Patterns of Parental Provisioning by Eastern Phoebes

Abstract

We compared patterns of male and female provisioning to nestlings in first and second broods of Eastern Phoebes (Sayornis phoebe). Female Eastern Phoebes made more trips to the nest throughout the nestling cycle. Male and female feeding rates increased with nestling age in parallel until day 11 and decline slightly to day 14 (nestlings leave the nest at approx. day 17). The median total number of feeding trips per nestling did not differ between broods for either sex. We manipulated brood sizes, within the limits of naturally occurring brood sizes, and found that the per-nestling feeding rates of both sexes were unaffected. The increasing food requirements of older or larger broods caused male and female Eastern Phoebes to increase their per-nestling feeding rates in a similar pattern. Because of similarities between the sexes in size and foraging behavior, additional costs of feeding imposed by older or enlarged broods are expected to affect members of the sexes equally.