Relatedness and chick-feeding effort in the cooperatively breeding Arabian babbler.

Individual birds are expected to maximize their fitness by directing their chick-feeding effort only towards broods containing closely related nestlings. We tested this prediction using data from the cooperatively breeding Arabian babbler, Turdoides squamiceps. Individual chick-feeding effort, in the form of visit rates and load sizes delivered to the nest, was compared with three measures of relatedness: (1) band-sharing coefficients derived from multilocus minisatellite DNA fingerprints; (2) coefficients of relatedness based upon pedigrees inferred from observed group histories; and (3) observed information on relatedness that was available to the birds themselves. There was little effect of any of the three measures of relatedness on individual visit rates or load sizes delivered to the nest, both across individuals and within each group separately. In the majority of cases, we conclude that individual birds did not have access to sufficient information concerning their relatedness to the brood. As in certain other group-territorial cooperative breeders, Arabian babblers may best direct their effort towards relatives by simply feeding any nestlings that appear on their territory. Copyright 1999 The Association for the Study of Animal Behaviour.