ORIGINAL PAPER Shane K. Maloney Æ Graeme Moss Æ Tammy Cartmell Duncan Mitchell Alteration in diel activity patterns as a thermoregulatory strategy in black wildebeest (Connochaetes gnou) Received: 19 April 2005 / Revised: 16 June 2005 / Accepted: 26 June 2005 / Published online: 28 July 2005 Ó Springer-Verlag 2005 Abstract The nychthemeral activity patterns of a popu- lation of female black wildebeest inhabiting a shadeless environment were surveyed periodically over 1 year. The wildebeest fed mostly at night, with the proportion of feeding at night increasing when ambient conditions were hotter. Inactive periods were spent mostly lying during cooler weather but standing as days became hotter. We suggest that the entire suite of behavioural adjustments is beneficial to heat exchange with the environment. Behaviour patterns were markedly different during one warm weather survey, from the other warm weather surveys, when an 8-month dry spell had just been broken. We suggest that this may reflect the availability of water for autonomic thermoregulation, a consequent decreased reliance on behavioural thermoregulation, and a release of the thermal constraints on foraging. Our results help to explain the ability of black wildebeest to maintain body core temperature within a very narrow range despite being exposed to an environment with large ny- chthemeral variations in thermal conditions and offering little in the way of microclimate selection. Keywords Behaviour Æ Black wildebeest Æ Diel activity patterns Æ Thermoregulation Æ Ungulates Æ Connochaetes gnou Introduction Autonomic temperature regulation, defined as the involuntary thermoeffector response to heat and cold including sweating, tachypnea, shivering and non-shiv- ering thermogenesis, and adjustments in circulatory convection to the body surface (Mercer 2001), incurs costs to a homeotherm in terms of energy for enhanced heat production or water for evaporative cooling. Complementary to autonomic thermoregulation is behavioural thermoregulation, generally considered the ‘‘cheap option’’, which involves either avoidance of ambient extremes (microclimate utilisation) or postural adjustment altering energy exchange with the environ- ment. Inhibiting behavioural responses to a thermal challenge increases the energetic cost of homeothermy (McEwen and Heath 1973) and may lead to altered body temperature patterns (Fuller et al. 1999). Optimisation of the response to thermal stress should implement the least-costly behavioural responses before autonomic shivering or sweating/panting (Satinoff 1996). While there has been considerable enquiry into operant re- sponses to thermal stimuli in the laboratory (see Caba- nac 1996; Satinoff 1996), our knowledge of the extent to which behaviour is used as a thermoregulatory effector in free-ranging homeotherms, and especially large mammals, is scant. In the opinion of some, behavioural thermoregulation, beyond shade seeking and bathing, does not play a role in large animals (Davenport 1985). Laboratory-based operant conditioning studies have revealed that the control of behavioural responses to thermal stimuli is similar to that of autonomic re- sponses. There is a threshold body (hypothalamic or skin) temperature for initiation of a conditioned re- sponse and an increase in intensity as body temperature deviates further. There is also evidence that these oper- ant responses can be modified if conflicting demands are made on a behavioural common path, such as when food or water are withheld from an animal placed in the S. K. Maloney Æ T. Cartmell Æ D. Mitchell School of Physiology, University of the Witwatersrand Medical School, Johannesburg, 2193 South Africa G. Moss Department for Environment and Heritage, Kangaroo Island, SA, Australia S. K. Maloney (&) Department of Physiology, Biomedical and Chemical Science, University of Western Australia, 35 Stirling Highway, Crawley, 6009 Australia E-mail: shanem@cyllene.uwa.edu.au Fax: +61-8-64881025 J Comp Physiol A (2005) 191: 1055–1064 DOI 10.1007/s00359-005-0030-4