The four bears that apparently re-established themselves in new areas or have not been recovered were released in habitats considered excellent. The one bear released in poor habitat returned at the rate of 5.3 miles per day, the highest rate recorded for all bears. At least seven bears when recovered had returned or were returning to a habitat considered less suitable than the transplant location.
|Table 8. Habitat quality of transplant sites in relation to homing of nuisance black bears transferred 30 to 42.5 miles from Crater Lake National Park.*|
Recoveries indicate a strong degree of homing for nuisance bears transferred 42.5 miles or less. Erickson and Petrides (1964) reported a home range area for males of 20 square miles and 10 square miles for females. Transfer distances of 30 miles or more were considered sufficient to remove bears from their home ranges or area of familiarity in the Crater Lake study. Yet 76 percent of these bears either returned or traveled in the direction of the original capture site. Only five percent of the bears transferred 30 miles or more traveled away from the capture site. Direction of movement was unknown for 19 percent. Limited data suggest that bears released in poor quality habitat may be more likely to return than those released in good or excellent habitats.
The manner in which bears oriented themselves and returned to their home ranges is unknown. In many instances bears had to travel considerable distances before visual contact could be made with familiar landmarks. The speed with which bears returned and sightings of probable returning bears indicate that little if any random wandering took place after release. The compass direction of transplant locations had no apparent influence on homing. Bears transferred more than once, in different directions, still were able to orient themselves correctly and return. Homing success and the mean rate of return were greater than reported elsewhere (Erickson and Petrides 1964; Sauer et al. 1969). The bold nature and habitual nuisance behavior of the Crater Lake bears combined with intensive recapture efforts are thought responsible.
In addition to indicating an acute homing ability, the quick return of the majority of transferred bears is strongly suggestive of a desire to leave an unfamiliar area occupied by other bears. Antagonistic behavior or its threat may force transplanted bears back onto their home ranges. The type of territorial behavior indicated for black bears by Jonkel and Cowan (1971), where social groups of bears tolerate each other but exclude others, supports this suggestion. Although no evidence was observed on recovered bears to indicate that physical conflict with other bears had occurred, the presence of resident bears could serve as a potential threat of aggression to transplanted bears.