Natal dispersal of the spotted owl in southern California: Dispersal profile of an insular population

We studied the dispersal patterns of an insular population of California Spotted Owls (Strix occidentalis occidentalis) in southern California from 1987-1998. The study area encompassed the entire San Bernardino Mountains and included a nested, 535-km² study area which we used to evaluate the effects of study area size on dispersal parameter estimation. One hundred and twenty-nine of the 478 banded juvenile owls (27%) had entered the territorial population by 1998. Over half of the successful dispersers became territorial within one year. Additionally, all females and 95% of the males occupied territories within three years. Twenty-three sibling pairs and one set of triplets dispersed successfully. Sibling dispersal distances were not correlated. Sixty-seven males and 62 females dispersed 2.3-36.4 km (mean ± SD = 10.1 ± 7.6 km) and 0.4-35.7 km (mean ± SD = 11.7 ± 8.1 km), respectively. The difference between male and female mean dispersal distances was not significant. Dispersal distance and first-year survival were underestimated when using data collected within the smaller, nested study area. The presence of conspecifics may play a key role in the settling process. Seventy-eight percent of the dispersers settled in territories that were occupied by either pairs or single owls the previous year, 16% settled in vacant territories next to occupied sites, and 6% settled at sites of unknown occupancy. No owls settled at unoccupied sites that were not adjacent to occupied sites.