Morphological and Ecological Divergence and Convergence in Isolated Populations of the Red-tailed Black-cockatoo

Abstract

The Red-tailed Black-Cockatoo Calyptorhynchus magnificus is essentially a Torresian species with six or seven isolated populations in the southern and central parts of the continent. Morphological relations between populations were an- alysed by univariate and multivariate statistics. Populations fall into three divisions: those in northern and north-eastern Australia consist of birds with long wings and large bills; that in the lower south-west consists of birds with short wings and large bills; those in central and remainder of southern Australia have short wings and small bills. Two distinct popuIations occur in south-western Australia: that in the lower south-west feeds arboreally on Marri Eucalyptus calophylla fruit and is large-billed and that in the upper south-west feeds terrestrially mainly on the introducted double-gee Emex australis and is small-billed. Divergence between the large-billed and small-billed populations in south-western Australia was probably made possible by an unsuitable belt of light woodland between their ranges. Similarities between some ,of the southern and central populations probably evolved convergently as they became adapted to similar sources of food. Southern and central Australia were probably invaded at least by a two-pronged movement from the north, one down the western part and the other down the inland-eastern part of the continent. The northern and north-eastern populations appear to be connected by a zone of hybridization in the Carpentarian lowlands. In Calyptorhynchus, the speciation of magnificus and funereus is considered to have preceded the splitting of lathami from magnifcus.