Metabolism and Thermal Response in Winter-Acclimatized Pygmy Rabbits (Brachylagus idahoensis)

Resting metabolic rate of pygmy rabbits (0.89 ml O2 g -1 h -1 ) was high compared to other eutherian mammals, but not unusual among lagomorphs. The estimated size of the zone of thermoneutrality was ca. 8-9°C, with the lower critical temperature occurring between 15 and 20°C, depending on body mass. Minimum thermal conductance was lower and mean body temperature was higher than predicted for similarly sized mammals. Body temperature fluctuated >1°C within a 24-h period, but showed no circadian patterns. Pygmy rabbits are thermally stressed during harsh winters in Wyoming, but low thermal conductance, a high-energy source of food, and favorable microenvironments enhance survival.