The distribution, abundance amd seasonal movements of the pied currawong, Strepera graculina (Shaw), an important bird predator of the Phasmatidae, in eastern Australia

Abstract

In summer the pied currawong, Strepera graculina, is an important predator of Phasmatidae in the Eucalyptus forests of the highlands of eastern Australia. In winter the species congregates in large non-breeding flocks around settlements on either side of the Great Dividing Range. The distribution of the winter flocks was investigated in 1964 by sending a questionnaire to 800 schools in eastern New South Wales and most of Victoria; 603 of the schools replied. Although widely distributed, the flocks were generally concentrated around mountain areas. The total winter population in the area surveyed, excluding western Victoria, was estimated to be roughly 1,000,000 birds. Recovery data for banded and plumage-dyed currawongs show that S. graculina returns to the mountains in spring, frequently over long distances, and mainly in a south-easterly, southerly, or south-westerly direction, according to the location of the winter flocks in relation to the Great Dividing Range. There is a corresponding northerly movement out of the mountains in late summer and autumn, so that the whole population shifts regularly southward and northward in spring and autumn, respectively. The abundance and mobility of S. graculina is considered in relation to the development of phasmatid outbreaks in eastern Australia, and it is concluded that there is considerable circumstantial evidence in support of the idea that outbreaks are partly the result of a "chain-reaction" process involving the progressive relaxation of predation by at least one of the principal birds, namely S. graculina.