Development of homeothermy in chicks of sub-Antarctic burrowing petrels
The development of homeothermy was studied in chicks of five species of sub-Antarctic burrowing petrels. Chicks of white-chinned and blue petrels were capable of maintaining body temperatures of 37° to 40°C at ambient temperatures between 5° and 30°C within one day of hatching. On average, chicks of grey petrels, great-winged petrels and Salvin’s prions attained homeothermy within five days of hatching, but some individuals exhibited well-developed homeothermy within 24 h of hatching. Chicks demonstrated a high capacity for heat production and maximum cold-induced oxygen consumptions ranged from 2,57 ml 02 g-1 h-1 in white-chinned petrel chicks to 4,94 ml 02 g-1 h-1 in the much smaller blue petrel chicks. The rapid development of homeothermy in burrowing petrel chicks is regarded as an adaptation in pelagic seabirds, in that it frees the adults both to replace energy reserves used during incubation and to forage for the chicks as soon as possible after hatching. In burrowing petrels it is reportedly facilitated by the chicks' thick down and a favourable burrow microclimate. This hypothesis was investigated by analysing cooling rates of dead chicks at wind speeds of 0,0 m s-1 and 7,5 m s-1, which simulated conditions within and outside burrows. Chicks exposed to windspeeds of 7,5 m s-1 lost heat at a rate 2,5 times greater than those not exposed to wind. However, this increase was substantially less than predicted for ‘model’ chicks and this difference is attributed to the efficiency of the chicks’ down.