Energy Metabolism and Body Composition of the Fox Squirrel

Abstract

The daily ad libitum intake of a commercial food (4.042 + 0.012[SD] kcal/g) by 12 adult fox squirrels (Sciurus niger) was 43 g. Nine specimens were fed for 7 days at 3 levels of nutrition (33, 67, and 100 percent of ad libitum). The average metabolizable energy value for all planes of nutrition was 3.210 kcal/g, and the nitrogen corrected metabolizable energy (MEn) was 2.880 kcal/g. Net energy values varied considerably among levels of feed intake. The maintenance energy requirement for adult fox squirrels was 162 kcal/g per day per Wkg075 of metabolizable energy. All feeding levels indicated a relatively high degree of nitrogen retention with a negative nitrogen balance exhibited only at the 33 percent level of nutrition. The energy content and the percentages of moisture, protein, fat, and ash were determined for the carcass of each animal. These data indicated that the condition of a squirrel population might be ascertained through a simple moisture analysis of captured animals. J. WILDL. MANAGE. 40(2):255-263 Since Lindeman (1942) formulated his concept of trophic dynamics, ecologists have become increasingly interested in the energy relationships of ecosystems. However, understanding of the energy dynamics of populations has been hampered by a general lack of knowledge concerning the metabolism of energy and nutrients by many organisms, including fox squirrels. The food habits of tree squirrels have been investigated by many workers (Baumgras 1944, Barber 1954, Nichols 1958, Dudderar 1967), as have the effects of food on squirrel activity, behavior, and reproductive success (Seton 1929, Allen 1943, Uhlig 1956, Brown and Yeager 1945, Nixon et al. 1968). Ludwick et al. (1969) and Montgomery et al. (1975) investigated the energy metabolism of the gray squirrel (S. carolinensis), but to date there has been no attempt to assess the energy and nutrient metabolism of the fox squirrel. Although nutrients are an important parameter, it is likely that energy may be the limiting factor in animal population nutrition. This study was undertaken from October 1973 to June 1974. Specific objectives were to (1) assess the energy requirements of adult fox squirrels, (2) study the effect of planes of nutrition on the efficiency of energy utilization, (3) measure the nitrogen balance of adult fox squirrels under variations in both caloric and protein intake, and (4) determine the energy content, and the percentage fat, protein, moisture, and ash of the carcass for specimens at various levels of nutrition.