Sex and breeding status affect prey composition of Harpy Eagles Harpia harpyja

Foraging behavior may show considerable variation among population classes—such as sex and breeding class—that can be consequence of the groups’ specific constraints and roles. In raptors, differential parental roles related to foraging have been the main explanation for males being smaller than females, as smaller males have been described to be more efficient foragers. During one phase of breeding, only males forage, requiring them to feed themselves, females and young. This is expected to induce changes in foraging behavior of breeders compared to non-breeders. By comparing prey taken by floaters and breeders of Harpy Eagles ( Harpia harpyja ), we describe some effects of breeding and sex on the diet. Here we show that diet traits differed between male and female floaters, and between floaters and breeders. Juvenile prey was three times more common in the diet of males than that of females. Sloths were more common prey among females than among males (53 vs. 37%). Males preyed four times more on terrestrial animals than did females, and showed a greater niche width than females (6.0 vs. 3.4). The prey of breeders was smaller than that of non-breeders (on average 3.64 vs. 4.24 kg). Non-breeders had a larger niche width than breeders. Our data provide support for the hypothesis of parental role differentiation as an explanation for reversed sexual size dimorphism in raptors.