Breeding ecology of the Chestnut-crowned Babbler: a cooperative breeder in the desert

Cooperative breeding systems provide a rich testing ground for evolutionary theory because of the apparent paradox posed by individuals caring for the offspring of others. Such breeding systems are unusually common among Australian birds, but most species have been studied within the temperate and tropical zones. Here we provide the first detailed study of the breeding ecology of the Chestnut-crowned Babbler (Pomatostomus ruficeps), which was conducted in an arid-zone setting. Chestnut-crowned Babblers bred in groups of 2-13. Breeding occurred between late winter and early summer, 81% of 16 groups fledged offspring and 38% of groups fledged two broods. Clutch-size ranged from two to five, and one to five chicks fledged from successful nests after 21-25 days of provisioning. The size of the breeding unit had a significant effect on breeding success, with an extra chick fledged in the season for every three helpers in the group. These helper effects are among the strongest reported for pomatostomid babblers, perhaps reflecting the extreme environment in which this study was conducted. This study will form a basis for future research into the cooperative breeding system of Chestnut-crowned Babblers and aid with our understanding of variation in the breeding ecology of Australian babblers.