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Physiology and Pharmacology of Temperature Regulation

Body temperature changes induced by huddling in breeding male emperor penguins

¹Institut Pluridisciplinaire Hubert Curien, Département Ecologie, Physiologie et Ethologie and Département Interactions Physique, Chimie et Vivant, Unité Mixte de Recherche (UMR) 7178, Centre National de la Recherche Scientifique and Université Louis Pasteur, Strasbourg, France; and ²Département d'Ecologie et Gestion de la Biodiversité, UMR 5176, Centre National de la Recherche Scientifique and Muséum National d'Histoire Naturelle, Brunoy, France

Submitted 29 December 2005 ; accepted in final form 4 September 2006

Huddling is the key energy-saving mechanism for emperor penguins to endure their 4-mo incubation fast during the Antarctic winter, but the underlying physiological mechanisms of this energy saving have remained elusive. The question is whether their deep body (core) temperature may drop in association with energy sparing, taking into account that successful egg incubation requires a temperature of about 36°C and that ambient temperatures of up to 37.5°C may be reached within tight huddles. Using data loggers implanted into five unrestrained breeding males, we present here the first data on body temperature changes throughout the breeding cycle of emperor penguins, with particular emphasis on huddling bouts. During the pairing period, core temperature decreased progressively from 37.5 ± 0.4°C to 36.5 ± 0.3°C, associated with a significant temperature drop of 0.5 ± 0.3°C during huddling. In case of egg loss, body temperature continued to decrease to 35.5 ± 0.4°C, with a further 0.9°C decrease during huddling. By contrast, a constant core temperature of 36.9 ± 0.2°C was maintained during successful incubation, even during huddling, suggesting a trade-off between the demands for successful egg incubation and energy saving. However, such a limited drop in body temperature cannot explain the observed energy savings of breeding emperor penguins. Furthermore, we never observed any signs of hyperthermia in huddling birds that were exposed to ambient temperatures as high as above 35°C. We suggest that the energy savings of huddling birds is due to a metabolic depression, the extent of which depends on a reduction of body surface areas exposed to cold.

huddling; energy saving; hypothermia; emperor penguins; Antarctica

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