Spatial-Organization of the Cooperatively Breeding Bell Miner Manorina melanophrys

Abstract

Bell Miners Manorina melanophrys are cooperative breeders and occur in discrete colonies. A colony comprised a number of breeding pairs occupying slightly overlapping foraging ranges that they shared with non-breeding offspring and immigrants. All nests belonging to a breeding pair were built within the pair's combined foraging ranges. Males remained in the natal colony until they gained a breeding position, whereas females generally dispersed to another colony. The area of an individual's foraging range did not vary significantly with its age, sex or breeding status. Helpers regularly travelled outside their foraging ranges to provision young belonging to a range of different breeding pairs. The individuals helping one breeding pair were not a mutually exclusiveset of individuals from those helping other breeding pairs within a colony. As such the social organisation of the Bell Miner does not fit within current classifications of breeding systems, but closely resembles that of the Noisy Miner M. rnelanocephala. Bell Miners exhibited extreme interspecific territoriality that resulted in almost total exclusion of all other avian species from the colony's territory. Males performed more acts of interspecific aggression than females. The extreme degree of exclusion achieved by Bell Miners may represent a benefit only attainable through cooperative group-defence of a resource.