Sex ratio comparisons between nestlings and dead embryos of the Sparrowhawk Accipiter nisus

A.B. Van den Burg, J. Van Diermen, G.J.D.M. Müskens, S. van Rijn, R. Zollinger

    Research output: Contribution to journalArticleAcademicpeer-review

    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
    Original languageEnglish
    Pages (from-to)E39-E44
    JournalIbis
    Volume144
    Issue number1
    DOIs
    Publication statusPublished - 2002

    Keywords

    • seasonal-variation
    • birds
    • broods

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