Use of Bioelectrical Impedance Analysis (BIA) for Predicting Body Fat in Three Populations of Hibernating Black Bears

Bioelectrical impedance analysis (BIA) is a tool used to provide a measure of body water content and total body fat in an organism. Recently, researchers have validated BIA against tritiated water techniques in the laboratory and proposed it as a fast, non-invasive method for assessing body condition in free-ranging black bears. In the present study, we field tested BIA as a plausible tool for investigating body fat utilization during hibernation by three black bear populations in the Rocky Mountains. Body fat content in the fall ranged from a mean of about 39% for a group of large, lactating females down to about 29% by two groups of bears consisting of males and mostly non-lactating females. Daily rates of body fat use were greater for the larger, lactating female group than either of the other two groups. Although the fat data determined by BIA appear useful in terms of trends and relative changes, many of the absolute values are inconsistent and perhaps inaccurate. Because BIA is so sensitive to a variety of factors typical of field conditions, we recommend it not be used as the sole source for assessing body condition of large animals such as black bears.