Inter-sexual differences in contributions of helpers in a tropical population of the cooperatively breeding Grey-crowned Babbler Pomatostomus temporalis

The Grey-crowned Babbler Pomatostomus temporalis is a group-living, cooperatively breeding species in which offspring of both sexes are equally philopatric, but only male helpers inherit the natal territory. We quantified helping efforts in a tropical population of the babbler, and tested the hypothesis that inter-sexual differences in helping efforts are related to the chance of inheriting their natal territory. We found that the total nest visiting rate during the nestling period and fledging success were higher among larger groups, but dominant birds (breeders) did not decrease their effort with group size. The total nest visiting rate during the nestling period increased with the number of female helpers, and fledging success was higher in groups with a female-biased sex ratio. In contradiction of the above hypothesis, female helpers contributed more towards nestling care than male helpers, although the latter contributed more towards nest building. There was no tendency for helpers to contribute more care towards nestlings of related breeders than those of unrelated breeders, suggesting that indirect (kin selection) benefits for helpers may be less important than direct benefits in explaining helping behaviour in this population. Our study suggests there may be sex-specific differences in the costs and benefits of helping behaviour.