Male and Female Helpers of Grey-Crowned Babblers Pomatostomus temporalis rubecula Acquire Breeding Positions in Different Ways, and don't Avoid Incest

Abstract We studied the pattern of acquisition of breeding positions among helpers in a population of Grey-crowned Babblers Pomatostomus temporalis rubecula in the monsoon tropics of northwestern Australia, using both behavioural and molecular data. In particular, we focused on sex differences, kinship, and their interactions among emigrating helpers. Moreover, we also considered whether intergroup movement and extra-pair mating contributed to incest avoidance in our population. The advantage of this material is that there are previous studies of populations in different regions, and the comparison of the results may provide a better understanding of ecological factors driving helping behaviour in cooperative breeding. Three options for a mature helper to acquire a breeding position were observed: establishing a new territory, emigrating to an existing territory, or waiting in the natal territory for a breeding vacancy. In many cases, male helpers took the third option, while female helpers took the second one. Our population of Grey-crowned Babblers seemed not to be actively avoiding incest. Female helpers tended to disperse from natal groups more than males, but neither intergroup movements nor extra-pair mating were effective in avoiding incestuous breeding. In some groups, dominant breeders were closely related to each other. The frequency of extra-pair mating in our population was similar to that of the New South Wales population previously studied, but dispersal distances were twice as great. The two populations also differ in mean clutch size and group size. Such variation in life history characteristics among different populations of cooperatively breeding species has received little attention, but has the potential to explain how cooperative breeding systems are modified by environmental factors.