Mortalitysources for in other Alaska studies (21 km2, Schwartz et al. 1983; cubs were largely unknown, but we did document in- 67.1 km2,adult and subadult,Miller 1987; 72.1 km2,adult stances of suspected grizzly bear predationon 2 denned and subadultHechtel 1991). female black bears with cubs. Den sites were commonly situated 100-300 m from Among adults through June 1998, we documented wetlandsin matureand well draineddeciduous and coni- mortality only among males. Two adult males died of fer forests. These sites were situatedon relatively high unknowncauses, 1 of which was observedbeing eaten by ground and elevated 1-2 m above the nearest wetland, an adultblack bear. Anothermale was killed by a grizzly which presumablyaided in preventingthe den fromflood- bear and anotherwas harvestedby a hunter. The mean ing. With one exception, bears avoided denning in bog annual survivalrate for adult males was 0.86 (95% CI = habitats,an areasusceptible to floodingduring spring thaw. 0.25, n = 15). The mean annualsurvival rate in 1997 was Previous studies in Alaska and Canadarelated den site lower than 1995 (Z = 1.97, P = 0.02). selection to topographyand climatic conditions. Black bearsin PrinceWilliam Sound and the SusitnaRiver Ba- sin used naturalden sites, whichincluded rock piles, caves, DISCUSSION and trees (Schwartzet al. 1986). Black bears that occu- Black bear capturerates in the westernYukon Flats are pied heavily forestedlowlands with relativelyflat terrain the among highest reported. Our mean capturerate (2.3 typically excavated den sites and insulated the den cup bears/10 trap nights) was higher than those reportedon with plant materials(Tietje and Ruff 1980, Schwartzet the Kenai Peninsulain Alaska (Schwartzand Franzmann al. 1986, Smith et al. 1994). Given the heavily forested 1991), Idaho (Beecham and Rohlman 1994), Louisiana areasof the YukonFlats, the lack of suitableden trees,the andMexico (Beausoleil 1999), (Doan-Criderand Hellgren prolongedperiods of temperaturesreaching -59?C during Our 1996). short annual captureperiods (11-13 days), the den period, and low average snowfall, it was not sur- have inflated however, may capturerates for comparison prising that all dens we investigated were newly exca- to other areas. vated and lined with grasses and sedges. i

74 Ursus 13:2002

Den morphology was similar to previous studies at gence dates and den periods between years, there were northernlatitudes (Tietje and Ruff 1980, Schwartzet al. only 3 days separatingthe annualmeans. Althoughlarger 1986, Smithet al. 1994;Table 4). Generally,den entrances samplesizes wouldbolster confidence in ourdata, we infer werejust largeenough to allow black bearsinto dens, and from low standarddeviations for entry,emergence, and chambersprovided minimal space for black bearsto shift den period dates that age and sex classes of bears acted position. Small den chambers,which restrictmovement similarlyin denningentry and emergence. This behavior and preventexcessive heat loss, are likely an adaptation is consistentwith weatherin northernlatitudes where the to cold climates (Tietjeand Ruff 1980). Vegetationmate- onset of spring and winter can occur in a shortperiod of rial in the den nest is common in northernareas with lay- time. ers reportedup to 30 cm (Smith et al. 1994). Reynolds et Reproductiveparameters were within the ranges re- al. (1976) reportedsimilar thicknesses for grizzly bearsin ported by Garshelis (1994) for North American studies the BrooksRange in northeasternAlaska. It was interest- and were similarto other studies in Alaska (Miller 1987, ing thatwe did not observe nesting materialthickness >8 Schwartzand Franzmann1991). We were largelyunsuc- cm despite the high availabilityof nesting materialssur- cessful at retainingcollars on yearling and subadultfe- roundingdens. males to determineage at first reproduction. However, Smith et al. (1994) summarizedentrance, emergence, an unexpected observationoccurred in 2001 when a 9- andtotal time in the den for bearpopulations across North year old female gave birthto her first litter (single cub). America and suggested thatenvironmental factors likely She had been monitoredannually in the den since the age contributeto lengthening den periods across latitudinal of 3 and had shown no previous signs of lactationor giv- andelevation gradients. Studies conducted in Alaskasup- ing birth. portthis reasoningwith the longest den periodson record, There is well documenteddata on adult and subadult which can be attributedto long winters and elevation black bear mortalitycaused by humans and food short- changes (Schwartzet al. 1986, Smith et al. 1994; Table ages, but as LeCount (1987) pointed out, limited infor- 4). Our study area is very near the northernboundary of mationexists on naturalmortality sources such as disease, suitable black bear habitatin North America, so it was cannibalism,and predation, and data on cub mortalityare not surprisingthat our mean den period (220 days) sur- rare. Determiningsources of cub mortalityis problem- to passed all other studies conductedto date. However,our atic because it is difficult to attach radiotransmitters of one longest den period for a 3-year old subadultmale (229 cubs. Our survivalrates for young to the age year Garshelis days)did not approachsome of the records(245-247 days) (0.45) were among the lowest summarizedby reportedby Schwartzet al. (1986) from the SusitnaRiver (1994) in populationsacross the continent. Conversely, Basin (62?N), which is approximately400 km south of the annualsurvival rate for adultmales was high at 0.86. a functionof both our study area and situatedin mountainousterrain at el- Alt (1984) foundthat cub mortalitywas of evations up to 2,300 m (Miller 1987). den selection and environmentalconditions; flooding We detectedlittle variationin annualweather data and natal dens contributed5.2% of cub mortalityin Pennsyl- no correlationto the late mean den entryin 1997 (3 Oct). vania. Others have attributedhigh cub mortalityto the first-time Relocation flight schedules were comparablein timing smaller size and poorercondition of producers for between years andlikely did not contributeto the late den or their lack of experience in caring young (Elowe et al. LeCount entry observed in 1997. This late date may be artificial and Dodge 1989, McLaughlin 1994). cubs = died due to inadequatesample size and high variation(n = 8; 6 (1987) found that 88% of radiocollared (n 8) of this 50% died from cannibalism, days). Although we identified differences in den emer- from predation; total, Table4. Denningchronology for blackbears InAlaska in areas of decreasinglatitude. Unk = unknown. Den entry dates Den emergence dates Den period (days) Region Reference (latitude;elevation) Mean SD n Range Mean SD n Range Mean SD n Range 4 31 213-229 This YukonFlats 26 Sep 5 42 19 Sep-8 02 May 4 31 25Apr- 220 study 6 (66?;275 m) Oct May easternInterior TananaFlats 01 Oct 9 41 19 Sep- 21 Apr 6 26 1-26 205 10 20 187-217 Smith 1994 (64?;185m) 19 Oct Apr et al. Interior SusitnaRiver Basin 09 Oct unk 116 09 Sep-8 06 May unk 116 08Apr- 218 15 116 maximum Schwartzet 1986 (62?;2,300m) Nov 23 May 247 al. south-central KenaiPeninsula 18Oct 3 164 21 Sep- 19 Apr unk 164 29 Mar- 196 13 164 not Schwartzet 1986 (60?;90m) 11 Nov 09 May reported al. south-central BLACKBEAR MONITORING IN ALASKA Bertram and Vivion 75 presumablyby adult male bears. Clark (1991) hypoth- ing these periods, but the similar mannerin which both esized that cannibalismwas responsiblefor low cub sur- dens were excavatedleads us to believe grizzly bearspre- vival in Arkansas(31%) due to the skewed male:female datedboth den sites, likely nearblack bear den emergence. ratio, which increased the likelihood of encounters be- Grizzlybear predation was also documentedon a 16-year tween adultmales and cubs. He surmisedthat adult male old male in late August 2000. The site was adjacentto bears will kill cubs priorto or duringthe breedingseason the study area in the foothills of the White Mountainsat to enhance breeding opportunity. Lindzey et al. (1986) an elevation of approximately300 m. The area was se- documentedcannibalism of 2 subadultmales and 2 den- verely disturbed,indicating an intense struggle had oc- ning adult females with cubs in a high density Washing- curred,and the black bearis skin had been invertedwith ton population with low annual cub survival (27%). most of the carcass consumed. Miller (1990) estimated Schwartz and Franzmann(1991) reportedthat an adult mean den emergencedates of 23 April (range: 5 AprilnS male killed and consumed an adult female and possibly May) for male grizzly bearand 6 May (range: 8 Aprilfi23 her 2 cubs; anotherinstance involved cannibalism of a May 23) for black bears in southcentralAlaska. We sus- yearlingmale. pect thatadult male grizzly bearmean emergence dates in We do not suspectthat dens in ourstudy area commonly our study area also precedes that of black bears. A flood prior to den emergence based on den emergence radiocollaredadult cow moose (Alces alces) was killed dates (range: 26 April to 6 May) and regional flooding by a grizzly bear in the study area between Ifi17 April patterns(late May). Because the mean breeding age of 1998. Observationsof grizzly bearor remainsof prey are adult females in our sample was 15 years, it is unlikely documentedannually by researchersand local residents thatlack of maternalcare contributedsignificantly to cub in or near the study area. A recently completed moose mortality.Although we did not documentcannibalism in calf mortalitystudy documented39% of collared moose our study,the high proportionof males in our sample and calves were killed by grizzly bears, second only to preda- one case of an adult female giving birth 3 consecutive tion by blackbears (M. Bertram,unpublished data). Griz- years leads us to believe cannibalismlikely contributed zly beardensities have not been adequatelystudied in the to low cub survival. Yukon Flats but are suspected to be approximately10/ Instancesof inter-specificpredation on black bears by 1,000 km2,which is in the low rangeof densities reported grizzly bears and wolves (Canis lupus) has been previ- by Miller et al. (1997) for Alaska. Despite low estimated ously summarizedby Smith and Follmann (1993) and densities,grizzly bearpredation was commonin the study Boyd and Heger (2000). Data pertainingto predationon areaamong all sex and age groupsof black bear. Because black bear at the den site are rare. Schwartz and moose and black bear are the 2 largest sources of food Franzmann(1991) documenteda radiocollaredcub con- mass for grizzly bear emergingfrom the den, we suspect sumed by a brownbear. Ross et al. (1988) and Smith and that grizzly bear predationon black bears is uncommon Follmann(1993) documentedpredation on dennedfemale in our study area. black bearsin the fall. We report2 instancesof probable grizzly bearpredation on dennedfemale black bearswith cubs in the spring, which are, to our knowledge, the first ACKNOWLEDGMENTS such recordings. Between 3 March and 8 July 1999, a We thank J. Akaran, F. Deines, P. Grissom, H. 15-yearold adultfemale (weight = 66 kg in March 1999) Hefferan, T. Heuer,P. Lovely, P. Martin,F. Roberts,D. and 2 neonate cubs were excavated and consumed, pre- Sowards,and P. Williams with the U.S. Fish andWildlife sumably by a grizzly bear. A second instance occurred Service, W. Hobgood with the Bureauof Land Manage- between 3 April and 25 July 2000, to a 16-yearold adult ment, and J. Hechtel with the Alaska Departmentof Fish female (weight = 60 kg in March2000) and her recently and Game (ADF&G)for assistancewith this project. We = markedfemale yearling (weight 15 kg). In both cases appreciateP. Solomon, Jr.isgenerosity in allowing us ac- the den sites had been completely excavated and the re- cess through his land to the study area. T. Beck, J. maininghole was approximately1 m wide, 3 m in length, Beecham, and J. Rohlman were instrumentalin our se- and 2 m deep. The terrainsurrounding both areas was lection of trappingmethods and design. A special thanks highly disturbedwith crushed and broken saplings, up- to D. Young(formerly with U.S. Geological Service, Bio- rooted vegetation, and exposed earth, suggesting a vio- logical Resources Division, currentlywith ADF&G) for lent struggle. The recovered collars were moderately teaching us the trappingskills to safely catch bears. The chewed, and bone fragmentsand black bearhair and hide manuscriptwas improvedby the commentsof C. Schwartz were scatteredat the den sites. We cannot confirm the and an anonymousreviewer. This researchfollowed safe deathdates precisely due to irregularlocation flights dur- animal handlingprotocol in accordancewith acceptable 76 Ursus 13:2002

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