Australian Field Ornithology 2012, 29, 169–181 Contributions to the reproductive effort in a group of plural-breeding Pied Butcherbirds Cracticus nigrogularis D.G. Gosper 39 Azure Avenue, Balnarring VIC 3926, Australia Email:
[email protected] Summary. Concurrent nesting by two females from a single social group of Pied Butcherbirds Cracticus nigrogularis is described. Young fledged from two nests in the first 2 years, but breeding failed in the following two seasons after Australian Magpies C. tibicen displaced the group from its original nest-tree. The two breeding females in the Pied Butcherbird group constructed their nests and incubated synchronously in the same tree without conflict. Only the females constructed the nest and incubated the eggs. Other group members fed the females before laying and during incubation. Females begged for food using a display resembling that of juvenile Butcherbirds. Most (and probably all) members of the group fed the nestlings and fledglings, with multiple members delivering food to the young in both nests and removing or eating faecal sacs. Immatures at the beginning of their second year, with no previous experience, performed the full range of helping tasks, including the provisioning of females from the pre-laying stage. During the nestling stage, the group fed on nectar from Silky Oaks Grevillea robusta, but did not feed this to the young. Introduction The Pied Butcherbird Cracticus nigrogularis (Artamidae) may breed co-operatively (Rowley 1976; Dow 1980; Clarke 1995). Higgins et al. (2006) considered it to be an occasional co-operative breeder, although the only detailed study to date (i.e.