Influence of mate and nest-site fidelity on a declining, urban avian population

As urbanization reduces species’ habitats and population sizes, managers need information on whether within-population processes, such as changes in mate and nest-site fidelity and dispersal distances, may be contributing to declines. We investigated whether mate fidelity, nest-site fidelity, or breeding dispersal distance changed over time in a population of burrowing owls (Athene cunicularia), a short-lived, socially-monogamous species. During the 18-year period of the study, the population declined by 69% in urban Santa Clara County, California, USA--a region of rapid urbanization. We assessed whether these behaviors were influenced by key factors including age, breeding success in the previous year, and years with the same mate, and examined the relationship between mate and nest-site fidelity over time and annual reproductive success. To evaluate the relationship between mate and nest-site fidelity as well as overall mate and nest-site fidelity rates by sex, we used Chi-Square tests. For all other tests, we used Generalized Linear Mixed Models (GLMM) with individual bird identification as a random variable to address the inclusion of the same birds in multiple years. Our analyses showed no change over time in mate fidelity, nest-site fidelity rates, dispersal distances, or annual reproductive success, indicating these behaviors remained stable even during a severe population decline. Although burrowing owls are a short-lived species, we found that increasing years with the same mate resulted in increased mate fidelity, nest-site fidelity, and annual reproductive success. Since these fidelity behaviors were maintained during the population decline, other factors require investigation to determine the causes for decreases in numbers in this population. Thus, even species such as burrowing owls, which can maintain important fidelity behaviors in urban setting, are still subject to other pressures that can cause population declines.