Field and laboratory metabolism and thermoregulation in rhinoceros auklets

Abstract

Seabirds spend most of their lives at sea, except when visiting their breeding sites. Since the thermal conductivity of water is 25 times higher than that of air, seabirds resting on water lose heat and expend a considerable amount of energy for thermoregulation. For example, rhinoceros auklet (Cerorhinca monocerata), a medium-sized (480–620 g) alcid, spends most of its time floating on the sea. In order to estimate the cost of this behavior in terms of their daily energy expenditure (DEE), we studied rhinoceros auklets breeding on Teuri Island, Hokkaido Japan. We measured their resting metabolic rate (RMR) in air and on water by respirometry, and estimated their DEE by the doubly labeled water method. While RMR on water did not vary significantly between 10 °C and 15 °C, it was significantly higher at 5 °C. Air temperature (5.0–20.0 °C) had no effect on RMR. The DEE of free-ranging auklets averaged 1,005.5 kJ day−1 (±130.2, n = 3). Our results indicate that RMRs are elevated for auklets resting on water, particularly below their lower critical temperature (LCT), compared with in air. Accordingly, spending time above their LCT on water at any time of year will provide enhanced benefits, particularly to seabirds such as rhinoceros auklets which rest a considerable amount of time on water.

Resting costs too: the relative importance of active and resting energy expenditure in a sub-arctic seabird

“…Although the direct cost of thermoregulation in incubating kittiwakes has not been investigated yet, it has been studied in other bird species ( Gabrielsen et al, 1991 ), such as shorebirds with biparental care, where embryos near hatching contributed to 35–40% of the cost of incubation in both parents ( Norton, 1973 ). Alternatively, high T3 levels might be the result of increased heat loss from the brood patch ( Tapper et al, 2020 ), especially when spending time on water ( Umeyama et al, 2021 ). However, heat loss to the environment was adequately mitigated via vasoconstriction in the brood patch of black grouse (a subarctic species) when not incubating ( Tøien, 1993 ).…”