Ontogenetic study of thermoregulation in birds

We reviewed our ontogenetic studies of thermoregulatory capacity in avian embryos in relation to metabolic responses to egg cooling. Basic understanding of abrupt egg cooling and quasi-equilibrium state or cooling was discussed together with egg's thermal conductance and heat production. Two cooling tests, which were designed to minimize the rate of heat loss during cooling, were conducted to investigate a feeble compensatory metabolic response to cooling in precocial and altricial embryos, and models for early development of homeothermy in birds were suggested. Instantaneous heart rate (IHR) response to cooling was measured in chick embryos. The baseline of IHR rised and became oscillating. HR oscillation may be a phenomenon related to thermoregulation, which needs to be studied. (C) 2001 Elsevier Science Ltd. All rights reserved.