Mathematical Demography of Spotted Owls in the Pacific Northwest

Abstract

We examined the mathematical demography of northern spotted owls (Strix occidentalis caurina) using simple deterministic population models. Our goals were to gain insights into the life history strategy, to determine demographic attributes most affecting changes in population size, and to provide guidelines for effective management of spotted owl populations. The spotted owl apparently has evolved high adult survival rates associated with irregular and unpredictable reproduction. The finite rate of population change (.lambda.) in this subspecies is most sensitive to variation in adult survival rate and relatively insensitive to variation in fecundity and age at first reproduction. However, rates of population change are strongly affected by reproductive senescence if it occurs before 15 years of age. Sound management practices should include efforts to control factors that adversely affect the survival rate of adult females.