Nutritional condition models for elk: Which are the most sensitive, accurate, and precise?

Traditionally, biologists have developed indices that assess nutrition and condition of wild ungulates. However. many attempts to validate such indices have failed to indicate the range of conditions under which they work. Furthermore. Such validation tests often fail to identify sensitivity to small but biologically meaningful differences, and emphasize statistical rather than biological relationships. We evaluated 20 models that were developed to assess nutritional condition of Rocky Mountain elk (Cervus elaphus nelsonii). We analyzed sensitivity, bias, accuracy. precision applicability across a wide range of body conditions, and field practicality. Because models were derived using captive elk. we incorporated data from 6 wild cows to assess suitability of condition-index models for free-ranging elk. We found that most condition indicators available to biologists were weakly related to actual nutritional condition, were insensitive to small changes in condition, or often showed nonlinear relations that restricted their value to a narrow range of body condition. Art arithmetic combination of a rump body-condition score and subcutaneous rump-fat thickness for live animals, and a modified carcass-evaluation score for dead animals, were the most sensitive and accurate indices of nutritional condition that we tested.