Communal building of brood and roost nests by the Grey-crowned Babbler Pomatostomus temporalis

Abstract

Observations were made on the times of building, the construction and use of nests for breeding and roosting by the communally breeding Grey-crowned Babbler Pomatostomus temporalis in south-eastern Queensland.

Activities were recorded at ten nests built by groups numbering from three to nine birds. The breeding pair of a group did more work than all other members, and the breeding female's contribution exceeded the breeding male's. Among auxiliary members, older birds did more work than younger ones. With increasing group size, the breeding female's visiting rate and her percentage contribution to building tended to remain constant, while the breeding male's rate and percentage decreased linearly. With increasing group size, the overall building rate of groups decreased slightly, possibly due to lack of co-ordination in the activities of larger groups, but mainly because of decreased effort by the primary male.

Nests under construction were occasionally used as roosts; on completion, nests were used for either roosting or breeding, depending on the time of year. Nests used for breeding were afterwards used as roosts. Repeated repair of old nests caused these to become enlarged, but still of the same basic construction as new nests.

Roles in building and in feeding nestlings are compared among birds of different social status. The differential effort of the primary female is most obvious.