Behavior of grizzly bears (Ursus arctos) toward people was studied by examining hikers' reports of grizzly bear observations and by intensively observing grizzlies in an area of Glacier National Park that was heavily used by day-hikers. Of concern were the apparent
habituation of grizzly bears to people in the study area, the increasing rate of human injuries by grizzly bears in the park, and the increased involvement of lone adult and subadult bears in injuries to hikers. Associations between environmental circumstances,
including the presence and behavior of people, and grizzly bears' behavior were evaluated. Human use of the study area was associated primarily with season and weather. Numbers of grizzly bears observed were also associated with season as it reflected patterns of habitat use. Behavior of grizzly bears was associated primarily with the level of human activity, the presence of bear-bells, and the climatic circumstances under which the bears were seen. Although grizzly bears' fear response toward people appeared to habituate, they maintained a degree of vigilance that was related to conditions affecting the ease of scent perception. Charges, which have been associated with hiker injuries, involved only people who did not have bearbells. Charges occurred primarily along trails that received little human use although grizzly bears were also startled by hikers on trails with high levels of human use. Evidence indicated that habituation of grizzly bears' fear response did not lead to the increasing trend in the rate of human injuries. On the contrary, habituation may contribute to a reduction in the rate of injuries that result from fear-induced aggression. A possible mechanism for the increased rate of injuries is presented. Other types of aggression relevant to danger of human injury by grizzly bears are discussed.