Ecological effects and social correlates of group living in the chestnut-crowned babbler (Pomatostomus ruficeps)

Group-living represents a widespread feature of animal social organisation, which has implications for the evolution of cooperation and other complex behaviours. Yet, the factors selecting for animal aggregations, in particular stable groups forming through offspring philopatry, remain elusive. This thesis examines possible costs and benefits of group living in an Australian cooperatively-breeding bird species, the Chestnut-crowned Babbler {Pomatostomus ruficeps). The study was conducted at the UNSW Arid Zone Research Station at Fowlers Gap, in the far-west New South Wales, Australia, from October 2007 to March 2010.1 found that ecology, mainly habitat characteristics and local predation pressure, has profound implications for babbler social organisation, as indicated by its effects on group size, space use, and behaviour, as well as patterns of dispersal within the study population. Specifically, predation risk appeared to vary with habitat-type and was associated with group behaviours consistent with adaptive risk reduction. Variation in local ecology was also a strong predictor of group ranging behaviour, was consistent with hypothesised local resource depletion, and seemed to interact with group size in determining movements of foraging groups on a daily basis. The importance of habitat features was confirmed by its effects on group home range size, which in turn, was a relevant predictor of group response to playback vocalisations simulating conspecific intrusion.