Energetic Efficiency of Reproduction: the Benefits of Asynchronous Hatching for American Kestrels

Publication Type:Journal Article
Year of Publication:1994
Authors:Wiebe, KL, Bortolotti, GR
Journal:Journal of Animal Ecology
Date Published:1994
ISBN Number:00218790
Keywords:Falco, Falco sparverius, Falco tinnunculus, Falconidae
Abstract:1. The peak load and sibling rivalry hypotheses for hatching asynchrony in birds predict that the pattern of parental food provisioning should differ between synchronous and asynchronous broods. Monitoring parental effort is also an important step towards understanding the life history consequences of asynchrony. 2. In 1989-91, we used electronic event recorders at 57 nestboxes to record the number of visits American kestrels (Falco sparverius) made to experimentally synchronous and asynchronous broods during the nestling period. In another experiment, we recorded the prey provisioning by parents to broods supplemented with food. Nestlings were weighed every third day until fledging. 3. In all three years, parents made more visits to synchronous nests than to asynchronous ones. Provisioning rates did not differ between these two brood types when the nestlings were young, but differences in cumulative provisioning rates of up to 31% were apparent by age 25 d. Parents responded to supplemental food by decreasing the number of visits to the nest. 4. Despite the higher number of parental visits, the mass of synchronous broods at fledging was less than asynchronous broods in all 3 years. 5. Synchronous broods require more energy to rear than asynchronous broods with the same number of young. This is consistent with the sibling rivalry hypothesis, but not with the peak load hypothesis. The extra energetic cost of synchronous broods may be exacerbated when food is scarce.
Short Title:Journal of Animal Ecology
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