The Nesting Ecology of Sympatric Scarlet Robin Petroica multicolor and Flame Robin Petroica phoenicea Populations in Open Eucalypt Forest

Abstract

This paper compares the nesting ecology of interspecifically temtorial Scarlet Robins and Flame Robins at a site in south- eastern New South Wales. Nest site competition was not apparent between the two species of robin, and competition for food was instead considered to be a more likely cause of their interspecific temtorial behaviour. The sedentary Scarlet Robin began breeding a few weeks earlier than the migratory Flame Robin but, because of high rates of nest failure and repeat laying of clutches, the two species' breeding seasons overlapped extensively. Ten per cent of Scarlet Robins' nests produced one or more young. Twenty-five per cent of Flame Robins' nests were successful. Nest failures were mostly due to predation of eggs and young, notably by snakes and birds. I suggest that high rates of predation may have affected clutch sizes and nesting habits of Australian birds, although climatic stability and year-round availability of food probably comprise the most important selective forces on Australian birds' life history traits.