Sex roles during post-fledging care in birds: female Tengmalm’s Owls contribute little to food provisioning

Abstract

Post-fledging care constitutes a large proportion of the total costs of parental care in many bird species. Despite being recognized as of critical importance to the survival of the offspring and their recruitment into the breeding population, post-fledging care, including the relative contribution by male and female parents, is under-studied. In this study, we quantified food provisioning (prey deliveries) by male and female Tengmalm’s Owl (Aegolius funereus) parents to their offspring both in the nestling and the post-fledging stages, in years of differing natural prey abundance. Parents and at least one offspring in 26 families were fitted with radio-transmitters. Male parents exhibited higher delivery rates than did females throughout the late nestling and post-fledging stages, but the intersexual difference was smaller in broods that were not deserted by the female at any stage. The female deserted her mate and offspring at some stage in 63% of the broods. Overall, deserted males delivered more prey to their offspring than did non-deserted males. Delivery rates were generally higher post-fledging. Prey delivery rates differed among years, and were highest in low vole years (probably because of smaller prey items), intermediate in peak vole years, and lowest in years of vole increase. Prey delivery rates increased with increasing brood size for both sexes, but the response was stronger in females. We suggest that female Tengmalm’s Owls contribute less than males because they are in a position to decide on their level of provisioning effort first, and because of the potential for re-mating after deserting the first brood.