© Marcel Burkhardt
Grüebler, M. U. & B. Naef-Daenzer (2010)
Brood overlap and male ornamentation in the double-brooded barn swallow.
Behav. Ecol. 21: 513–519
Brood overlap can be an optimal solution to the intra seasonal trade-off in the allocation of time between successive broods. In line with life-history theory, the extent of brood overlap should be adjusted according to the individual costs and benefits of the simultaneous investment into 2 broods. Phenotypic quality can affect these costs and benefits. In barn swallows (Hirundo rustica), male tail streamer length is a phenotypic quality trait, which is related to reproductive decisions, resulting in pairs with long-tailed males showing higher annual output than those with short-tailed males. We predict that the extent of brood overlap in barn swallows is positively associated with the male’s tail ornamentation. Using radio telemetry, we assessed the duration of post fledging care and juvenile survival and quantified brood overlap with unprecedented accuracy. Broods of pairs with highly ornamented males overlapped to a larger extent than those of pairs with short-tailed males. Brood overlap depended on the reproductive value of the previous brood and on female phenotypic quality. Clutch initiation after a short inter brood interval was associated with a great brood overlap. Short duration of post fledging care but not brood overlap reduced fledgling survival in first broods, and earlier second broods were associated with enlarged clutches. Thus, pairs with long-tailed males managed to increase clutch size and survival of the second brood by a nearly onset without incurring survival costs in the first brood. This is in line with the hypothesis that brood overlap enforces differential annual reproductive output among individuals varying in phenotypic quality.
Keywords:Hirundo rustica, inter brood interval, intra seasonal trade-off between broods, life history, optimal timing of reproduction, post fledging care.