RESTING AND PEAK METABOLIC RATES OF ARCTIC TERN NESTLINGS AND THEIR RELATIONS TO GROWTH-RATE

We measured resting and peak metabolism in relation to growth rate in arctic tern Sterna paradisaea chicks over the first 10 d after hatching. For chicks with varying growth rate, body mass seems to be a better predictor of resting metabolic rate than age. The effect of changes in growth rate on resting metabolism of arctic terns is smaller than that found interspecifically in hatchlings. It is possible that differences exist in the heat increment of feeding between fast and slow growers that would further reduce the effect of growth rate on resting metabolism. Chicks that had body masses lower than 75% of that expected for their age were metabolically inferior in withstanding a thermal challenge compared with chicks of the same age but of normal mass. In contrast to resting metabolic rate, the extent of peak metabolic rate is related to both body mass and age. Thus, in part, the maturation of the thermoregulatory system proceeds steadily with time even when body mass lags behind.