Thermoregulation in ratites: a review
Shane K. MaloneyPhysiology, School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia. Email: shanem@cyllene.uwa.edu.au
Australian Journal of Experimental Agriculture 48(10) 1293-1301 https://doi.org/10.1071/EA08142
Submitted: 13 April 2008 Accepted: 23 June 2008 Published: 11 September 2008
Abstract
Laboratory and free-ranging studies on the emu, ostrich and kiwi show ratites to be competent homeotherms. While body temperature and basal metabolic rate are lower in ratites than other birds, all of the thermoregulatory adaptations present in other birds are well established in ratites. The thermoneutral zone has been established for the emu and kiwi, and extends to 10°C. Below that zone, homeothermy is achieved via the efficient use of insulation and elevated metabolic heat production. In the heat, emus and ostriches increase respiratory evaporative water loss and use some cutaneous water loss. Respiratory alkalosis is avoided by reducing tidal volume. In severe heat, tidal volume increases, but the emu becomes hypoxic and hypocapnic, probably by altering blood flow to the parabronchi, resulting in ventilation/perfusion inhomogeneities. Ostriches are capable of uncoupling brain temperature from arterial blood temperature, a phenomenon termed selective brain cooling. This mechanism may modulate evaporative effector responses by manipulating hypothalamic temperature, as in mammals. The implications of thermal physiology for ratite production systems include elevated metabolic costs for homeothermy at low ambient temperature. However, the emu and ostrich are well adapted to high environmental temperatures.
Acknowledgements
Most of the work described in this review was undertaken in collaboration with Professor Terry Dawson and funded by the Australian Research Council. The author thanks the anonymous referees and editor for their many suggestions that improved the manuscript.
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