The relationship between seasonal movements and the development of geographic variation in the Australian Chats, (Epthianura Gould and Ashbyia North (Passeres: Muscicapidae, Malurinae))

Abstract

The present paper reviews the taxonomy of the Australian chats (Epthianura Gould and Ashbyia North) and demonstrates the close link between the occurrence of geographic variation in a species and aspects of its ecology, in particular the occurrence and extent of seasonal movements. The various species differ as follows: E. crocea. - No seasonal movements, habitat specialized, distribution peripheral, and isolated in four widely separated river valleys. Marked geographic variation. A. 1ovensis. - Negligible seasonal movements, habitat specialized, range continuous but very restricted. No geographic variation. E. albifrons. - Somewhat nomadic over much of range, habitat generalized, distribution peripheral and inland. Isolated insular population (Tasmania) is the only one to have differentiated. E. aurifrons. - Seasonal movements moderate but varying with area and nature of season, habitat fairly generalized, wide and continuous interior distribution. No geographic variation. E. tricolor. - Markedly nomadic, and with seasonal shift in abundance from the south to the north of the continent. The habitat is generalized and the range interior and continuous. Breeding habits must tend to further accelerate gene flow. No geographic variation. The ultimate influence of ecology on variation in the Australian chats is best seen from a comparison of the two "extreme" species, E. crocea and E. tricolor. In the former, a series of traits combine to produce a number of distinctive isolates, forms with the "potential" of developing into new species. In the latter, by contrast, the whole behavioural pattern is such as to make the development and maintenance of any geographic variation virtually impossible.