Physiological ecology of the arctic ground squirrel: Energy metabolism, torpor, and behavioral endocrinology

I monitored seasonal changes in body condition and dates of immergence into and emergence from hibernation in a natural population of arctic ground squirrels (Sphermophilus parryii kennicottii) living on the North Slope of Alaska. Age and sex differences in changes of body condition and hibernation chronology are attributable to sex differences in energetic costs associated with preparation for reproduction and differences in reproductive status within males. While winters are long and environmental conditions faced by arctic ground squirrels in northern Alaska are extreme, the timing of hibernation did not differ appreciably from patterns observed in Sciurid populations living in temperate latitudes. To determine the environmental conditions faced by S. parryii during hibernation and to investigate the effect of overwinter temperature on change in body condition of the individual, I instrumented 18 burrow sites with temperature-sensitive data loggers to record soil temperature at hibernacula depth. Burrow sites did not differ significantly in soil temperature over years, but significant thermal differences were observed among burrows. Burrows with more shrubby vegetation accumulated deeper snow and had higher overwinter temperatures than did windswept sites. Females hibernated at warmer sites than did males and adults hibernated at warmer sites than juveniles. Repeated measures of overwinter changes in body condition were not significantly correlated with winter soil temperatures for any age or sex class. To determine the energetic cost associated with hibernation under arctic conditions, I measured metabolic rate, respiratory quotient, and body temperature of arctic ground squirrels in steady-state torpor. At ambient temperatures below 0...