Sciuridae
 Sciurus niger
(fox squirrel)

Image Caption:
Thermal conservation is critical to the success of small mammals, which have a large surface area to volume ratio.  To reduce heat loss, squirrels den in tree cavities where available, and in winter months, especially during high winds (> 4 m/s) (Koprowski, 1994), squirrels spend more time in tree cavities and leaf nests than during summer.  In a study by Stephen P. Havera, occupied squirrel nesting boxes, which provide insulation similar to tree cavities, were an average of 25.9° C warmer than the ambient temperature.  The nest box’s lowest temperature was 8.3° C when the ambient temperature was -20.0° (Havera, 1979).  Tree cavities with small opening also block wind, keeping squirrels warmer during storms.

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Fox Squirrel (Sciurus niger rufiventer) in Tree Cavity (Hole)
Works Cited:  

Havera, S. P.  (1979).  Temperature Variation in a Fox Squirrel Nest Box.  The Journal of Wildlife Management, 43:251-253.

Koprowski, J. L.  (1994).  Sciurus niger.  Mammalian Species (479).  The American Society of Mammalogists.  (University of Arizona Link).

Image Location: United States, South Dakota, McCook County
Image Date: 2009JAN08
Image Species: Sciurus niger rufiventer 
(EXIF infomation is accurate – stamped in UTC).

Web Page and Pictures By Peter Leitheiser
Updated: 2009FEB04