Variation in Numbers of Yellow-tailed Black-Cockatoos in Central Coastal New South Wales

Abstract

Observations were made of the numbers of Yellow-tailed Black-Cockatoos Calyptorhynchus funereus in the Illawarra district of New South Wales between June 1982 and June 1985. One hundred and five observations were made during this period, containing a total of 415 birds, giving an average flock size of 4.0 birds. Flock sizes observed during the study period ranged from one to 20 birds, although much larger flocks have been recorded near the study area. A major peak in the abundance of Yellow-tailed Black-Cockatoos occurs in May-June and a minor one in October-November. Forty-four percent of all birds were seen during autumn, and 75 percent of all flocks contained 4 or fewer birds. It is suggested that the small flock sizes are due to their composition as fumily groups. The peaks in abundance can be attributed to an autumn movement of birds towards the coast during the May-June period and a possible return of birds through the district to breeding areas in October-November. An alternative explanation for the secondary peak in abundance could be the occurrence of nomadic behaviour prior to the breeding season, leading to an increased presence in the district at this time compared to the preceding and following months. Additional survey work is required in other regions before the movements of the Yellow-tailed Black-Cockatoo are accurately known or understood.