Body temperature patterns during hibernation in a free-living Alaska marmot (Marmota broweri)

Marmota broweri is endemic to arctic Alaska. We implanted data loggers into one free-living subadult female in August 2007 to record body temperature (Tb). Seasonal heterothermy lasted for 224 days (10 September to 21 April). Midwinter torpor bout length (mean ± SD) was 13.91 ± 3.56 days and duration of interbout euthermy was 18.43 ± 2.55 hr. Unlike other marmot species, torpor entry during midwinter was consistently characterized by two distinct cooling rates differing by about 10-fold and separated by a transient temperature increase. Minimum hibernaculum temperature was - 14.97 °C in February (7 month mean: - 7.33 °C). Minimum Tb was 1.01 °C when defending a 15.5 °C thermal gradient. At least six animals emerged from the hibernaculum suggesting that communal hibernation may be a strategy to reduce metabolic costs while maintaining above-freezing Tb.