Thermoregulation in Neonate Mallee Fowl Leipoa ocellata

Abstract

Mallee fowl (Leipoa ocellata) chicks emerge from incubation mounds over summer when ambient temperature can range from 3 to 45 C and there is no free water available. The chicks, which weigh 110-120 g on hatching, are completely independent of their parents. Most chicks regulated body temperature at adult levels over the range of temperatures tested (3-46 C) by elevating metabolic rate up to three times above standard when exposed to cold stress and becoming hyperthermic during heat stress. The thermoneutral zone extended from 32 C to 39 C, and the standard metabolic rate was 0.813 ml O₂.g⁻¹h⁻¹, which is 56% of the predicted rate. The evaporative water loss was 85 % of the predicted value at ambient temperatures less than 36 C, and the coefficient of heat strain was only 46% of the expected value. The large body size, ability to increase metabolism in response to cold stress, and excellent insulating properties of the plumage enable neonate mallee fowl to survive the cold temperatures encountered in their habitat without parental brooding. It is suggested that the lower than expected standard metabolic rates of precocial chicks is related to their lower than adult body temperature and that this could be advantageous at times of food shortage.