Energy Metabolism of the Eastern Gray Squirrel

Abstract

Two feeding experiments were performed with adult and immature gray squirrels (Sciurus carolinensis). In the first experiment 18 adult squirrels, fed at three planes of nutrition (33, 67, and 100 percent of ad libitum), were used to determine the maintenance energy requirements and the effect of plane of nutrition on the metabolizable and net energy values, using a commercial laboratory rodent diet (4.125 kcal/g). The average metabolizable energy value for all planes of nutrition for adult squirrels was 2.992 kcal/g, and 71.8 percent of the gross energy was metabolized. Net energy values varied considerably among levels of feed intake and methods of calculation. The maintenance energy requirement for a 500 g squirrel was calculated to be about 137 kcal/day of metabolizable energy or 33.3 g/ day of the experimental food. Voluntary intake in calories (about 203 kcal) exceeded the maintenance requirement by about 32 percent. In the second experiment, 24 immature squirrels were used to determine the effect of plane of nutrition (64, 76, 88, and 100 percent ad libitum) on the digestible and metabolizable energy values of the diet. Analysis of variance showed that the influence of the level of food intake was not significant both for the digestible and metabolizable energy values (P > 0.05). The mean values were 3.535 kcal/ g and 3.444 kcal/g for the digestible and metabolizable energy values, respectively. A 42-percent decrease of average food intake between January and March was noted in six ad libitum fed immature squirrels. Approximately 35 percent of the squirrels trapped and held through the adjustment period died prior to the beginning of the feeding trials. The food habits of the tree squirrels have been investigated by several workers (Barber 1954, Nichols 1958, Dudderar 1967) and the influence of food, particularly its scarcity, on squirrel activity, behavior, movements, and reproductive attainment has been discussed by others (Seton 1928, Allen 1943, Uhlig 1956, Brown and Yeager 1945). There has been no attempt to assess the nutritional requirements of the gray squirrel. Caloric requirements, and the digestible, metabolizable, and net energy values of food are unknown. This preliminary study attempted to determine the energy requirements for adult squirrels, study the effect of planes of nutrition on efficiency of energy 1 Release No. 69-1 of the Virginia Cooperative Wildlife Research Unit. This project was financed largely by the Virginia Agricultural Experiment Station. Acknowledgment is made to the Departments of Animal Science, Forestry and Wildlife, and Biochemistry and Nutrition for the use of facilities and equipment. utilization in both immatures and adults, and develop techniques for use in future nutritional studies.