Parental care in the multi-brooded black-throated blue warbler

Maximizing reproductive output often entails a trade-off between energy spent on current breeding attempts and that saved for future reproductive opportunities. For species with biparental care, energy spent on the current breeding attempt represents not only a trade-off with future breeding opportunities but also an interaction with the energetic effort of one's mate. In most songbird species, the female typically invests the most in the early stages of breeding. Consequently, the male's contribution to provisioning young may free the female from this energetically costly activity and aid her ability to attempt a second brood. We investigated parental provisioning in the Black-throated Blue Warbler (Dendroica caerulescens) to see if males and females altered their provisioning rates with respect to first and second broods. Using parental provisioning rates from 239 nests from three study sites over 6 years, we show that females provisioned young of first broods at a rate lower than that for second broods, while males' provisioning rate did not differ. Males' provisioning rate was inversely associated with that of females, with males increasing their provisioning when the number of young in a nest increased while females' provisioning decreased. Consequently, we believe our results highlight both the trade-off in energy females spend on current and future reproduction and the role of males' care in helping to maintain reproductive output through increased effort when conditions for feeding are difficult.