Ambient temperatures in hibernacula and their energetic consequences for alpine marmots Marmota marmota

Abstract

Temperatures inside natural winter burrows of alpine marmots ( T bur) dropped exponentially throughout the hibernation season from about 12°C in autumn to almost 0°C in spring. Laboratory measurements of oxygen consumption ( V̇O 2) showed that torpid marmots have minimal energy expenditure at ambient temperatures ( T a) above 5°C. Metabolism increased with decreasing T a below 5°C. At T a ≈ 0° C, V̇O 2 was already four times higher than the minimal value. T bur was below 5°C for about two thirds of the hibernation season. The more animals hibernated together in a burrow, the latter T bur fell below this critical threshold. Hence, overwintering conditions in the natural habitat are severe for the animals, but mitigated by social hibernation.