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In order to survive and grow, neonates need to remain homeothermic. However, in the arctic, which is mostly regarded as a harsh environment with prevailing low ambient temperatures, achievement of homeothermy for chicks might cause problems. The small neonates have, besides an unfavorable volume area ratio, a less well developed plumage than adult birds. Therefore one might hypothesize that if no special cold adaptations have evolved, total energy expenditure of free living chicks is dominated by the costs of thermoregulation. Many physiologists working in extreme environments have focused on the ability of chicks to cope with low environmental temperatures (e. g. Maher, 1964; Norton, 1973; Aulie and Steen, 1976; Boggs et al., 1977; Pedersen and Steen, 1979; Bech et al., 1984; Jorgensen and Blix, 1985; Taylor, 1985; Boersma, 1986). However, to evaluate the importance of any adaptation to cold one needs to measure the actual contribution of thermoregulatory expenses to the total requirements of free living chicks. So far precise quantifications of the thermoregulatory costs in free living chicks in polar environments are only available for arctic tern chicks (Sterna paradisaea), studied on Spitsbergen (79 °N, 12 °W; Klaassen et al., 1989a,b), which are summarized here, after an analysis of possible metabolic adaptations in chicks to climatic conditions in general. |
