Bioenergetics of a Woodlot Gray Squirrel Population

The gray squirrel (Sciurus carolinensis) population in an isolated 3.2-ha, overmature woodlot was estimated by trap-retrap procedures for each of the 4 seasons of 1 year, September 1971-September 1972. The energy requirements of these gray squirrels were extrapolated from the caloric intake determined from gray squirrels housed in large outdoor pens. Mean dry weight production and caloric values of the 20 most important foods available to squirrels were determined from samples collected on a seasonal basis, and the energy flow through the woodlot squirrel population was calculated. The average daily food consumed by the penned squirrels varied from 50.9 $\text{g}/\text{W}^{0.75}$ (W = live weight in kg) for subadults to 55.6 $\text{g}/\text{W}^{0.75}$ for adults and 60.7 $\text{g}/\text{W}^{0.75}$ for juveniles. These squirrels voluntarily restricted their food in the winter. Our wild population had a seasonal average of 15.7 squirrels/ha, or 0.71 g/m2/season, and an average energy density of 1.25 kcal/m2/season. The food energy available to this population during the year was 282.75 kcal/m2/year. Of this energy, 32.0 percent was ingested and 23.9 percent was metabolized, of which 23.6 percent was utilized for maintenance and only 0.3 percent for production. Our investigations indicated that this sciurid, with a wide food-base of both reproductive and vegetative plant parts, efficiently utilized the food available. Both the utilization efficiency of food energy and the energy density of this squirrel population were greater than has been reported for other small mammals.