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Brood sex ratios, female harem status and resources for nestling provisioning in the great reed warbler (Acrocephalus arundinaceus)

In English

Författare

Summary, in English

The theory of parental investment and brood sex ratio manipulation predicts that parents should invest in the more costly sex during conditions when resources are abundant. In the polygynous great reed warbler, Acrocephalus arundinaceus. females of primary harem status have more resources for nestling provisioning than secondary females, because polygynous males predominantly assist the primary female whereas the secondary female has to feed her young alone. Sons weigh significantly more than daughters, and are hence likely to be the more costly sex. In the present study, we measured the brood sex ratio when the chicks were 9 days old, i.e. the fledging sex ratio. As expected from theory, we found that female great reed warblers of primary status had a higher proportion of sons in their broods than females of lower (secondary) harem status. This pattern is in accordance with the results from two other species of marsh-nesting polygynous birds, the oriental reed warbler, Acrocephalus orientalis, and the yellow-headed blackbird Xanthocephalus xanthocephalus. As in the oriental reed warbler, we found that great reed warbler males increased their share of parental care as the proportion of sons in the brood increased. We did not find any difference in fitness of sons and daughters raised in primary and secondary nests. The occurrence of adaptive sex ratio manipulations in birds has been questioned, and it is therefore important that three studies of polygynous bird species, including our own, have demonstrated the same pattern of a male-biased offspring sex ratio in primary compared with secondary nests.

Publiceringsår

2000

Språk

Engelska

Sidor

312-318

Publikation/Tidskrift/Serie

Behavioral Ecology and Sociobiology

Volym

47

Issue

5

Dokumenttyp

Artikel i tidskrift

Förlag

Springer

Ämne

  • Biological Sciences

Status

Published

Projekt

  • Long-term study of great reed warblers

Forskningsgrupp

  • Molecular Ecology and Evolution Lab

ISBN/ISSN/Övrigt

  • ISSN: 1432-0762