Hybridization and migration in Australian populations of the little and rufous-breasted bronze-cuckoos

Abstract

Principal component analyses of variation in coloration of the Little Bronze-Cuckoo Chrysococcyx malayanus minutillus and Rufous-breasted Bronze-Cuckoo C. russatus show that these forms intergrade completely and that intermediates occur throughout northern and north-eastern Queensland. Their similar ecology and behaviour combined with significant similarities in morphology, such as coloration of eye-ring of males, and songs, probably facilitate hybridization. The form C.m. barnardi of south-eastern Queensland and north-eastem New South Wales is apparently only slightly affected by russatus genes, is longer winged than minutillus. of north-western Australia from the Kimberley to the Gulf of Carpentaria and migrates north in winter to Cape York Peninsula and southern New Guinea. There is no real evidence for migration in russatus and minutillus Multi-discriminant analysis shows that minutillus-like individuals from the islands of the Banda Sea are more like C.m. rufomerus, the endemic form of the islands, than minutillus; some specimens are apparently intermediate in coloration between rufomerus and minutillus. These minutillus-like individuals appear not to be migrants from north-western Australia. Hybridization between different forms in secondary contact may be common in the C. malayanus complex; for, C.m. salvadorii of Babar Island is intermediate in coloration between C.m. rufomerus of the Banda Sea islands and the distinctive C.m. crassirostris of the Moluccas, and the long-winged population in southern New Guinea may be affected by gene-flow from the more widely distributed C.m. poecilurus of New Guinea. The pattern of variation in this complex in Australia suggests two separate invasions, the first via north-western Australia giving rise to minutillus and barnardi and the second from New Guinea producing the hybrid population on Cape York Peninsula and in north-eastern Queensland.