Thermoregulation and repeatability of oxygen-consumption measurements in winter- acclimatized North American porcupines (Erethizon dorsatum)

We measured the thermoregulatory responses of 13 North American porcupines (Erethizon dorsatum) to low ambient temperatures during respirometry trials in both air and a helium-oxygen gas mixture (helox). The objective was to quantify the energy metabolism of porcupines under varying ambient temperatures. The basal metabolic rate of our winter-acclimatized porcupines was higher than expected for animals of their body size, whereas thermal conductance was lower than allometric predictions. The increase in metabolic rate that we observed at -20°C was ca. 2 X BMR, although this was not the animals' maximum thermogenic capacity. The mean increase in thermal conductance for individuals placed in a helox atmosphere over that measured in an oxygen atmosphere was 1.91 and this represented a metabolic rate of ca. 3 X BMR at -20°C. We also determined that the repeatability of oxygen-consumption measurements below thermoneutrality were highly repeatable over medium-length time intervals (mean = 11 days) for both absolute and residual values.