DEVELOPMENT OF TEMPERATURE REGULATION IN SHOREBIRDS

We studied the influence of body size on the development of temperatur e regulation in chicks of 10 North American and five European shorebir d species belonging to the families Charadriidae and Scolopacidae. Neo natal body mass ranged between 4 and 55 g, and asymptotic body mass ra nged between 20 and 650 g, We measured the change in body temperature of chicks individually exposed for 30 min to ambient temperatures of 2 -degrees, 10-degrees, and 18-degrees-C. An index of homeothermy for ea ch species at each ambient temperature increased as a linear function of the logarithm of body mass. Before achieving homeothermy at 18-degr ees-C, chicks of small species almost tripled their body mass from hat ching whereas chicks of the largest species increased their body mass by only 10%. In the five European species we studied the development o f resting and peak metabolic rate, and minimal thermal conductance, as a function of body mass. The development of homeothermy resulted main ly from a strong increase in the maximum mass-specific heat production due to thermogenesis (peak metabolic rate minus resting metabolic rat e in the thermoneutral zone). The latter phenomenon is linked with a p arallel reduction of the relative growth rate of the chick. These resu lts are consistent with the hypothesis of Ricklefs (1979), who suggest ed that well-developed muscle function is incompatible with a high rel ative growth rate.