Gender-specific dispersal distances of grizzly bears estimated by genetic analysis

Natal dispersal is difficult to quantify, and long-distance events are often undetected, leading to biased estimates. Following offspring from their natal home range to their postdispersal adult breeding home range is challenging, and gathering sufficient data for large mammals with long generation times is particularly difficult. Here we measure average sex-specific dispersal distances in grizzly bears (Ursus arctos L., 1758) using individual-based genetic analysis. We genetically sampled and generated 15-locus microsatellite genotypes for 711 grizzly bears over a range of 1 00 000 km 2 in southwestern Canada. Microsatellite markers are inherited in a Mendelian fashion, allowing us to use likelihood-based parentage analyses to estimate parent-offspring dyads. We used the distance between individually captured females of parent-offspring pairs (i.e., mother-daughter) to estimate female natal dispersal distances and found that, on average, females dispersed 14.3 km from the center of their natal home range. We used the distance between males of parent-offspring pairs (i.e., father-son) to estimate average male dispersal distances and found that males dispersed, on average, 41.9 km from their natal, or maternal, home range (mother-son dispersal distance). We used a simulation model to estimate the bias associated with measuring the father-son (male-male) distance as an estimate of the mother-son distance.