DEVELOPMENT OF THERMOREGULATION IN THE PHEASANT PHASIANUS-COLCHICUS

1. The development of thermoregulatory capability was studied in chick s of the ring-necked pheasant (Phasianus colchicus L.) by means of met abolic rate and body temperature measurements. 2. Measurements were ca rried out for groups of 1, 5, 10, 15, and 30-day-old chicks, at 30, 20 , 10, and 0-degrees-C. 3. Pheasant chicks showed metabolic rate increa ses during lowering of ambient temperature as early as the first day o f life, although between the 1st and 10th day of life they were not ca pable of maintaining stable body temperature. 4. Fifteen-day-old chick s maintained normothermy within the 10-30-degrees-C range of ambient t emperatures while 30-day-old chicks thermoregulated over the entire ra nge of ambient temperatures.