Social organisation and foraging ecology of the cooperatively breeding Chestnut-crowned Babbler (Pomatostomus ruficeps)

An individual's fitness is assumed to be maximised through early dispersal and independent breeding. However, offspring across a diversity of taxonomic groups delay dispersal and remain with at least one of their parents after reaching sexual maturity. Delayed dispersal and resulting family living are expected to arise when constraints exist on independent reproduction and where offspring benefit by remaining philopatric. A first step to elucidating the nature of such constraints and benefits for a given species is to have an understanding of the social organisation and habitat preferences of a species. The present study examined the social organisation, foraging preferences and characteristics of preferred foraging areas during a breeding season in the cooperatively breeding Chestnut-crowned Babbler (Pomatostomus ruficeps). During the study, groups of Babblers bred plurally in breeding units of two to 13 adults that occupied non-exclusive home-ranges averaging 38 ha, with larger groups occupying larger ranges. Babblers spent most of the day foraging, mostly on the ground, and preferred to forage within drainage zones. The preference for such zones probably arose because they offered both greater vegetative cover from aerial predators and biomasses of potential prey. These findings lead to the prediction that the availability of drainage zones within a group's range will influence offspring dispersal decisions in Chestnut-crowned Babblers at the site studied.