Ecology of Australian Chats (Epthianura Gould): Aridity, Electrolytes and Water Economy.

Abstract

The four species of Australian chats differentially occupy semiarid and arid regions where surface water commonly contains high concentrations of electrolytes, especially during the summer. The effects of variations in ambient temperature and salinity of drinking water on nutrition, water and electrolyte balances were compared between three species of chats in a split-plot, factorial design. The homeostatic responses revealed very complex interactions between thermoregulation, nutrition, and balances of electrolytes and water. All species have very low tolerance of electrolytes in the drinking water. Ingested electrolytes are not stored but are rapidly excreted in low concentrations at the expense of body water. Survival of chats in arid regions depends on a high degree of selectivity in avoiding water sources with even moderate concentrations of electrolytes. This avoidance is achieved by nomadism and seasonal movements to areas of recent rainfall, thereby increasing the access to water with low concentrations of electrolytes. The ability of the more xeric species to occupy regions of greater aridity cannot be explained by enhanced abilities to excrete electrolytes in high concentrations. The three species studied excrete electrolytes in similar, low concentrations. The more xeric species possess an advantage in water and electrolyte balances through lower evaporative losses of body water, especially at high ambient temperatures.