Breeding-Season, Nesting Success and Nestling Growth in Carnabys Cockatoo, Calyptorhynchus-Funereus-Latirostris, Over 16 Years at Coomallo Creek, and a Method for Assessing the Viability of Populations in Other Areas

Abstract

The short-billed form of the white-tailed black cockatoo has been studied at Coomallo Creek for 16 years (1969-84), during which time the distribution of natlve vegetation in the district has greatly changed, and its total percentage has diminished from 67% in 1969 to 34% in 1982. At the same time the breeding population of black cockatoos in the area has fallen by one-third (to about 40 breeding pairs), but without any decrease in nesting success or in nestling 'fitness' as measured by comparing nestling weights with those of earlier years. The results of this study have been used to derwe a technique to assess the viability of populations of the white-tailed black cockatoo in other areas. This may be done by finding several nests, weighing each nestling, and measuring the length of its folded left wing, then aging it from a curve for growth of folded left wing drawn up from known-age nestlings. The weights of the nestlings are plotted against the appropriate ages, based on data from Coomallo Creek. Areas where nestlings show decreased 'fitness', as established by this method, may be in the process of losing their populations of the white-tailed black cockatoo.