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Seasonal Thermogenesis and Changes in Body Mass of Masked Shrews, Sorex cinereus

Joseph F. Merritt
Journal of Mammalogy
Vol. 76, No. 4 (Nov., 1995), pp. 1020-1035
DOI: 10.2307/1382596
Stable URL: http://www.jstor.org/stable/1382596
Page Count: 16
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Seasonal Thermogenesis and Changes in Body Mass of Masked Shrews, Sorex cinereus
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Abstract

Masked shrews (Sorex cinereus) are the most widely distributed shrews in North America, occurring from Alaska and Canada south into the northern one-half of the United States. Favorable winter survivorship of S. cinereus is reported from the Appalachian Mountains of Pennsylvania. In the present study, I examined the role of seasonal changes in resting metabolic rate, nonshivering thermogenesis, thermal conductance, and body mass of livetrapped shrews as mechanisms that enhance overwinter survivorship. Shrews were captured monthly from April 1992 to April 1993 in southwestern Pennsylvania. Temperatures at the ground surface ranged from -7 to 22°C, in February and April, respectively, and snow occurred from November to March. Mean resting metabolic rate for shrews was highest in autumn (8.30 ml O2 g-1 h-1) and lowest in spring (5.75 ml O2 g-1 h-1). Body temperature of shrews averaged 38.7°C. Thermal conductance averaged 0.79, ranging from a low in spring to a high in autumn. Mean nonshivering thermogenesis was lowest in summer (8.02 ml O2 g-1 h-1), and peaked in winter (14.60 ml O2 g-1 h-1). Capacity for nonshivering heat production in winter was almost twice that of summer. Nonshivering thermogenesis showed an inverse relationship to minimum ambient, ground surface, and subsurface temperatures. Body mass averaged 4.15 g and declined 53% from summer to winter. The favorable overwinter survivorship of S. cinereus 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 a decline in mass during winter.

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