R.C. Cook | Geology Reports

USGS2008

Relations between nutritional condition and survival of North American elk Cervus elaphus

We related annual and seasonal survival of four populations of elk Cervus elaphus in the Pacific Northwest, USA, to measures and indices of individual nutritional condition. Among populations, for all mortality (human and non-human causes) sources inclusive, annual survival of adult females was correlated with a rump body condition score (rs = 0.627, P = 0.071), and survival over spring-summer-autumn (SSA) was correlated with mean ingesta-free body fat (IFBF; rs = 0.567, P = 0.088) and rump body condition score (rBCS; rs = 0.615, P = 0.050). For non-human mortality sources only, survival through SSA was correlated with IFBF (rs = 0.567, P = 0.088) and rBCS (rs = 0.615, P = 0.050), and survival over winter was correlated with withers body condition score (rs = 0.677, P = 0.045). For human-caused mortality sources only, survival over SSA was correlated with rBCS (rs = 0.696, P = 0.036) and IFBF (rs = 0.696, P = 0.036). For individuals, logistic analysis found that individual likelihood of dying from all mortality sources inclusive was best predicted (??2 = 8.3, P = 0.004, ?? = -1.24) by longissimus dorsi (loin) muscle thickness, a measure of protein catabolism. For only non-human mortality sources, a model (??2 = 16.1, P = 0.0003) containing both loin muscle thickness (??2 = 5.7, P = 0.017, ??= -1.02) and percent ingesta-free body fat (??2 = 4.9, P = 0.027, ?? = -0.35) best predicted individual susceptibility to mortality. Odds ratios indicated that odds of dying increased approximately 3X for each centimeter of loin muscle catabolized and 1.4X for each percent less body fat. No condition indices at the individual level were related to survival from human-caused mortality sources. Our study populations were characterized by low-marginal condition (i.e. mean ingesta-free body fat levels of 5.9-12.3% for lactating cows in late autumn); this likely increased the prominence of measures of muscle catabolism relative to fat accretion in influencing individual elk survival. Elk populations throughout the Pacific Northwest likely show similar condition levels, and consequently individuals are predisposed to mortality to a much greater degree than under optimal foraging conditions. Management strategies which assume that nutritional condition affects vulnerability only at or near condition levels associated with ecological carrying capacity (i.e. near starvation mortality) may overestimate the impact of proximate mortality factors on adult female elk. ?? Wildlife Biology (2008).

Wildlife Biology↗

USGS2004

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 ≥ 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.

Wyoming↗