GROWTH AND ENERGETICS OF TERN CHICKS FROM TEMPERATE AND POLAR ENVIRONMENTS

I compared the energetics of Arctic Tern (Sterna paradisaea) chicks fr om Spitsbergen and The Netherlands, Common Tern (S. hirundo) chicks an d Sandwich Tern (S. sandvicensis) chicks from The Netherlands, and Ant arctic Tern (S. vittata) chicks from King George Island. Daily energy expenditure (DEE), measured using doubly-labeled water, was only sligh tly higher in the chicks from the polar environments, despite the high er levels of basal metabolisms (BMR) and higher costs for thermoregula tion. Apparently, thermoregulatory cost as part of the DEE of the chic k is only a minor item thanks to parental brooding, which may account for energy savings ranging from 40 to 80%. A simple model indicates th at the magnitude of these savings is dictated by the parental time bud get (i.e. the minimal foraging time needed to meet age-dependent energ y requirements of chick). Basal metabolic rate in chicks of the six av ailable studies increased with latitude. The differences could relate to a higher capacity to produce heat, which is necessary in polar envi ronments. The basal-metabolic-rate levels in adult terms, however, do not match this latitudinal pattern for the growing chicks. Ontogenetic studies over a longer time scale would be required to clarify these d iscrepancies in latitudinal pattern of BMR, for which a functional exp lanation is given in terms of differences in migratory biology.