The role of seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), and body mass of livetrapped southern red-backed voles (Clethrionomys gapperi) as adaptations that enhance over-winter survivorship were examined in this study. 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. Analysis of mass changes of individuals conformed to the above trends. The favorable over-winter survival of C. gapperi is due in part to the ability of this species to increase 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.

No abstract

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Table) Deermice were exposed to photoperiods simulating either early winter photoperiod ("winter replicates") or early spring photoperiod ("spring replicates") before experiencing 14-day treatment periods designed to assess the effects of ambient temperature and photoperiod on nonshivering thermogenesis (NST). These treatments consisted of the four combinations of low (5°C) or high (25°C) temperatures and short (8L : 16D) or long (16L : 8D) photoperiod. In both winter and spring replicates, only those mice exposed to both low temperature and short photoperiod experienced significantly elevated levels of NST. In the spring replicates, those mice exposed to both high temperature and long photoperiod experienced significant loss of NST. These results support the hypothesis that photoperiod and ambient temperature interact to trigger changes in NST.

2002. Maximizing survivorship in cold: thermogenic profiles of non-hibernating mammals. [In: Theriology at the turn of a new century. J. Gliwicz, ed]. Acta Theriologica 47, Suppl. 1: 221-234.Winter-active small mammals residing in seasonal environments employ many different behavioral, anatomical and physiological mechanisms to cope with cold. Herein we review research on survival mechanisms in cold employed by small mammals with emphasis on the families Soricidae, Muridae and Sciuridae. The focus of this review is on research delineating the role of seasonal changes in resting metabolic rate (RMR), nonshivering thermogenesis (NST), body mass, and communal nesting in enhancing winter survivorship of six species of small mammals (masked shrew Sorex cinereus, short-tailed shrew Blarina brevicauda, southern red-backed vole Clethrionomys gapperi, white-footed mouse Peromyscus leucopus, deer mouse P. maniculatus, and southern flying squirrel Glaucomys volans) residing in the Appalachian Mountains of Pennsylvania, USA. Each species shows good over-winter survivorship but exhibits a different suite of mechanisms to maximize survival in cold. B. brevicauda, S. cinereus, and G. volans show slight increases in RMR during winter, whereas Peromyscus and C. gapperi exhibit decreased RMR overwinter. All six species experience elevated NST in winter. The comparatively low RMR and NST of G. volans during winter was attributable to a decreased energy expenditure due to a larger body mass, coupled with communal nesting in cavities of trees that provided insulation from low ambient temperatures. Squirrels nesting singly experienced a longer period of elevated NST in winter and higher mean NST year-round than did squirrels nesting communally. Energy conservation in the form of growth retardation in winter was exhibited by C. gapperi and S. cinereus but not the other species.