Glacier National Park
HABITAT RELATIONSHIPS OF GRIZZLY
National Park Service Progress Report, 1972
HABITAT RELATIONSHIPS OF GRIZZLY BEARS IN GLACIER NATIONAL PARK, MONTANA
C. J. Martinka, Glacier National Park, Montana
Abstract: Habitat use and food preferences of grizzly bears (Ursus arctos) were studied in Glacier National Park fron 1967 through 1971. Park physiolography and vegetation were described. Analysis of 353 sightings showed that grizzlies frequented low elevation coniferous forest, grassland, and snowslide habitat types in spring; higher elevation coniferous forest, shrub, and alpine types in summer and early fall; lower elevation coniferous forests in late fall. Analysis of 340 scats showed that the diet was predominated by ungulates and unidentified grasses in early spring; horsetail (Equisetem app.) and cow parsnip (Heracleum lanatum) in late spring and early summer; huckleberry (Vaccineum spp.), serviceberry (Amelanchier spp.), hawthorne (Crataegus spp.) and mountain ash (Sorbus scopulina) in late summer and early fall; grasses, roots and ungulates in late fall. Columbian ground squirrel (Citellus columbianus) supplemented the diet during all seasons. Relationships between grizzlies and Park ecosystems were discussed.
Grizzly bears originally inhabited an extensive area of western North America (Storer and Trevis 1955: 12-14). Historical accounts generally characterized the grizzly as an omnivore which utilized a wide variety of habitats and food items. This evaluation has more recently been supported by studies in Canada and Alaska (Mundy 1963, Murie 1944, Murie 1961, and others). Extensive population declines in the late 1800s, precluded similar studies for most historic ranges south of Canada.
This study was conducted in Glacier National Park from 1967 through 1971 to obtain quantitative data on status, dynamics, habitat-relationships and management of the resident grizzly bear population. Results relating to population characteristics and management to protect park visitors have been reported elsewhere (Martinka 1971a, 1971b). Data and evaluations concerning habitat use and food preferences of the grizzly population are presented in this report.
The author expresses appreciation to R. Gildart and D. Shea for field assistance. Technical assistance in analyzing scats was given by K. R. Greer, Montana Fish and Game Department. Cooperation of Glacier National Park personnel in reporting grizzly bear sightings made the study possible. The report is a contribution from National Park Service Natural Science Project GLAC-N-16.
Glacier National Park includes 1583 square miles of mountainous terrain in northwestern Montana. Topography is characterized by a central axis of precipitous peaks and ridges with streams radiating from the park as headwaters of the Saskatchewan, Missouri, and Columbia River systems. Prominent geologic features include remnant glaciers, cirques, moraines and lakes. Extensive talus slopes are common east of the Continental Divide. Elevations vary from 3,100 to 10,500 feet.
Park climate is classified as continental with Pacific maritime modifications on western slopes (Dightman 1967). Weather records for Summit (5,213 feet) showed a mean annual precipitation of 38.29 inches from 1937-66; about 60 percent fell as snow from November through April. Annual snowfall of 251 inches frequently resulted in accumulations exceeding 60 inches. Mean monthly temperature was 35.9F with extremes 15.3F (January) and 59.9F (July). Records of measurements at other elevations show substantial variations in precipitation and temperatures when compared to these means.
Park vegetation is predominated by extensive zones of alpine and coniferous forest communities. A discontinuous zone of grassland communities occurs in peripheral areas. Considerations of floral composition, physiographic sites, and successional status permitted identification of five major habitat types within these zones. Descriptions were aided by discussions in Habeck (1970).
Alpine: This type occurred generally above 6,000 feet. Meadow, fellfield and ledge communities were characterized by low-growing plants including varileaf cinquefoil (Potentilla diversifoila), snow willow (Salix nivalis), and sedge (Carex tolmieri). Alpine fir (Abies lasiocarpa) krummholz occupied a variety of physiographic sites within this type. Broad ecotones frequently formed with coniferous forest and snowslide types of lower elevations.
Coniferous Forest: This type occupied most sites below 6,000 feet. Climax forests were dominated by alpine fir, Engelman spruce (Picea engelmannii) and Douglas fir (Pseudotsuga menziesii). Seral forests were composed of Douglas fir, lodgepole pine (Pinus contorta) and western larch (Larix occidentalis). A variety of shrubs and herbs occurred in field strata of these types.
Snowslide: This type occurred frequently on more precipitous slopes within the coniferous forest zone. Shrubs were characteristic dominants with alder (Alnus sinuata) and willow (Salix spp.) abundant on most sites. Mountain maple (Acer glabrum), mountain ash and serviceberry were common in drier situations.
Shrub: This type commonly occupied sites within the coniferous forest zone for variable periods following wildfire. Willow, western serviceberry, mountain maple, redstem ceanothus (Ceanothus sanguineus) were dominant on drier sitess. Huckleberry and smooth memziesia (Menziesia ferruginea) characterized higher elevations.
Grasslands: This type occurred on alluvial fans, colluvial slopes, windblown ridges, or as a seral community following wildfire in dry coniferous forest types. Rough fescue (Festuca scabrella), bluebunch fescue (F. idahoensis), bluebunch wheatgrass (Agropyron spicatum) and sedges (Carex spp.) were characteristic dominants. Bluegresses (Poa spp.) and timothy (Phleum pratense) dominated moist depressions as well as occasional meadows. A number of minor seral types was also present, but not generally utilized by grizzlies.
Data on habitat use were obtained from sightings of grizzlies by the author, park personnel, and other qualified observers. Bears were observed while traveling park trails on foot or horseback, from a vehicle along roads, or during aerial flights. Date, location, numbers, descriptions, habitat type and elevation were recorded for each sighting. Descriptions included size, color and distinguishing features and were used to exclude possible duplicate sightings within 30-day periods. Each sighting was considered as a unit irregardless of number or group composition.
Seasonal food habits were studied from analyses of grizzly scats. These were collected along roads and trails as opportunity permitted. The presence of tracks or diggings, a minimum diameter of two inches, or both, were used as criteria to distinguish grizzly from black bear scats. Each scat was placed in a plastic bag, identified by number, and frozen upon return from the field. Laboratory analysis for food content was facilitated by emersion in water and separation in a pan. The percentage of individual food items or categories present was visually estimated. Frequency of occurrence and means of the aggregated volumes were computed for each season.
Scat analyses were complemented by evaluation of sites where grizzlies had recently secured food by digging. Habitat type was recorded for each site and food items determined from excavation characteristics. Diggings for herbaceous items were relatively shallow and showed evidence of bitten or chewed roots. In contrast, diggings for rodents commonly exposed portions of burrow systems.
Use of Habitat Types
Analysis of 353 sightings revealed that each of the major habitat types in Glacier National Park was utilized by grizzlies (Table 1). Trends which occurred in seasonal use corresponded, in general, with shifts in the altitudinal distribution of bears (Table 2). These data, when considered with sighting locations, reflected the general distribution of grizzlies throughout the park.
Table 1. Seasonal use of the different habitats by grizzly bears in >Glacier National Park as determined from 353 sightings, 1967 through 1971.
Table 2. Seasonal altitudinal distribution of grizzly bears as determined from sightings in Glacier National Park, 1967 through 1971. Sample sizes as shown in Table 1.
Spring: Grizzlies were most frequently observed on lowland habitats. Coniferous forests were the most important type with maximum use occurring along stream bottoms or in the vicinity of grasslands. Extensive tracts of upland forests were utilized less frequently. Snowslide and grassland types were used to a greater extent during spring then in other seasons. Occurrence of grizzlies in shrub types was most often recorded at low elevations.
Summer: A segment of the grizzly population moved to higher elevation habitats. Increased use of the alpine type coincided with decreased use of other types, particularly snowslide and grassland. Alpine meadow and krummholz communities were most important. Summer use of coniferous forests occurred at all elevations but a preference for higher elevations was indicated for the shrub type.
Fall: Grizzlies continued to frequent high elevation habitats in September but moved lower following frosts and early snows. Decreased use of alpine types correspond with greater use of shrub and snowslide types. Coniferous forests remained important but grasslands continued to be of minor significance. The relatively few observations made in late October and November suggested nearly exclusive use of the coniferous forest type.
Winter: Bears were generally inactive although occasional sightings of individual bears or tracks were recorded in December and March. Limited data suggested that denning and hibernation occurred in coniferous forests or higher elevation shrub types.
Analysis of 340 scats showed that the grizzly diet included a variety of plant and animal foods (Table 3). Records from 74 sites revealed that digging supplemented the diet with roots, bulbs and small mammals (Table 4). Relatively few foods contributed significantly to the diet during each seasonal period with the exception of Columbian ground squirrel. Trends in the seasonal use of certain foods appeared related, in part, to changes in habitat use.
Table 3. Seasonal food habits of grizzlies in Glacier National Park as determined from analyses of 340 scats collected from 1967 through 1971. Values are expressed as percentages.
Table 4. Habitat types and food items at 74 grizzly bear digging sites inspected from 1967 through 1970 in Glacier National Park.
Spring: Herbaceous foods predominated the diet. Unidentified grasses were the most important category with maximum use occurring during early spring. Decreased use of grasses during late May and June coincided with more frequent use of horsetail and cow parsnip.
Ungulates were eaten more frequently in spring than during other seasons. Greatest use was recorded in April when elk (Cervus canadensis) and deer (Odoccileus spp.) bulked 54 percent of 9 scats examined. Additional species recorded in May and June scats included moose (Alces alces) and mountain goat (Oreamnos americanus). Most of the insects recorded in spring scats were Coleoptera; a large proportion appeared to occur as incidental adjuncts to decomposition.
Summer: Herbaceous items were supplemented with fruits, roots and insects. Decreased use of grasses and horsetail coincided with more frequent use of sedges and cow parsnip as compared to spring. In turn, huckleberry and serviceberry progressively replaced herbs as fruits ripened. Roots and bulbs were common diet constituents; glacier lily (Erythronium grandiflorum) was the most important species. Insects, primarily Formicidae, provided more bulk to the diet than during spring.
Fall: Fruits occurred more frequently than herbaceous items. Huckleberry was the principle fruit eaten; serviceberry, hawthorne and mountain ash were important supplemental species. Use of fruits appeared to decline sharply in late October. Coincidently, unidentified roots, grasses and ungulates were the principle components of the few scats examined.
Results of this study showed that grizzly bears functioned as ommivores within Glacier National Park ecosystems. A primary herbivorous role was supplemented with scavenging or predation on certain mammals. These interactions resulted in occupancy of a relatively distinct niche by grizzlies.
Ungulate carrion was an important food source for grizzlies during early spring. Most use appeared to be of carcasses which were not utilized by other secondary consumers following natural winter deaths. Accidental deaths of wintering ungulates in snowslides provided an additional source which became progresively available during May and June. Spring distribution of grizzlies seemed closely related to these food sources.
Direct predation on ungulates supplemented scavenging activities of grizzlies during spring. Scat contents suggested that newborn young were occasionally killed following birth. Data for other age classes were unconclusive although one death of an adult female moose was recorded. Cole (1972) reported that grizzlies frequently preyed upon predisposed elk in Yellowstone National Park following winter conditions which extended into May.
Grizzlies and ungulates interacted within ecologically complete habitats (Cole 1971) in most areas of Glacier. Natural regulation and relative numerical stability were characteristic of these ungulate populations. Grizzlies benefited from both stress-related and accidental deaths which field observations suggested were largely independent of ungulate density. Accordingly, grizzlies did not appear to be important influents on ungulate population levels. Cole (1972) concluded that grizzly predation, scavenging, or both, was a nonessential but assisting adjunct to natural processes that regulated an elk population.
Spring distribution of grizzlies was also influenced by the location of certain herbs which were characteristically obtained from moist seres and bottomlands within the coniferous forest zone. Wet meadows containing bluegrasses were utilized more frequently for grazing than the drier bunchgrass types. Horsetail and cow parsnip were commonly found in moist seeps and bottomlands within the coniferous forest type. As snow melted, snowslides were an abundant source of cow parsnip, particularly on north and east exposures. Use of cow parsnip during early summer occurred at progressively higher elevations, but declined sharply following maturation and the availability of fruits.
Coniferous forests were an inportant source of huckleberry and other fruits. Early summer use by grizzlies occurred at all elevations but use progressed toward the higher elevations in August. High elevation were frequented until frosts, early snow, or both, reduced availability of palatable fruits. Dispersal of bears to lower elevation coniferous forests usually followed.
Wildfire was an important natural factor which affected the abundance and productivity of favored fruit producing plants, within the coniferous forest zone. Field observations showed both greater and more consistant production of huckleberries on burned sites than in mature forests. These relationships were most important at high elevations where a slow rate of secondary succession following wildfire permitted high production of huckleberries to continue for a relatively long interval. Grizzlies appeared responsive and reached densities as high as 1 per square mile on these sites during late summer. Jonkel (1971) reported similar observations for black bears (Ursus americanus).
Annual variations in spring weather apparently caused year to year fluctuations in fruit production by huckleberry. During this study, crop failures varied from local to parkwide in four of five years. Fluctuations of similar magnitude were not observed among other fruit-producing shrubs. Limited data suggested that these provided important alternative foods for grizzlies during years or in location of poor huckleberry production.
A distinct relationship occurred between grizzlies and alpine habitats during the snow-free period from July through September. Digging for foods was a characteristic foraging activity which resulted in extensive disturbance to alpine soils in many areas. Similar relationships have been described for populations in Canada (Mundy 1963) and Alaska (Murie 1944).
Black bears were sympatric with grizzlies in Glacier National Park. Maximum association occurred within forest and shrub habitat types of the coniferous forest zone. Food preferences of black bears (Tisch 1961) are similar to those of grizzlies in forest habitats but interspecific relationships were not apparent. In contrast, observations on the relatively open shrub types indicated that wide spacing occurred between the species or that black bears were not present. Barnes and Bray (1964) described dominance interactions between the species which were quite complex in Yellowstone National Park.
Important differences occurred between black and grizzly bears in the use of certain foods and habitats. Black bears were seldom seen in association with wintering ungulates or as predators on rodents. In addition, few black bears were observed on grassland or alpine habitat types. Widespread occurrence of ungulate populations as well as extensive alpine habitats possibly permitted relatively high densities of grizzlies to inhabit the park, as compared to other areas (Martinka 1971a, b). Jonkel (1971) reported that grizzlies seemed to prefer more open habitats than black bears.
Most terrestrial ecosystems within Glacier are essentially complete and intact. As an integral component, the grizzly population appears to be at habitat carrying capacity, relatively stable, and regulated by social interaction (Martinka 1971a, b). Developmental intrusions by humans have occurred but human activity and unnatural foods seemed more important than limited physical features in affecting grizzly habitat relationships. Management to reduce interactions between grizzlies and humans resulting from these factors has been implemented (Martinka 1971a). Potential responses to further human intrusions are not known.
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______. 1971b. Population Characteristics of Grizzly Bears in Glacier National Park. Symposium on Research in the National Parks. (In press).
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______. 1961. A Naturalist in Alaska. The Devin-Adair Co., New York. 302pp.
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Last Updated: 8-Apr-2013