The Effects of Developments and Primary Roads on Grizzly Bear Habitat Use in Yellowstone National Park, Wyoming

Aerial locations of radio-instrumented grizzly bears (Ursus arctos) were used to analyze effects of human activity associated with developments and primary roads on grizzly bear habitat use in Yellowstone National Park. Grizzly bear occupancy of habitat near human facilities was reduced, efficient foraging strategies were disrupted, and cohorts tending to be subordinate or security-conscious were displaced into habitat nearer developments by more dominant cohorts, particularly during summer and fall. Adult females and subadult males residing closer to developments were management-trapped at a higher rate than animals of the same class residing farther away. Adult females and subadults bore a disproportionate part of costs associated with avoiding roads and developments. For this reason and because adult females are generally thought to operate under considerable energetic duress in the Yellowstone area, avoidance of developments and roads may have resulted in higher mortality and lower productivity among the adult female cohort. Int. Conf. Bear Res. and Manage. 7:259-273 Grizzly bear populations have typically been reduced or eliminated after sustained contact with Western civilizations. This has primarily been a result of human-caused mortalities; habitat loss has been a secondary factor (Storer and Trevis 1955, Brown 1985). Therefore, management and research have been concerned with defining how much mortality and habitat loss a bear population can tolerate and remain viable. Key questions have been (1) how do bears respond to humans, and (2) how does a given response influence risk for, and habitat use by, grizzly bears? The consequences of bear-human encounters to humans have been described and analyzed (e.g., Herrero 1976, Merrill 1978, Chester 1980, Herrero 1985, Jope 1985). Other research has attempted to determine encounter effects on bears as a function of individual bear history, site, and season (Schleyer et al. 1984, Haroldson and Mattson 1985). Still other studies have investigated more general impacts of human activities, primarily in association with logging and hydrocarbon exploration and development (Elgmork 1978, Harding and Nagy 1980, Schallenberger 1980, Zager 1980, Aune et al. 1984, McLellan and Mace 1985). The effect of human activities on bears is an important issue in Yellowstone National Park; iost human activities are concentrated at roads and developments. More than 2 million people visit the park each year during the period that grizzly bears are active. Fifty percent of the park is within 8 km of a primary road and within 11.5 km of a village or frontcountry campground. Furthermore, the Yellowstone grizzly bear population appears to be marginally viable (Knight and Eberhardt 1984, 1985). Therefore, the Interagency Grizzly Bear Study Team (IGBST) used existing data to analyze the effects of roads and human developments on grizzly bear habitat use in Yellowstone Park. Our objectives were to (1) determine if observed levels of bear use were equal to that expected along roads and around developments; (2) determine if productivity of habitat occupied by bears was equal to that expected with nonselective use along roads and around developments; (3) quantify any evident avoidance by bears of roads and developments and; (4) determine if representation of different sex and age bear classes differed between areas close to and more remote from human facilities.