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Sex ratio comparisons between nestlings and dead embryos of the Sparrowhawk Accipiter nisus
Author(s) -
Van Den Burg A. B.,
Van Diermen J.,
Müskens G. J. D. M.,
Van Rijn S.,
Zollinger R.
Publication year - 2002
Publication title -
ibis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.933
H-Index - 80
eISSN - 1474-919X
pISSN - 0019-1019
DOI - 10.1046/j.0019-1019.2001.00027.x
Subject(s) - sex ratio , biology , accipiter , offspring , zoology , demography , ecology , predation , pregnancy , genetics , population , sociology
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.