Variation and speciation in the Australian Campephagidae (Passeres).

Abstract

The present paper reviews the taxononly of and discusses speciation in the Australian members of the family Campephagidae (cuckoo-shrikes and trillers), embracing the genera Pteropodocys Gould, Coracina Vieillot, Edolisoma Pucheran, and Lalage Boie. Isolates are few in number on the continent. This presumably results from most species having rather generalized habitat requirements, continuous ranges, being large and mobile, and undertaking seasonal wanderings. Four of the species extend widely through the tropical islands to the north. An archipelago area of about the same size as Australia provides an interesting contrast with the continent, there being some 35 morphologically differentiated isolates as against 7-10 on the latter. Tropical islands (with a constant supply of food all the year round ?) apparently favour the development of the sedentary way of life and isolation, just as the drier conditions of Australia favour nomadism and the maintenance of breeding continuity. The bulk of the insular forms, however, are small populations with restricted ranges, and must lack the adaptive gene pool of their continental congeners. Because of this their evolutionary future is presumably limited. Attention is drawn to an interesting comparison between two species that undertake equally extensive seasonal movements. One, Lalage sueurii, does not vary at all geographically, but the second, Coracina novaehollandiae, has marked clinal variation and two, possibly three, isolates. The reasons for this are discussed. The point is made that seasonal movements per se may not prohibit the development of geographic variation but that this depends on the nature of the movements.