Demography of an Insular Population of Spotted Owls

Abstract

We studied the dynamics of an insular California spotted owl (Strixoccidentalis occidentalis) population in the San Bernardino Mountains of southern California, USA. We located owls at 128 sites and banded 367 individuals between 1987-1990. We captured and color banded at least 70 percent of the territorial spotted owls in the mountain range. We measured territory occupancy, social status, nesting rate, fledging rate, fecundity, territory turnover and replacement rates, and survivorship. California spotted owls in the San Bernardino Mountains had variable annual reproduction. Survival rates were the lowest yet reported for a spotted owl population. We calculated λ=0.769 using a two stage Leslie projection matrix and this value was significantly different than 1.0. In this paper we assess the effect of sample size on the estimates of vital rates of this owl population. We discuss the relevance of insular studies of spotted owl populations to the understanding of the demographics of contiguous spotted owl populations.