Ecology of Australian chats (Epthianura Gould) season movements, metabolism and ecaporative water loss

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Abstract
The 4 spp. of Australian chats [E. albifrons, E. tricolor, E. aurifrons, E. crocea] differ in their utilization of arid regions. Comparisons were made between the rates of metabolism and evaporative water loss of 3 spp. at moderate and high ambient temperatures, after trapping in the field during winter and after acclimation in the laboratory to 22.degree. and 14.degree. C. When acclimated to winter temperatures the 3 spp. had similar rates of metabolism at moderate and high ambient temperatures. The rates of evaporative water loss at moderate temperatures were similar, but at temperatures above the thermoneutral zone the rates were lower in the more xeric than the more mesic species. When acclimated to summer temperatures the more xeric species had lower rates of metabolism and evaporative water loss than the more mesic species at temperatures within and above the thermoneutral zone. Variation in the rates of metabolism and evaporative water loss in field populations was greatest in the most mesic species and least in the most xeric species. Rates of metabolism and evaporative water loss were lower in all species after acclimation to 22.degree. C than after acclimation to 14.degree. C. The rates of metabolism and evaporative water loss tended to be lower than the rates predicted on the basis of body weight. In thermoregulation at high ambient temperatures the more xeric species evaporated relatively less body water in dissipating body heat than the more mesic species, apparently without a greater increase in body temperature. The ability of Australian chats to utilize semiarid and arid regions is explained by distributions and seasonal movements which complement the physiology of evaporative water loss and thermoregulation in a manner that enhances survival at high ambient temperatures.