Hatchling sex ratio and female mating status in the great reed warbler, Acrocephalus arundinaceus (Aves, Passeriformes): further evidence for offspring sex ratio manipulation

Offspring sex in birds is maternally determined, thus females are expected to vary brood sex ratio adaptively in response to various environmental and/or genetic conditions preferring one sex to the other sex. However, recent studies provide controversial evidence showing mixed support for adaptive sex manipulation theory. One problem may lie in the fact that only sex ratios at fledging have been used in many of these studies, ignoring post-hatching sex-biased mortality. To validate these results, some authors call for replication of previous researches. Here we examined hatchling sex ratio variation in relation to female mating status in a local population of facultatively polygynous great reed warblers Acrocephalus arundinaceus in Central Europe. In agreement with results of previous works, we found that monogamous and primary females had a higher proportion of sons in their broods than secondary females. These results provide further evidence that great reed warbler females manipulate the sex ratio of their offspring in response to their social status.