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. Dispersión Natal de Strix occidentalis occidentalis: Descripción de la Dispersión de una Población Insular Resumen. Estudiamos los patrones de dispersión de una población insular de lechuza moteada californiana (Strix occidentalis occidentalis) en el sur de California, desde 1987–1998. El área de estudio comprendió las montañas de San Bernardino e incluyó un sito de estudio de 535 km2 incluído en esta zona el cual usamos para evaluar el efecto del tamaño del área de estudio para la estimación de los parámetros de dispersión. Hasta 1998, 129 de las 478 lechuzas juveniles marcadas (27%) habían entrado a la población territorial. Más la mitad de los dispersores exitosos se hicieron territoriales al cabo de un año. Adicionalmente, todas las hembras y el 95% de los machos ocuparon territorios al cabo de tres años. Veintitrés pares de hermanos y un triplete se dispersaron exitosamente. La distancia de dispersión entre hermanos no se correlacionó. Sesenta y siete machos y 62 hembras se dispe