GROWTH AND ENERGETICS OF ARCTIC TERN CHICKS (STERNA-PARADISAEA)

Abstract

--We studied energy requirements of Arctic Tern chicks (Sterna paradisaea) in Ny ,idesund, Svalbard (79oN, 12oW) with special emphasis on thermoregulatory andactivity costs. We used doubly labeled water to estimate energy expenditure in the field (Ea•w) and made laboratory measurements ofthe different components of total energy requirement Comparison of DLW-estimates with oxygen consumption measurements howed that underestimated total energy expenditure 4.5-16.0% depending on the duration of the experiment. This was probably due to incorporation of isotopes in newly synthesized tissue. Field estimates of total energy expenditure from Ea• • were corrected accordingly. A tern chick model was used to measure operative temperature (T,). At midday T, reached values up to 20oC above ambient emperature (Ta) which ranged from 3.4-9.0oC. Based on the field estimates of Ea•w and Te and the laboratory measurements of basal metabolic rate and thermal conductance, we conclude that there was a considerable nergy saving (456 kJ = 26% of •eq) during the first 10-11 days of life, due to parental brooding. After this period, when the parents stop brooding, the energy required for thermoregulation accounted for only 16% of F_•q. From 10 days after hatching onwards, the energy needed for activity increased considerably, up to 50% of Er,q just before fledging (Day 20). Comparison of the energy budgets of Arctic Tern chicks with the more southerly occurring closely related Common Tern (S. hirundo; Ricklefs and White 1981) revealed only a slightly higher energy expenditure in the Arctic Tern chicks. Received 5 April 1988, accepted 23 November 1988. ENERGY expenditure of chicks living in arctic and antarctic environments has been considered to be dominated by the costs for thermoregulation. Many physiologists 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, Jargensen and Blix 1985, Taylor 1985, Boersma 1986). However, the abiotic environment of chicks at high latitudes and the contribution of thermoregulatory costs to their total energy expenditure have not been quantified precisely. In addition to estimating thermoregulatory costs in relation to other energy requiring processes, interspecific comparison of closely related species from different latitudes should provide a better understanding of the influence of the polar environment on chick energy require-