Social Unit of the Alpine Accentor Prunella collaris in the Non-breeding Season

Abstract

The breeding unit of the Alpine Accentor Prunella collaris is a territorial group consisting of seven unrelated members. Within the group, cooperative polygynandry is common; females copulate with several male members and the males help to feed the chicks of the several females with whom they have copulated. Do Alpine Accentors, like typical cooperative breeders, maintain the membership of the group throughout the year? The social unit in winter and the wintering ecology were studied at Ashio in 1989-95, Yoshino in 1990-93 and Misaka-Pass in 1992-95. At each site, one or two (total of four) individuals banded at a breeding site, Mt. Norikura, wintered. They exhibited wintering site fidelity within seasons and between years. They were recorded singly or in flocks with less than ten unhanded birds. The unhanded birds were not members of their breeding group, which means that the breeding group was broken' up in winter. We also found no evidence of extended bonds between parents and their offspring in winter flocks. Flocks were less cohesive and their membership often changed day by day. Linear dominance hierarchies were observed within a flock. Individual activities were concentrated in particular areas, but they frequently associated with other conspecifics without aggression. Wintering individuals spent, on average, 78.1% and 17.3% of their total activity foraging and perching, respectively. Information at other wintering sites also shows that Alpine Accentors live in less cohesive small flocks but can readily switch from solitary living to flocking. We conclude that the breeding group and the winter flock in Alpine Accentors are independent of each other because there was no evidence that individual associations (group composition and family bonds) were maintained between breeding and, wintering sites.