Seasonal thermogenesis and body-mass dynamics of Clethrionomys gapperi

Examined the role of seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), and body mass of southern red-backed voles as adaptations that enhance over-winter survivorship. Average RMR for voles was highest in September and April and lowest in July. No significant changes in RMR occurred on a seasonal basis. Mean NST was lowest in summer, increased throughout autumn, peaked in winter, and declined through spring. Maximum NST capacity occurred in mid-March, following a period in which ambient, ground, and subsurface temperatures reached an annual low. NST values showed an inverse relationship to minimum environmental temperature at the capture site. Mean body mass exhibited significant monthly variation. Average mass dropped significantly between September and November and increased from a low in January to the peak mass in May concomitant with reproductive activity. The favorable over-winter survival is due in part to the ability of this species to increaes thermogenic capacity by means of nonshivering thermogenesis coupled with energy conservation in the form of growth retardation during winter. Red-backed voles may opt to channel energy into growth or thermoregulation on a priority basis as dictated by food availability and temperatures encountered during their foraging. -from Authors