Sex ratio comparisons between nestlings and dead embryos of the Sparrowhawk Accipiter nisus |
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| Authors: | A. B. van den Burg ,J. van Diermen,G. J. D. M. Mü skens,S. van Rijn,& R. Zollinger |
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| Affiliation: | Division of Genetics, University of Nottingham, Queens Medical Centre, Nottingham NG7 2UH, UK;Bonendaal 6, 7231 GG Warnsveld, The Netherlands;Alterra, Wageningen University and Research Center, Department of Ecology and Environment, PO Box 47, 6700 AA Wageningen, The Netherlands;Institute for Inland Water Management and Waste Water Treatment RIZA, P.O. Box 17, 8200 AA Lelystad, the Netherlands;Jan van Galenstraat 24, 6512 HK Nijmegen, The Netherlands. |
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| Abstract: | Sex ratios that differ from unity have been reported for several bird species, but are poorly understood. Skewed sex ratios may originate at ovulation (primary sex ratio) or arise through differential mortality between the sexes (secondary sex ratio). To estimate the primary sex ratio from nestlings is difficult because in some nests not all the offspring can be sexed. Both when including and excluding such nests, there is a risk of overestimating the proportion of the better-surviving sex. Here we sexed dead Sparrowhawk embryos to determine whether unhatched eggs affect primary sex ratio estimates that are based on nestling data. In nests in which embryo mortality occurred, there was up to a 9% discrepancy in the primary sex ratio estimates based on nestlings alone compared to nestlings and dead embryos together. There was no evidence that these differences were based on sex-specific causes of mortality of embryos. |
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