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1 June 2009 Seasonal Metabolic Acclimatization in a Northern Population of Free-Ranging Snowshoe Hares, Lepus americanus
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Seasonal acclimatization in high-latitude endotherms may involve increases or reductions in body size and metabolic rate to, respectively, augment thermoregulatory capacity or reduce energy requirements. We investigated seasonal acclimatization in a northern population of wild snowshoe hares (Lepus americanus) that is exposed to low food availability and extremely cold temperatures in winter. Snowshoe hares were livetrapped and transported to a nearby mobile laboratory. Hares were placed in a metabolic chamber and oxygen consumption was measured for 55 min at each of the following temperatures: 10°C, 0°C, −10°C, −15°C, and −20°C. Hair length and density were measured on a sample of collected hares. Snowshoe hares maintained similar body mass and body temperature between the seasons, but average resting metabolic rate and thermal conductance were, respectively, 20% and 32% lower in winter than in autumn. The lower critical temperature was −10°C to −15°C in winter and 0°C to −10°C in autumn. Guard hairs were 36% longer and 148% denser in winter than autumn, whereas downy hairs were the same length but 128% denser in winter than autumn. Collectively, these results suggest that resource constraints associated with a herbivorous diet in regions and seasons of poor forage quality favors an energetically conservative approach to winter acclimatization.

Michael J. Sheriff, Louise Kuchel, Stan BOUTIN, and Murray M. Humphries "Seasonal Metabolic Acclimatization in a Northern Population of Free-Ranging Snowshoe Hares, Lepus americanus," Journal of Mammalogy 90(3), 761-767, (1 June 2009).
Received: 29 July 2008; Accepted: 1 September 2008; Published: 1 June 2009

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