Thermogenic and Vocalization Responses to Cold in the Chicken Hatchling During Normoxia and Hypoxia Khalid Al Awam McGill University, King Saud University, and Prince Sultan Cardiac Centre, Riyadh, Saudi Arabia Florin Catana and Jacopo P. Mortola McGill University We investigated the vocalization and the thermogenic responses to cold during hypoxia in chicken hatchlings during the first postnatal day. Calls were quantified in number and sound characteristics (amplitude and frequency); the change in oxygen (O 2 ) consumption, measured by an open-flow methodology, represented thermogenesis. The cold challenge consisted of a decrease in ambient tem- perature (Ta) from 39 to 28 °C, in steps of 2 °C, or an acute exposure to 28 °C, either in normoxia or hypoxia (10% O 2 ). Hypoxia lowered thermogenesis and the critical Ta, suggesting a decrease in the set point for thermoregulation. The vocalization response to cold was rapid; did not progress with the duration or intensity of the cold stimulus; was similar in very young (8 hr old) and older (12–24 hr) hatchlings despite their differences in thermogenic capacity; and was essentially unaffected by hypoxia. We conclude that the hatchling’s vocalization in the cold follows a stereotyped pattern not related to the thermogenic regulation of body temperature. The dissociation between vocalization and thermogenesis might carry some advantage in conditions of cold and hypoxia. Keywords: birds, body temperature, oxygen consumption, thermogenesis When confronted by a cold stimulus, mammals and birds com- bine behavioral and autonomic responses aimed to reduce heat dispersion (thermolysis) and increase heat production (thermogen- esis). In the cold, behavioral means usually operate to decrease thermolysis, for example, by finding a proper shelter, by assuming a posture that reduces the body surface exposed to cold, or by grouping in a huddle. Autonomic responses are involuntary en- dogenous mechanisms under sympathetic control. They operate both to reduce thermolysis through peripheral vasoconstriction and to increase thermogenesis, as with shivering and brown fat ther- mogenesis. A behavioral reduction in heat loss is usually less costly than any form of endothermic heat production; hence, in the cold, in addition to autonomic responses, birds and mammals make extensive use of behavioral means for the control of body temper- ature (Bicego, Barros, & Branco, 2007). One may expect some degree of reciprocity between the autonomic and behavioral re- sponses to cold (Weiss & Laties, 1961; Schlader, Prange, Mick- leborough, & Stager, 2009). However, behavioral thermocontrol is often difficult to quantify, and little is known about its response to hypoxia. Hypoxia inhibits the thermogenic response to cold (Mortola & Gautier, 1995). This is a regulated response and not simply the effect of a limitation in oxygen availability. In fact, during hypoxic hypometabolism, physiological or pharmacological mechanisms are capable of raising oxygen consumption at or above the nor- moxic level (Mortola, 2004). In addition, during hypoxia, rats and other animals opt for an ambient temperature (Ta) that minimizes energy expenditure (Wood, 1991; Gordon & Fogelson, 1991; Dupre ´ & Owen, 1992) and increases heat loss (Tattersall & Mil- som, 2003; Scott, Cadena, Tattersall, & Milsom, 2008). This behavior has been interpreted as an indication that hypoxia shifts the set point for the control of body temperature downward (Mor- tola & Gautier, 1995). Newborn mammals and birds rely heavily on behavioral means for the control of their body temperature (Tb). In fact, at birth, newborns have minimal shivering capacity and only some degree of nonshivering thermogenesis, which improves with time in the postnatal period (Hey, 1969; Alexander, 1975; Blix & Steen, 1979; Szdzuy, Fong, & Mortola, 2008; Mortola, 2009). Like in the adult, in newborns, hypoxia depresses autonomic thermogenesis (Mor- tola & Gautier, 1995), but how this interacts with behavioral control has rarely been considered. Young guinea pigs in a ther- mocline during hypoxia chose a lower Ta than in normoxia; their response to cold was not investigated (Clark & Fewell, 1996). Newborn rats in the cold huddled less in hypoxia than during normoxia, in agreement with the concept of the drop in the Tb set point during hypoxia (Mortola & Feher, 1998). Whether or not vocalization can be considered a behavioral mechanism of defense against changes in environmental conditions is questionable. In fact, from experiments performed in neonatal rats during cold, it has been argued (Blumberg & Alberts, 1990) that the sound production is the unavoidable by-product of some degree of nar- rowing of the vocal folds (or laryngeal braking). This is a mech- anism that neonates of many species utilize, probably to improve the intrapulmonary distribution of airway pressure, lung expan- sion, and gas exchange (Mortola, 2001). In such a case, even though they can elicit a maternal response, these neonatal calls Khalid Al Awam, Department of Physiology, McGill University, De- partment of Physiology, King Saud University, and Prince Sultan Cardiac Centre, Riyadh, Saudi Arabia; Florin Catana and Jacopo P. Mortola, Department of Physiology, McGill University. Correspondence concerning this article should be addressed to Jacopo P. Mortola, McGill University, Department of Physiology, room 1121, 3655 Sir William Osler promenade, Montreal, Quebec, H3G 1Y6 Canada. E-mail: jacopo.mortola@mcgill.ca Behavioral Neuroscience © 2011 American Psychological Association 2011, Vol. 125, No. 1, 74 – 83 0735-7044/11/$12.00 DOI: 10.1037/a0021953 74