Predicting Body Condition of Bears via Two Field Methods

Bioelectrical impedance analysis (BIA) and isotopic water dilution have been proposed as methods suitable for determining the body composition of wild bears. We investigated the accuracy of these 2 techniques in a single-blind study. Water dilution was a more precise predictor of the body fat content of black bears (Ursus americanus) and brown bears (U. arctos) than was BIA, as indicated by comparison of the standard error of the estimate (SEE; 2.31% vs. 3.27%). The mean of the estimates from both methods predicted bear body fat content with the least error (SEE = 1.67%). The magnitude of the error for either method was not significantly related to body mass, lipid content, or animal age. Accurate, repeatable BIA estimates require extensive training and experience to standardize measurement conditions. Isotopic water dilution has fewer error sources but requires laboratory analyses.