Ecology of Australian Chats (Epthianura Gould): Reproduction in Aridity.

Abstract

The four species of Australian chats differentially occupy arid regions and are considered to have problems of water balance during reproduction. They breed mainly during the winter semester, when ambient temperatures and vapour pressure deficit are lower and evaporative losses of body water are reduced. During a drought breeding is depressed; but chats breed opportunistically after abundant rainfall and exploit, by nomadism, the unpredictable rainfall in semiarid and arid Australia. The breeding season of the most mesic species, Epthianura albifrons, is reduced in the more xeric regions. In arid sympatric breeding areas the more xeric species have the more extended breeding seasons. Chats are territorial only during reproduction. The male protects the receptive female and the eggs and offspring, but not environmental resources. Territorial defence involves plumage pigmentation consistent with Gloger's rule, plumage patterns, postures and ritualized fighting displays. Territoriality and territorial behaviour are reduced in the more mesic species. This is consistent with relative rates of evaporative water loss, synchrony and apparent density of nesting, water requirements and physiological adaptation to aridity. A hypothesis is presented which suggests an adaptive hormonal mechanism relating to physiological adaptation to aridity and determining the different plumages.