Natal dispersal of grizzly bears

We studied natal dispersal of grizzly bears (Ursus arctos), a solitary nont erritorial carnivore with a promiscuous mating system, between 1979 and 199 8. Dispersal distances for 2-year-olds did not differ between males and fem ales, but by 3 years of age, males had dispersed farther than females, and farther still by 4 years of age. Dispersal of both sexes was a gradual proc ess, occurring over 1-4 years. From the locations of death, or last annual ranges, it was estimated that 18 males dispersed 29.9 +/- 3.5 km (mean +/- SE) and 12 females dispersed 9.8 +/- 1.6 km. Eleven of these males disperse d the equivalent of at least the diameter of 1 adult male home range, where as only 3 of the females dispersed at least the diameter of 1 adult female home range. The longest dispersals recorded were 67 km for a male and 20 km for a female. Because the social system consists of numerous overlapping h ome ranges of both sexes, long dispersal distances may not be required to a void inbreeding or competition with relatives. Simple models suggest that 6 1% of the ranges of brother and sister pairs would not overlap, but the hom e range of every daughter would overlap her father's range. The home range of an estimated 19 +/- 4 (mean +/- SD) adult males, however, would overlap at least a portion of each female's range, thereby reducing the chance of a female mating with her brother or father. Understanding the dispersal beha viour of grizzly bears is essential for developing conservation strategies. Our results suggest that meta-population reserve designs must provide corr idors wide enough for male grizzly bears to live in with little risk of bei ng killed.