Hatching sex ratio and sex specific chick mortality in common terns Sterna hirundo

被引:0
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作者
Jacob González-Solís
Peter H. Becker
Helmut Wendeln
Michael Wink
机构
[1] Universitat de Barcelona,Department de Biologia Animal (Vertebrats)
[2] Institut für Vogelforschung “Vogelwarte Helgoland”,Institut für Pharmazeutische Biologie
[3] Institut für Angewandte Ökologie,undefined
[4] Universität Heidelberg,undefined
来源
Journal of Ornithology | 2005年 / 146卷
关键词
Offspring mortality; Rearing costs; Sex allocation; Sex biased progeny; Sexual size dimorphism;
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摘要
Bias in sex ratios at hatching and sex specific post hatching mortality in size dimorphic species has been frequently detected, and is usually skewed towards the production and survival of the smaller sex. Since common terns Sterna hirundo show a limited sexual size dimorphism, with males being only about 1–6% larger than females in a few measurements, we would expect to find small or no differences in production and survival of sons and daughters. To test this prediction, we carried out a 2-year observational study on sex ratio variation in common terns at hatching and on sex specific post hatching mortality. Sons and daughters hatched from eggs of similar volume. Post hatching mortality was heavily influenced by hatching sequence. In addition, we detected a sex specific mortality bias towards sons. Overall, hatching sex ratio and sex specific mortality resulted in fledging sex ratios 8% biased towards females. Thus, other reasons than body size may be influencing the costs of rearing sons. Son mortality was not homogeneous between brood sizes, but greater for two-chick broods. Since adults rearing two-chick broods were younger, lighter and bred consistently later than those rearing three-chick broods, it is suggested that lower capacity of two-chick brood parents adversely affected offspring survival of sons. Though not significantly, two-chick broods tended to be female biased at hatching, perhaps to counteract the greater male-biased nestling mortality. Thus, population bias in secondary sex ratio is not limited to strongly size dimorphic species, but species with a slight sexual size dimorphism can also show sex ratio bias through a combination of differential production and mortality of sons and daughters.
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页码:235 / 243
页数:8
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