Burrowing and huddling in newborn porcupine: the effect on thermoregulation

The newborn cape porcupine Hystrix africaeaustralis is a precocial rodent. However, the newborn spends its first 9 weeks in the burrow. Heat production (oxygen consumption--VO2) and body temperature (Tb) were measured at various ambient temperatures (Ta) in newborn (4-8-week-old) porcupines, with a body mass between 1340-1993 g during summer, from the colony kept at the Mammal Research Institute, University of Pretoria. To assess the effect of huddling, these parameters were also measured in adult pairs of porcupines (Ta = 15 and 25 degrees C) kept together in the metabolic chamber and the values were compared with those obtained from single porcupines. Overall minimal thermal conductance was calculated for newborn and paired adult porcupines. The newborn porcupines can regulate their body temperature at Tas between 10-28 degrees C. VO2 measured at lower critical point is 0.602 +/- 0.08 ml/O2/g.h. At Ta = 10 degrees C, VO2 oscillated with a characteristic amplitude and frequency, while body temperature was well regulated. Huddling decreases the lower critical point. The overall minimal thermal conductance (0.044 +/- 0.002 ml O2/g.h.1 degree C) is higher than expected from body mass, so that the young are liable to lose heat rapidly. It is well known that the newborn porcupine spends a long period in the burrow and the results of this study suggest that this may be in order to conserve energy and presumably allocate it to growth. Apart from decreasing vulnerability, delaying foraging also avoids heat loss in the newborn porcupine.