Accuracy of body weight prediction in Alpine ibex (Capra ibex, L. 1758) using morphometry

The relationship between weight and body measurements of 227 Alpine ibex Capra ibex (162 males and 65 females, age range: 2-16 years) were analysed by linear and multiple regression. The animals were live-captured across all seasons of the year, in the Western Italian Alps, 1986-1994. The relationship between weight and body measurements changed with sex and season. In male ibex, the best annual estimation of the body weight was obtained using as predictor variables the squared value of the chest girth and age. In females, the best predictive variables were age, total body length and withers height. Age was always selected as a predictor variable, when considered in the prediction models. The use of chest girth and the squared value of the chest girth as predictive variables in the regression equation, being the most highly correlated linear measurements with total weight, did not result in an accurate prediction of ibex body weight. The best prediction was obtained using age and different linear measurements in stepwise multiple regression, nevertheless the standard error of the estimate and the magnitude of the 95% prediction interval were great. The use of linear measurements cannot be considered accurate nor precise predictors of body weight in Alpine ibex.