Breeding Season Quality, Age, and the Effect of Experience on the Reproductive Success of the Ural Owl (Strix uralensis)

Abstract

I studied the reproduction of female Ural Owls (Strix uralensis) in southern Finland in 1977-1986. I compared the age of first breeding and the reproductive success of experienced and inexperienced females in a situation where the birds subsisted on cycling voles. The proportion of first-time breeders varied annually between 0 and 38%. The breeding seasons were classified into poor, intermediate, and good according to vole abundance and winter quality. More females started to breed in intermediate than in poor or good years. Most first-time breeders were in their fourth year or older. The first breeding attempt was postponed most often because of poor environmental conditions. Experienced females laid earlier, but not significantly larger, clutches than inexperienced females. Seasonal decline in clutch size was steeper in experienced females than in inexperienced females. Brood size was not related to female experience. Thus, the reproductive output of females did not increase with experience.