Huddle-roosting behaviour of the Varied Sittella Daphoenositta chrysoptera in relation to social status

Abstract

The Varied Sittella Daphoenositta chrysoptera is a small communally-breeding passerine. Throughout the year, the members of a group roost together, huddling alongside each other on a dead branch, facing the same way. In one marked group of five to seven birds, the two oldest males were usually the first to arrive at the roost-sites, and always occupied the end positions of the huddle. The breeding female was usually third to arrive, but her position in the huddle, as with the remaining group members, changed unpredictably during the period of study. The outermost male, which had the least restricted view, stayed awake longer than the other group members, suggesting a guard role. The juveniles were the first to go to sleep, possibly due to lack of responsibility. The ritualised submissive behaviour of the non-breeding male towards the breeding male, and aggressive interactions between other group members, when arriving at the roost indicate that the roost-site is an important place for reinforcing, and perhaps even establishing, dominance relations. Although predation and social cohesion undoubtedly influence the roosting behaviour of this species, the primary function of huddling is probably energy conservation.