Relationships between activity patterns and foraging strategies of Yellowstone grizzly bears

Abstract

Eleven grizzly bears (Ursus arctos horribilis) were radiotracked in Yellowstone National Park and vicinity in 1981 and 1982. Principal objectives of the study were 1: to examine the daily and seasonal activity patterns of Yellowstone grizzlies and to determine what influence certain temporal and environmental factors had on these activity patterns and 2: to examine the interrelationships of food habits, habitat use, movements, and activity patterns. Two methods for rating the quality of a bear’s occupied habitat were employed. One method considered the abundance, diversity, and relative value to grizzlies of the vegetation occurring at field-checked relocation sites. The second method utilized existing habitat maps and a spatial information computer package to identify the habitats surrounding relocation points. These habitat types were then rated according to a system of Habitat Importance Values developed by the Interagency Grizzly Bear Study. Theoretical aspects of grizzly bear foraging strategies and predatory habits were also considered. Environmental factors which had a significant effect on grizzly bear activity patterns were temperature, precipitation, and cloud cover. Some of the influence of environmental variables on bear activity could be explained according to their probable effect on olfactory perception. Temporal factors found to be important were season and time of day (diel period). Grizzlies in this study were primarily crepuscular and nocturnal but individual bears differed significantly in their activity patterns. Individual differences in grizzly bear food habits and habitat use were reflected in their characteristic activity patterns and movements. Bears which occupied vegetatively poor habitat appeared to be more reliant on "supplemental" food sources (meat or garbage) than bears in rich mesic areas. The use of trained bear dogs to retrace grizzly bear movements proved to be a valuable adjunct to traditional research tactics.