Nutritional condition of northern Yellowstone elk

We estimated nutritional condition for 96 female northern Yellowstone elk (Cervus elaphus nelsoni) during mid- to late winter 2000, 2001, and 2002. Neither year nor capture location significantly influenced any measure of condition (body fat, body mass, and longissimus dorsi thickness; P greater than or equal to 0.14). Overall, age = 8.9 years +/- 0.4 SE, body fat = 9.5% +/- 0.4, body mass = 235.1 kg +/- 2.2, and longissimus dorsi muscle thickness = 5.6 cm +/- 0.1. Despite an age segregation pattern across the winter range (P = 0.016), we found no evidence of bias in our estimates of nutritional condition due to this pattern because condition was unrelated to age. Yearly pregnancy and lactation rates of all cows ranged from 78 to 84% and 8 to 16%, respectively, at the time of capture. Lactational status significantly influenced body condition (P = 0.003), with lactating cows having 50% less body fat than nonlactating cows. Probability of pregnancy observed for elk that we captured followed a logistic curve as a function of body fat levels. Based on mid- to late winter body fat levels, we would predict low mortality of adult cows during mild to normal winters. We suggest the possibility of nutritional limitations acting on this herd through summer-autumn forage conditions, in association with limitations during harsh winters.