PREDICTING PARTURITION RATE OF CARIBOU FROM AUTUMN BODY-MASS

Body condition indices are potentially useful as predictors of fecundity in ungulates. We updated a logistic-regression model of the relationship between probability of parturition for adult caribou (Rangifer tarandus) and body mass during the previous autumn (model significance, P = 0.025). We also derived a model for herd parturition rate on the basis of the logistic-regression for individual females and the mean and standard deviation of body mass. Small shifts in mass distribution result in relatively large changes in parturition rate, emphasizing the importance of minor changes in forage quality and availability, and indicating a need for representative masses for a herd when attempting to make predictions. Because of the difficulties in obtaining unbiased samples and the serious errors inherent in not doing so, we recommend estimating parturition rate directly by determining the reproductive status of a sample of radio-collared adult females or through systematic counts of newborn calves, antlers, and udders.