Thermoregulatory Adaptations to Cold in Winter-Acclimatized Long-Tailed Ducks (Clangula Hyemalis)
The extreme thermal conditions that prevail during wintertime in maritim arctic and subarctic regions are probably the reason why so few homeotherms choose to winter there. In addition to low air temperatures, aquatic animals are exposed to water temperatures as low as -1.8 °C. In order to remain homeothermic in water, some animal groups, such as the pinnipeds and cetaceans, have evolved a thick insulating layer of blubber (Aschoff, 1981). Other groups, such as otters and birds are dependent on a water-repelling pelt or plumage that creates an insulating air layer around the animal (Costa and Kooyman, 1982, Kooyman et al., 1976). The only birds that spend most of their time on the sea surface during winter are found among loons, auks and seaducks. Few studies have been made to investigate the particular adaptations that these species, which may winter as far north as 71 °N, have evolved in order to live in such harsh conditions. In a previous study (Jenssen et al., 1989) we studied the thermoregulation of Common eiders (Somateria mollissima) acclimatized to winter conditions. The study showed that the Common eider, which is the largest of the seaducks, has evolved a highly insulative plumage. This species, in addition, depends upon extensive use of peripheral vasoconstriction to minimize its heat loss. The basal metabolic heat production of the Common eider is not particurlarly high, as is found to be the case among other seabirds from high lattitudes (Ellis, 1984).
KeywordsHeat Production Thermal Insulation Allometric Equation Standard Metabolic Rate Peripheral Vasoconstriction
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