Social structure and helping behaviour of the Grey-crowned Babbler Pomatostomus temporalis
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A 4-year study of cooperative breeding in the Grey-crowned Babbler Pomatostomus temporalis was conducted in the monsoon-tropics of northern Australia. Most groups comprised a single socially monogamous pair with up to seven helpers. We found no floaters. The sex ratio was almost unity for each year. Helpers included philopatric offspring, immigrating juveniles and immigrating sexually mature birds. Adults of both sexes moved frequently between groups. Pairs without helpers were unable to raise young to fledging and often divorced, suggesting that cooperative breeding was obligatory in this population. However, for groups with helpers, the group size effect was weak; there was no significant correlation between the number of fledglings and number of helpers. Breeding females exclusively contributed to incubation. Breeders contributed more to provisioning of nestlings than non-breeders. Although helpers did not enhance the total provisioning rate to nestlings, small groups should recruit helpers to maintain the group and enhance reproductive success.
KeywordsCooperative breeding Grey-crowned babbler Helper Helping Reproductive success
We are very grateful to Mr. Richard Luxton for unrestricted access to his property, Coomalie Farm. We thank K. M. Kawano, O. Mikami, Y. Takaki, H. E. Amano, M. Kinoshita, Y. Hayashi, T. Masuda, Y. Katsuno, M. Yawata, S. Tomikawa and D. Aoyama for field assistance, and D. Saito and K. M. Kawano for DNA laboratory work. We thank two anonymous reviewers for commenting on an earlier draft of the manuscript. This study was partly financially supported by Grants-in-Aid for Scientific Research from the Japanese Society for Promotion of Science to KE (Nos. 14405007 and 17255003). This study was conducted under permits from the Charles Darwin University Animal Ethics Committee, the Park and Wildlife Commission of the Northern Territory and the Australian Bird and Bat Banding Scheme.
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