Date of this Version
Physiological Zoology (May-June 1994) 67(3): 756-770.
I conducted afield experiment to examine the use of body fat as an energy re- serve by juvenile female Belding's ground squirrels, Spermophilus beldingi, prior to hibernation. Squirrels were divided into two groups: the squirrels in one group had their foraging times restricted by being placed in a cage forpart of each day for four consecutive days (deprived group), and the squirrels in the other group foraged ad lib. (ad lib. group). The deprived group foraged in its normal habitat morning and evening but had access only to water and lettuce while captive. Total body electrical conductivity (TOBEC), an in vivo method of estimating fat-free mass, was used to follow changes in body composition. The deprived group lost mass, while the ad lib. group gained mass. Total body electrical conductivity measurements indicated that the deprived group lost fat-free mass and not fat, whereas mass gained by the ad lib. group was mostly fat. This is consistent with an emphasis on fat anabolism prior to hibernation. I also show that the TOBEC method is affected by variation in stomach contents, and I evaluate conditions under which an intraspecific calibration equation is needed.