Patterns of Grizzly Bear Predation on Caribou in Northern Alaska

Abstract

We investigated grizzly bear (Ursus arctos) use of caribou (Rangifer tarandus) as carrion and prey in 3 areas: 2 areas were in or adjacent to the traditional calving grounds of large caribou herds, and 1 area that did not include caribou calving grounds. The western Brooks Range study area was located in the mountains and foothills near the calving grounds of the Western Arctic Caribou Herd (est. 200,000 in 1985); the Arctic National Wildlife Refuge study area was in the coastal plain and foothills of the eastern Brooks Range in the calving grounds of the Porcupine Caribou Herd (est. 150,000 in 1985); and the Canning River study area was in the mountains and foothills of the eastern Brooks Range, 80 km southwest of the calving grounds of the Porcupine Herd. Predation or scavenging was determined from direct observation, locating radio-collared bears feeding on caribou, and from blood on the muzzles of captured bears. The Canning River bear population was distant from calving grounds, showed little use of caribou, and was characterized by low population density and productivity. Caribou were used as carrion and prey by the 2 grizzly bear populations for which calving caribou were available. Bear population density and productivity were higher when caribou were available, even though patterns of caribou use by bears differed between the 2 areas. Near the calving grounds of the Western Arctic Herd, western Brooks Range grizzly bears stayed within their established seasonal home ranges and used caribou as the caribou migrated through their home ranges. In contrast, on the Porcupine Herd calving grounds, some Arctic Refuge bears left seasonal home ranges in the mountains to take advantage of the caribou on the coastal plain, staying only as long as the calving caribou were available. In addition, some bears that preyed on Porcupine Herd animals apparently traveled long distances following the path of migrating caribou to the calving grounds. No bears from the Canning River study area were observed to leave their home ranges to reach the calving grounds. The proportion of caribou that were killed by bears vs. those that were scavenged was not determined. Although most caribou killed by bears were calves, adults were also preyed upon. Grizzly bears of all sex and age classes fed on caribou.

Movements of Subadult Male Grizzly Bears, <em>Ursus arctos</em>, in the Central Canadian Arctic

“…Although we can expect a high degree of movement and population overlap among males in the central Arctic , it is possible that some of the subadult male ranges we recorded were somewhat inflated. We suspect that some bears in this study tracked the spring migration of Caribou (Rangifer tarandus), a behaviour previously suspected in northern Alaska for Barrenground Grizzlies (Reynolds and Garner 1987). At the daily and seasonal movement rates we observed for subadult males, because of their similarity to adult male daily movement rates, it would be possible for subadult males to have home range sizes typical of male adults in the region.…”

Defining the predator landscape of northeastern British Columbia.

“…Predation by both black (U. americanus) and grizzly bears on ungulate calves potentially can regulate ungulate populations at low densities (Reynolds and Garner 1987;Boertje, et al 1988;Larsen et al 1989;Ballard et al 1991;Schwarz and Franzmann 1991;Gasaway et al 1992). The use of ungulates by grizzly bears varies by season and area, and depends on ungulate density (Mattson 1997).…”

Distribution Patterns of Five Mammals in the Jomon Period, Middle Edo Period, and the Present, in the Japanese Archipelago

“…Densities less than 40 bears/1,000km 2 have been reliably estimated in the portions of interior Alaska without access to abundant salmon runs ( Figure 5.2) (Miller et al in prep.). These estimates range from 6.8/1,000km 2 on the coastal flatlands and adjacent foothills of the northeastern Brooks Range (Reynolds and Garner 1987) to 34 bears/ 1,000km 2 in Denali National Park (Dean 1987). These low density habitats represent about 84% of the brown bear's distribution in Alaska (Figure 5.2).…”