Energetics and Development of Temperature Regulation in Capercaillie Tetrao urogallus

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Abstract
Thermoregulatory capacities of newly hatched and developing capercaillie chicks (Tetrao urogallus) were studied. Metabolic rate and body temperature measurements were conducted at ambient temperatures ( ) between -30 and 37 C. The chicks rely primarily on behavioral thermoregulation. A sudden increase of basal heat production at the age of 4-5 days constitutes an important element in the control of stable body temperature ( ) and coincides with the gradual elevation of the body temperature and capacity to stimulate thermoregulatory heat production. Chicks 1-3 days old can more than double their metabolic rate at 15 C. There is no evidence of regulatory nonshivering thermogenesis. Consequently, the only way to increase heat production is to stimulate muscular activity either by shivering or by voluntary muscular activity. The most rapid development of thermoregulatory capacity occurs at the age of 7-11 days, which may be correlated with the synergistic maturation of neuronal thermoregulatory control elements and a functional hypothalamichypophysis axis. Since the development of insulation is only gradual during the first weeks of hatching, it plays only a secondary role in comparison with the behavioral means of seeking shelter under the female and an increased basal metabolic rate. Our results support the field observations which indicate that newly hatched capercaillie chicks can tolerate 10-15 C only a few minutes.

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