COMPARATIVEECOLOGY OF BLACKAND GRIZZLY ON THE ROCKYMOUNTAIN FRONT,

KEITHE. AUNE,Montana Departmentof Fish, Wildlifeand Parks, WildlifeLaboratory, Montana State University, Bozeman, MT 59717

Abstract: Seven black bears ( americanus) were radiomonitoredduring 1981-84 in conjunction with a long-term study of grizzly bears (Ursus arctos). Grizzly and black food habits, home ranges, habitatuse, and denning habits were compared within the composite home range of all radio-instrumentedblack bears. Trapping effort per capture for each species was compared in 6 bear management units for the period 1980-87. Differences in habitatuse and denning habitatwere evident. Black bears used the forested habitats more frequently than did grizzlies. Grizzly bears utilized riparianand open habitatcomponents habitats more frequently than did black bears. Grizzly bear dens were on steeper slopes and at higher elevations than black bear dens. Subtle differences in food habits were detected. Less effort was necessary to capture black bears in bear management units with lower grizzly densities. Grizzly bears avoided habitats within 300 m of open roads while black bears avoided habitats within 100 m of open roads.

Int. Conf. Bear Res. and Manage. 9(1):365-374

Black bear and grizzly bear are sympatric in many STUDY AREA areas of . Despite the numerous bear The study area lies along the east face of the studies conducted throughout this continent few have ContinentalDivide in northwesternMontana (Fig. 1). empirically defined the niches of these 2 closely related Herrero the East species. (1978, 1979) compared Glacier .4 ? evolutionary adaptations of grizzly and black bears 2'T Medicinec N noting that of these 2 species the grizzly bear is better to more habitats. Observation adapted exploit open Heart 0 10 20 km based field studies have not provided strong empirical ~IButte evidence for the Hererro but partitioningsuggested by y-J do suggest some temporal or spacial division of habitat (Shaffer 1971, Lloyd and Fleck 1977). Black bear and grizzly bear relationshipshave been recently studied in portions of northwesternMontana (Carriles and Jonkel 1987, Kasworm and Thier 1990)...... Most of these studies have occurred in heavily forested . habitats dissimilar to the drier, more habitats ii. !iii quite open eJ of central Montana. This paper describes how black Chateau and bears habitat the grizzly partitioned along Rocky r MountainFront in northcentralMontana. The temporal / and of these 2 are $A spacial relationships species briefly :i: Augus..ta. discussed. o for this research was Montana 0 Funding provided by 1^ O Augusta Department of Fish, Wildlife and Parks (MDFWP), ',v4 Bureau of Land Management(BLM), U.S. Department of Agriculture Forest Service (USFS), U.S. Fish and Wildlife Service (USFWS), and The Nature Conservancy (TNC). I would like to acknowledge Wayne Kasworm, Tom Stivers, and Mike Madel who assisted in the data collection and analysis during the LEGEND grizzly and black bear studies v BLACKBEAR F DISTRIBUTION 1980-84. William Callaghan and Ken Greer provided services and scats. : GRIZZLYBEAR laboratory support analyzed Many DISTRIBUTION 4 talentedindividuals from the MDFWP, USFWS, USFS, TNC, and BLM provided field and administrative support during the study. Fig. 1. Map of the study area showing overlapping distributions of black and grizzly bears. 366 Int. Conf. Bear. Res. and Manage. 9(1) 1994

The northernboundary is Highway2 and the southern Capturedbears were anaesthetized with a 1:1 ratioof boundaryis Highway200. The studyarea is bounded phencyclidinehydrochloride (Sernylan) and promazine on the west by the upperportions of the SouthFork of hydrochloride(Sparine) or a 2:1 ratio of ketamine theFlathead River, and the Middle Fork of theFlathead hydrochloride(Ketaset) and xylazine (Rompun). Bears River withinthe Flathead,Lolo, and HelenaNational were markedwith numberedand colored plastic ear Forests.The eastern boundary extends to approximately tags placedin each ear. Eachbear was measuredand Range 6 West. Bureauof Land Managementlands, whenpossible weighed with a springscale. All grizzly Montana Departmentof Fish, Wildlife and Parks bearsand a selectnumber of blackbears in a portionof wildlife managementareas, national forest non- the study area from Sun River northto Birch Creek wilderness,and private lands were the primary focus of wereradioinstrumented. the research. Trappingeffort was recordeddaily and summarized Brieflydescribed, elevations on the studyarea range annuallyfrom 1980 to 1987. A trapnightwas defined from about 1,280 m (4,200 ft.) in river valleys and as 1 trapsite open for all or part of a night period. plainsto the east of the mountainsupward to 2,863 m Some trap sites had multiplesnares placed arounda (9,392 ft.) on mountaintops. Sedimentaryrocks of the bait. The study area was stratifiedinto 6 bear limestoneand dolomitetypes generallyform the peaks managementunits (BMU) for analysisof trap effort andhigh ridges,while rocks of the sandstonetype often data. underliethe valley bottoms. Alpineglaciers extensively Radio-instrumentedbears were relocated during modifiedlandforms in the past. weekly aerialflights from a Piper Supercubequipped Annual precipitationaverages about 31 cm (12 with a belly mountedYAGI antenna. Radiolocations inches)at Choteauand up to 167 cm (65 inches)near wereopportunistically obtained from the ground. Black the ContinentalDivide. Approximately80% of the and white photographswere made of each aerial precipitationfalls as snow. Temperaturesrange from relocationto assisthabitat determination and to properly 32?C (90?F) to about-46?C (-50?F). The climateis locate the site on a map. Data recordedat each characterizedby long, cool winters, short, warm location included elevation, habitat type, habitat summers,and strongsouthwest winds. component,slope, aspect,and UTM coordinates. All The majordrainage systems within the study area grizzlyand blackbear radio relocations, observations, includethe DearbornRiver, Sun River, TetonRiver, tracks, dens, kills, and depredationsrecorded from BirchCreek, and Two MedicineRiver. Manyof the 1978 to 1987 were mapped to determinespecies drainagesform a characteristictrellis patternwith distribution. at narrowcanyons joining main rivers at abruptangles. Scats were collected,frozen, and later analyzed Riparianvegetation extends into the high plains and theMDFWP laboratory to determinecontents. Grizzly providesfood andcover for blackand grizzly bears far and blackbear scats were distinguishedby monitoring frommountainous habitat. radio-collaredbears, collecting at capturesites, and with tracksor Subalpinefir (Abies lasiocarpa)is dominantand confirmingevidence at collectionsites and representsclimax on most of the timberlineforest. hair. Frequency,percent frequency,volume, scatcontents. Standsof spruce(Picea spp.), white-barkpine (Pinus percentvolume were determined from the albicaulis),lodgepole pine (Pinus contorta), Douglas-fir Each food categorywas expressedby an importance (Psuedotsugamenziesii), limber pine (Pinusflexilis), value and percentimportance using Mealey's (1980) aspen(Populus tremuloides), and cottonwood (Populus formulawhere: trichocarpa)are found on selectlocations, depending on landform,aspect, and elevation. Naturalgrasslands ImportanceValue = Percent Frequency x Percent Volume cover the plains and foothillsat lower elevationsand 100 intergradewestward into limberpine savanna. Percent importancevalue is defined by the following expression: = ImportanceValue Percent ImportanceValue of Category x 100 Sum of ImportanceValues METHODS were tested Bearswere trappedusing foot snares(Johnson and Differencesin frequencyof foods by around Pelton1980). Snareswere set in log cubbies,on trails, developingsimultaneous confidence intervals in black bear or occasionallyat dip or barrel sets. Traps were observedfrequency of food categories checkeddaily by vehicleor withsaddle horse and pack dietsfor comparisonto expectedproportions. Expected use string. proportionswere derived from the observed by COMPARATIVEECOLOGY OF BLACK AND GRIZZLY BEARS * Aune 367

grizzly bears. The hypothesistested was that black Spearmansrank correlation,regression analysis, and bearchoose food categoriesin the sameproportions as analysisof variance. grizzlybears. Dens were located by randomchance, helicopter surveysin denninghabitat, and radiotrackingbears to RESULTS their dens from the air or ground. Data gatheredat each den site includedelevation, aspect, slope, habitat Distributionand Home Range type, den type, andcondition of the den. Datesof den Distributionmaps developed from 4,138 grizzlyand emergence and den entrance were determinedby 1,226 blackbear observations illustrate the overlapping radiomonitoringbears at den sites. Differencesbetween range of black and grizzly bears on the Rocky median dates of den entranceand emergencewere MountainFront (Fig. 1). Eachspecies showed a strong testedusing Chi-squareanalysis (Zar 1984). affinityto the forestedmountain habitats near the Front Sixteenhabitat components were definedaccording Range. Blackbears were morestrictly confined to the to descriptionsdeveloped by Aune et al. (1984). forestedmountain areas and less frequentlyobserved in Availabilityof habitatcomponents and distances to road theplains regions of the studyarea. Grizzlybears were categorieswere determined using nonmapping methods more frequentlyobserved utilizing habitats well out described by Marcum and Loftsgaarden(1980). onto the plains away from the mountain front. Analysis of habitatpreference followed Nue et al. Concentrationareas were similarbetween species with (1974) and Byers et al. (1984). Habitatpreference of the exceptionof high peak areaswhere grizzly bears grizzly and black bears was comparedfor the region dug rootsin the alpine. within the total compositerange of all black bears. Blackbears were capturedin each of the 5 grizzly Habitatavailability was determinedfrom 2,276 random bear managementunits (BMU) where grizzlies were points plotted over the 1,100 square kilometer also captured,1980-86 (Fig. 2). The grizzly bear compositehome range of blackbears in the study. The capturerate was 135.5 trapnitesper captureand 184.0 perimeterof the composite polygon was used to trapnitesper individualgrizzly. Theblack bear capture generatea subsetof data from the grizzlybear radio rate averaged32.8 trapnitesper capture and 34.4 relocationrecords for comparisonsof habitatuse. trapnitesper individualbear. Captureeffort expressed Comparisonsof categoricaldata including slope, aspect, in trapnitesper bearwas lowestin the Sun RiverSouth and elevationwere testedusing a Chi-squarestatistic. BMU and highest in the Teton Birch BMU. The Mean values of slope and elevationby season and regressionof captureeffort for blackbears on grizzly betweenspecies were testedusing analysis of variance. bearsdemonstrated a negative relationship; however the Habitat use between species was compared by slope was not significant (r2 = 31.48, P = 0.33). generatingexpected values from habitat use by grizzly Convexpolygon home ranges of 7 residentblack bears bears and comparingthese to habitatuse by black monitoredbetween 1981 and 1984 overlappedwith 6 bears. residentgrizzly bear home rangeswithin the samearea The distancefrom bearlocations to open roadswas determinedby measurementson a 1:24,000 USGS Trap Nights Per Bear quadrangle.Open roadsincluded all roadsaccessible 300 - vehiclefor or by any any all seasons. Distanceto road 2 5 0 ...... datawere categorized into 5 distanceto road categories. 2 0 0 ...... Relativeavailability of habitatwithin each distanceto ...... roadcategory was determinedfrom the randompoints 15 0 generatedwithin the compositehome rangeof radio- 100 - ...... instrumentedblack bears. of 50:- Analysis variancewas L L used to meansfor distanceto road seasons 4MI 1*77A7 W 1Wf62/ M compare by 0o1r I,II - andbetween species. Badger Birch Teton S.F. Sun Dearborn Home-range analysis was conducted using the Bear Management Unit TELDAY home-rangeprogram (MDFWP). The _ Grizzly Bear m Black Bear TELDAYprogram generated a minimumpolygon home range (Mohr 1947). The statistical package Fig. 2. Comparisons of black and grizzly bear STATGRAPHICS Inc. was used for captures per (STSC, 1986) unit effort by Bear Management Units for the Rocky Mountain statistical analysis applying Chi-square, t-tests, Front, 1980-87. 368 Int. Conf. Bear. Res. and Manage. 9(1) 1994

1981-84 (Fig. 3). Unmarkedresident black and grizzly spp.) were the most common eaten by black bears were also observed within the area. Average and grizzly bears. Other large herbivores in the scats home-range size for resident grizzly bears was 1,185.6 of bears were domestic sheep (Ovis aries) and km2 (N = 2, SD = 740.4) for males and 642.3 km2 (Cervus elaphus). Insects and were present in (N = 8, SD = 265.9) for females. Residentblack bear bear diets also. The major insect eaten was ants. home ranges averaged 224.8 km2(N = 5, SD = 111.9) parts were infrequently found in scats and then most for males and 137.3 km2 (N = 2, SD = 96.2) for often during nesting season. Although observations did females. Resident grizzly bear home ranges were not confirm that grizzlies killed black bears, black bear approximately 5 times the size of resident black bear hair was found in grizzly bear scats. Grizzly bear hair home ranges. was not detected in scats of black bears. Plant parts selected from the vegetation eaten by Comparison of Black and black and grizzly bears varied with food category. Grizzly Bear Food Habits and leaf parts were the common plant parts Two hundred and seventy-six black bear and 1,094 found in shrub food species eaten by black and grizzly grizzly bear scats were analyzed to compare bear food bears. Whitebarkpine nuts were the major plant part habits. Bear scats contained food items from 11 major found for the category. Graminoidswere primarily taxonomic groups including mammals, insects, birds, composed of stem or leafy parts. The forbs in bear (pine nuts), sporophytes, forbs, roots, graminoids, diets were mostly upper plant parts including leaf, stem, shrubs (fruit), garbage, and other (debris). flowers, seeds, and fruit. Very little root matter was Graminoids, forbs, and insects were the most common detected in black bear scats. bear foods along the East Front and these foods had There were significantdifferences between species in high percent frequency values. In contrast, seasonally the frequency of use for the 8 more common food important or less common foods such as fruits, categories identified in scats (X2 = 47.6, df = 7, mammals, sporophytes, and pine nuts had low percent P < 0.05). The frequency of grass, forbs, shrubs, and frequency values. Graminoids, forbs, and fruit had the insects was high for both species (Table 1). Grizzly highest percent volume of all bear food taxon. bear scats contained roots, mammals, and pine nuts Domestic cattle (Bos taurus) and (Odocoileus more frequentlythan did black bear scats (P < 0.05). Black bear scats contained insects more frequently than did grizzly bear scats (P < 0.05). Comparison of the importance value percent by season indicatesa similar seasonal feeding strategy with subtle differences (Fig. 4). Graminoidswere important in all seasons for both species. Forbs appear to be

Table 1. Frequency, percent frequency, and percent volume of food categories found in scats from black and grizzly bears on the Rocky Mountain Front.

Grizzly bear Black bear Percent Percent Percent Percent Food category Freq. freq. volume Freq. freq. volume Tree 91 5.1 5.9 12 4.3 3.7

Shrub (Fruit) 315 28.8 18.8 69 15.4 15.4 Sporophyte 100 9.1 3.5 32 11.6 6.0 Graminoid 557 50.9 23.2 142 51.5 25.0 Forb 341 31.2 16.3 106 38.4 25.0 269 24.6 8.8 48 17.4 6.9 Insect 340 31.1 6.1 114 41.3 7.5 Root 119 10.9 7.3 3 1.1 0.9 Fig. 3. Grizzly and black bear home-range overlap on the Rocky Mountain Front, 1981-84. COMPARATIVEECOLOGY OF BLACKAND GRIZZLYBEARS * Aune 369

Table 2. Mean elevation for black and grizzly bear use by season on the Rocky Mountain Front

Blackbear Grizzlybear Mean Mean elevation elevation Season (m) 95% CI (m) 95% CI

Spring 1,653.1 1,605.4-1,653.1 1,672.3 1,641.2-1,703.6 Summer 1,714.9 1,677.8-1,751.9 1,780.9 1,742.7-1,819.1 Grizzly Black Grizzly Black Grizzly Black Spring Summer Fall Fall 1,881.3 1,821.9-1,940.8 1,807.3 1,769.9-1,844.7

_ Tree f Shrub M Sporophyteix Graminoid Forb II Root Fi Mammal 0n Insect Grizzly N-1094 Black N-276 broader spectrum of elevations and used the low and upper elevational range more frequently than black Fig. 4. Black bear and grizzly bear seasonal food habits for bears. the Rocky Mountain Front, 1980-87. Mean slope used by grizzly bears increased significantlyeach season from spring through fall while mean slope used by black bears did not increase until more important throughout the summer and fall for fall (Table 3). There was a significant difference in black bears whereas importance value of forbs percent slope categories used by black and grizzly bears decreased for grizzlies after mid summer. Grizzly (X2 = 125.8, 7 df, P < 0.05). Grizzly bears used bears dug roots during the summer and fall while black flatterslopes significantlymore and steep slopes slightly bears did not. Berries and pine nuts were importantto more often than black bears. Black bears remained on both species during the fall. Insects had higher moderately steep slopes more often than did grizzly importancevalues for black bears than for grizzly bears bears (Fig. 6). for all seasons. Grizzly bears had higher percent Comparisons of the aspects used by each species importancevalues for mammals in all seasons. indicated significant differences (X2 = 136.2, 8 df, The species of graminoids identified in grizzly and P < 0.05). Grizzly bears used flat terrain with little black bear scats were similar, with Poa spp. and discerable aspect more frequently than did black bears spp. being most important. Domestic oats (Avena (Fig. 7). Black bears used the northeast, east, and sativa) was found in scats from grizzly bears feeding in southeast slopes more than did grizzly bears. cultivated fields at low elevations. Oats were rarely Use/availability analysis indicated a difference in found in black bear scats. Forbs utilized by both habitatpreferences by these 2 species (Table 4). Black species were similar, including such moist-site species and grizzly bears preferred the closed timbered such as Angelica spp., Taraxacumspp., Lathyrusspp., Osmorhizaspp., and Heracleum lanatum. The fruits of shrub species utilized by both black and grizzly bears included Prunus virginiana, Amelanchier alnifolia, , and Arctostaphylos uva-ursi. Importance values for Arctostaphylos uva-ursi were higher for black bears than for grizzly bears. Importance values for Prunus virginiana and Amelanchier alnifolia, the common low-elevation shrubs, were higher for grizzly bears than for black bears. 1450 1850 2250 Elevation Category Midpoint (m) Comparisons of Habitat Use The mean elevation for black and grizzly bears 1 Black Bear M Grizzly Bear increased from spring to fall (Table 2). Black bears Black N-299 Grizzly N-1538 were located at sites within the mid range of elevations more frequently than grizzly bears (X2 = 268.5, 10 df, Fig. 5. Distribution of black and grizzly bear use by elevation P < 0.05) (Fig. 5). The grizzly bears ranged a categories for the Rocky Mountain Front. 370 Int. Conf. Bear. Res. and Manage. 9(1) 1994

Table 3. Mean percent slope for black and grizzly bear use by season on the Mountain Front. Rocky 50-'

Blackbear Grizzlybear Mean Mean Season slope 95% CI slope 95%CI 20 ------...... ------Spring 24.4 21.2-27.7 17.9 16.2-19.6 - Summer 24.6 21.0-28.1 21.7 19.7-23.7 20-. _a ..1 fcl a -.... Fall 36.4 31.8-40.9 27.3 25.0-29.6 N NE E SE S SW W NW Flat ASPECT component and Populus stands. Black bears Black Bear E Grizzly Bear demonstrateda preference for limber pine forests while grizzly bears did not prefer this component. Both Fig. 7. Use of various aspect categories by black and grizzly species did not prefer the prairie grasslands, meadows, bears on the Rocky Mountain Front, 1981-84. roads, and ripariancomplex. Comparisons of the habitat use between species revealed that although both prefer the closed timber on steeper slopes than were black bear dens (P < 0.05) habitat component, black bears were using the closed (Table 6). timber community more than were grizzly bears Black bears entered dens from 13 October to 30 (P < 0.05) (Table 5). Black bears used the November and emerged from dens 20 March to 5 May. rock/talus/scree, prairie grasslands, riparianshrub, and Grizzly bears entered their dens from 10 October to 5 riparian complex habitat component significantly less December and emerged from dens 10 March to 13 than did grizzly bears (P < 0.05). All other May. Median date for den entrance for black bears components were used in the same proportions as was 10 November (N = 8) which is similar to the grizzly bears. median date of 7 November (N = 45) for grizzly bears (P = 0.52). The median date for den emergence for Comparisonsof DenningHabits black bears was 4 April (N = 8) which is near the 7 Fourteen black bear dens were located within the April (N = 43) median date of emergence for grizzlies study area. Nine of these dens were examined from the (P = 0.19). ground; all were excavated. Thirty-four grizzly bear dens were located within a similar and region. Grizzly Table4. of habitat and black bear dens were located on similar Use/availability components by grizzly aspects black bears on the core area of the Rocky MountainFront. (X2 = 2.9, 2 df, P < 0.05) (Fig. 8). Grizzly bear dens were found at significantly higher elevations and Preference/Avoidancea Habitatcomponent Blackbear Grizzlybear Speciespreferring use Meadow Equal Road Equal Sidehill park 0 0 Equal Snowchute 0 0 Equal Shrubfield 0 0 Equal Rock/talus/scree 0 Grizzly Closed timber + Equal Limber pine Black Prairie grassland + Equal Mm. grassland O Black Populus stand Equal Riparian shrub 0 + Grizzly Percent Slope Ripariancomplex Equal timber 0 0 Equal 1 Black Bear 3 Grizzly Bear Open Timber shrubfield 0O 0 Equal Unknown Equal Fig. 6. The use of various slope categories by black and grizzly bears on the Rocky Mountain Front, 1981-84. a(-) equals avoidance, (+) equals preference, (0) equals proportional. COMPARATIVEECOLOGY OF BLACKAND GRIZZLYBEARS * Aune 371

Table 5. Black bear habitat use (percent) compared with Table 6. Comparisons of slope and elevation between black grizzly bear habitat use on the Rocky Mountain Front. bear dens (N = 14) and grizzly bear dens (N = 34) in a similar portion of the Rocky Mountain Front. Observed Expected Difference Habitatcomponent (black) (grizzly) (P = 0.05) Species Meanelevation 95%CI Meanslope 95%CI Meadow 0.013 0.005 0 Black 1,715.5 1,632.7-1,798.4 28.8 19.9-37.7 Sidehill park 0.017 0.005 0 Grizzly 2,166.7 2,113.6-2,219.9 56.7 51.0-62.4 Snowchute 0.010 0.008 0 Shrubfield 0.003 0.005 0 Rock/talus/scree 0.010 0.081 Closed timber 0.488 0.259 + these 2 related limber 0.027 0.030 0 space occupied by closely species. pine bears have an to the Prairie grassland 0.003 0.031 Grizzly expanded range compared Mt. grassland 0.013 0.005 0 black bears on the Rocky Mountain Front. Both Populus 0.231 0.241 0 species were closely associated with forest Riparian shrub 0.027 0.191 along the Rocky Mountain Front. However, the 0.000 0.012 Ripariancomplex forest/plainsecotone along the front provided extensions Open timber 0.120 0.103 0 Timber shrubfield 0.037 0.008 0 of cover out onto the plains, which grizzly bears Unknown 0.000 0.017 frequentlyused. Capture data from different regions of the Rocky Mountain Front indicate that there may be differences in the abundance of black bears relative to the Road Disturbance abundanceof grizzly bears. Aune and Kasworm (1989) The mean distance to all open roads for black and reported that grizzly bear densities in southern BMUs grizzly bears increased significantly for each season (P were lower than in northern units. Density estimates < 0.05) (Table 7). Mean distance to roads for all are not availablefor black bears. It did appearthat less seasons was significantly greater for grizzly bears than effort was needed to captureblack bears in BMUs with black bears (P < 0.05). Grizzly bears avoided the lower grizzly bear densities. areas within 300 m of open roads (P < 0.05) (Table Differences in the relative abundance of black and 8). Black bear were avoiding the areas within 100 m grizzly bears could result from interspecific of any open roads (P < 0.05). competition, varying human-causedmortality rates, or habitat differences. Habitat in the northern region of our study area was superiorto that in the southern area DISCUSSION for both black and grizzly bears (Aune and Kasworm Black bears and grizzly bears share a common range 1989). Black bear capturerates did not conform to this along the Rocky Mountain Front. Distributions and gradientin habitatquality as expected. Human-caused home ranges demonstrated significant overlap in the mortality rates were not known for the southern and northern portions of the study area. Superior black bear capturerates in the southern region of the Rocky Relative I MountainFront a that the observed I Frequency support hypothesis - / 60 7- - abundance of black bears could have been induced 50..- ...... I...... -......

40..- ...... I...... I...... I...... Table 7. Mean distance to open roads for black and grizzly 30..- ...... I...... I...... I ...... I... I...... bears by season on the Rocky Mountain Front.

20.- .- ...... I...... ,e Blackbear bear ...... Grizzly 10..-. ... - ,- . o/ I/ //5AI _ 5,2 _ a, Mean Mean Northeast Southeast Southwest Northwest distance distance ASPECT OF DENSITES Season (m) 95 % C.I. (m) 95 % C.I. Spring 616.3 544.0-773.8 1,434.8 I Black Bear / Grizzly Bear 1,288.3-1,581.5 Summer 982.1 787.5-1,177.2 1,917.3 1,728.0-2,106.5

Fig. 8. Comparison of aspect of black and grizzly bear dens Fall 1,692.5 1,360.0-2,025.0 2,900.2 2,640.7-3,159.8 on the Rocky Mountain Front, 1980-87. 372 Int. Conf.Bear. Res. and Manage.9(1) 1994

Table 8. Use/availability analysis for 100 meter distance species-specific adaptations, and the interspecific categories for black and grizzly bears on the Rocky Mountain between these Black bears seemed Front. competition species. to rely on forbs throughout the year more than did while bears shifted to other food Distancecategory Blackbeara Grizzlybear grizzly bears, grizzly items during the summer and fall. Grizzly bears are 0-100 more root than are black and 100-200 0 capable diggers bears, 200-300 0 exploited sidehill parks and alpine habitat to a greater 300-400 + + extent. The slightly higher portion of mammals found 400-500 0 + in the grizzly bear scats suggests that grizzly bears may + + 500+ out-compete black bears for carrion or are better a predators. Shaffer (1971) and Jonkel and Cowan (_)equals avoidance, (+) equals preference, (0) equalsproportional. (1971) reporteda higher proportionof mammals in the diets of grizzly bears when compared to black bears. by low grizzly bear densities and reduced Grizzly bears utilize a broader range of food resources interspecificcompetition. available throughout a given environment while black The minimum home-range area for female and male bears concentrateon food resources within the forest black bears in this study was considerably larger than (Herrero 1979). in other areas of Montana(Kasworm and Manley 1988, There did appear to be some niche separation Mack 1988). Adult female home-range size was between these 2 species, indicated by preference for considerably larger in this study than reported for the various habitatcomponents, differentpatterns in use of (22 km2) (Kasworm and Manley elevations, and differences in food habits. Black bears 1988) or the East Boulder (27-38 km2) (Mack 1988). were concentrating Their life activities in forested Amstrup and Beecham (1976) suggested that the habitats, which are found on north by northeast slopes quality, quantity,and distributionof food, as influenced at middle elevations and middle to low slopes. Grizzly by climate and topography, probably determinehome- bears were able to exploit a broaderrange of elevations range size. and used lower elevation ripariancomponents and the Black bear habitat on the Rocky Mountain Front is alpine environmentsseasonally. Hererro (1978, 1979) similar to habitat on the East Boulder in south-central noted thatwhile these 2 species coexisted in some forest Montanabut quite different than habitatin the Cabinet ecosystems the grizzly is better adapted for exploiting Mountains of northwesternMontana. Smaller female more open habitat. In discussing the evolution of bears home ranges in the Cabinet Mountains are best Herrero(1978) suggests that the black bear retainedthe explained by differences in habitat quality. Female forest-dwelling niche of Their ancestors while the home-range size on the Rocky MountainFront was 2-3 moved to exploit more open habitatsas well times larger than home-range size reportedfor the East as forests. The subtle differences in habitatselection on Boulder. This difference in home-rangesize may result the Rocky MountainFront support these postulates. from factors other than habitatquality. Black bears on the Rocky MountainFront may prefer One factor influencing home-range size of black the forested habitats as a form of protection from bears could be interaction between grizzly and black grizzly bears. Grizzlies have been reported to kill bears (Jonkel 1987). Field observations from several black bears (Arnold 1930, Horocker 1962, Jonkel and studies indicate that black bears are displaced from Cowan 1971, Murie 1981). Black bears are adept at in feeding areasby grizzlies (Kendall 1984, Shaffer 1971). climbing trees and may be able to escape predators Herrero In this study observationsof interspecificstrife in the forested environment (Herrero 1979). fields and near carcasses indicated that grizzly bears (1978) suggests that the black bear did not move out of was not to displaced black bears. If black bear and grizzly bear the forested habitats since it large enough from interaction is frequent, avoidance behavior and protectits young, or possibly itself, on the ground bear black displacementof black bears could result in largerhome larger carnivores. Grizzly upon ranges. Furtherstudy is needed within similar habitats bears could have important population regulation the selection of but varying densities of bears to determinethe influence implications and could prejudice of grizzly bears on black bear home-range size. habitatsby black bears. the Black bear and grizzly bear diets along the Rocky Temporalpartitioning of resourcescould mitigate Mountain Front were different. The differences were interspecificcompetition in habitatscommonly selected bears. Shaffer observed probably related to the habitatseach species preferred, by black and grizzly (1971) COMPARATIVEECOLOGY OFBLACK AND GRIZZLY BEARS * Aune 373

that when both species were in berry fields disturbances increased in the Swan Hills region of each foraged at different time periods. Jorgensen , black bear densities increased while grizzly (1979) suggested that limited overlap in peak activity bear densities declined. Increased roading of the patterns probably reduced interspecific competition relatively unroaded Rocky Mountain Front could between these 2 species. Schleyer (1983) reported displace grizzly bears and bestow a competitive differences in the time of captures between the 2 advantageto black bears. species, suggesting that the species were active during Stirling and Derocher (1990) suggest that the different periods of the day. Aune and Kasworm distribution and abundance of Ursids is but an (1989) reported crepuscular and nocturnal activity ephemeralreflection of the evolutionarypath that began patternsfor grizzly bears on the Rocky MountainFront. with the first identifiable bear. They further suggest Limited observation and activity data collected during that bears have adapted to ecological changes that this study yielded evidence of some temporal isolation affected interspecific competition and availability of in activities. Further investigationsof activity patterns food. Empiricalevidence from this study demonstrate would be necessary to determine precisely how black that black and grizzly bears on the Rocky Mountain and grizzly bears partitionedresources temporally on Front have adapted to exploit different subniches and the Rocky Mountain Front. coexist within a common habitatbecause of differences Although there was some overlap, grizzly bears and in behavior, food habits, and habitat selection. These black bears partitioneddenning habitatalong the Rocky conclusions imply that ecological or human-induced Mountain Front. Grizzly bear dens were found on change would affect the distributionand abundanceof high-elevation, steep slopes along the front range while these 2 Ursids by altering habitats or providing either black bear dens were located in a broad zone from mid- species a competitive advantage. elevation forests to the riparian areas of the prairie. Both species chose aspects that collect snow cover during the winter. Overlap of grizzly and black bear LITERATURECITED habitat be more denning may prevalentin other areas of AMSTRUP,S.C., ANDJ. BEECHAM.1976. Activity patterns where grizzly bears were known to of radio-collaredblack bears in . J. Wildl.Manage. den at lower elevations (Aune and Kasworm 1989). 40:340-348. On the Rocky Mountain Front frequent chinook ARNOLD,B. 1930. Cannibalbear. YellowstoneNat. Notes winds during the winter can melt snow cover on 7(8):54. at lower denning slopes especially elevations. Grizzly AUNE,K.E., ANDW.F. KASWORM.1989. Final report-east bears claim den may sites at high elevations with more front grizzly studies. Mont. Dep. of Fish, Wildl. and consistent snow cover while black bears, to avoid Parks.Helena, Mont. 332pp. select the mid-lower grizzlies, may slopes. Partitioning _ , T. STIVERS,AND M. MADEL. 1984. Rocky mountain habitat on the denning Rocky Mountain Front may front grizzly bear monitoringand investigation. Mont. black bears from provide protection grizzly bears Dep. Fish, Wildl. and Parks.Helena, Mont. 239pp. during the pre- and post-hibernationlethargy. There BYERS, C.R., R.K. STEINHORST,AND P.R. KRAUSMAN. be a selective for both may advantage species by 1984. Clarificationof a technique for analysis of habitat on partitioning denning the Rocky Mountain utilization-availabilitydata. J. Wildl. Manage.48:1050- Front. 1053. Black bears on the Mountain Front Rocky exploited CARRILES,H., ANDC.J. JONKEL.1987. Black bear/grizzly habitat nearer to roads more open readily than did bearcompetition for space. Proc. 1985Predator Symp. 3. grizzly bears. Kasworm and Manley (1990) also In Press. observed differences in displacement zones for black HERRERO,S. 1978. A comparisonof some featuresof and grizzly bears in the CabinetMountains of Montana. evolution, ecology, and behavior of black and grizzly Lloyd and Fleck (1977) reportedthat grizzly bears are bears. Carnivore1:7-17. avoiding areas humans whereas frequented by black 1979. Black bears: the grizzly's replacement? bears are not. Black bears apparentlytolerate human Pages 179-195 in D. Burk, ed. The black bear in modern disturbanceto a than do greater degree grizzly bears. North America. Proc. Workshop on Manage. Biol. of The black bear's to disturbed habitats ability exploit North Am. Black Bear, 17-19 Feb. 1088. Kalispell, Mont. a survival to may provide advantage this species in Booneand Crockett Club and Camp Fire Club of America. roaded habitats. and heavily Nagy Russell (1978) HORNOCKER,M.G. 1962. Population characteristics and suggested that as human encroachment and habitat social and reproductive behavior of the grizzly bear in 374 Int. Conf.Bear. Res. and Manage.9(1) 1994

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