John G. Cook

EFFECTS OF SUMMER-AUTUMN NUTRITION AND PARTURITION DATE ON REPRODUCTION AND SURVIVAL OF ELK

: Recent declines in numbers and juvenile recruitment in many elk (Cervus elaphus) herds in the western U.S. has sparked interest in factors that may cause these declines. Inadequate nutrition or delayed parturition, the latter of which may be caused by inadequate numbers of mature bulls (i.e., highly skewed sex ratios), may have separate or synergistic effects on population dynamics and productivity. We evaluated the implications of late parturition and summer-autumn nutrition on reproduction and survival of Rocky Mountain elk (C. e. nelsoni) using a captive herd of 57 cow elk. We induced early (Sep) and late breeding (Oct) and 3 levels of summer-autumn nutrition on the cows. Food was offered ad libitum at 3 levels of digestible energy (DE): high = 2.9-3.0 kcal of DE/g of diets, medium = 2.6-3.0 kcal/g, and low = 2.3-3.0 kcal/g. Within these ranges, DE content was gradually reduced from late June through early November to mimic seasonal changes in the wild. During summer and autumn, we measured calf growth; body mass, nutritional condition, and breeding dynamics of cows; and growth and pregnancy of yearlings. We also measured carry-over (i.e., time-lag) responses including over-winter calf and cow survival and parturition date and birth mass, as functions of previous summer-autumn nutrition and previous parturition date. Between autumn 1995 and spring 1998, we conducted 2 years of parturition-date, summer-autumn nutrition experiments, 2 winters of calf survival experiments, and 1 winter of cow survival experiments. Early birth provided calves with more time to grow before onset of winter. This “head-start” advantage was maintained through late autumn, but its magnitude was diluted in some instances due to faster growth of some late-born calves. Body mass, body fat, and timing and probability of conception by cows in autumn were little influenced by parturition date the previous spring. Summer-autumn nutrition significantly affected calves and their mothers. Growth of calves in the low and medium nutrition groups ceased by mid-September and late October. By December, calves in the high nutrition group were 40% and 70% heavier than calves in the medium and low groups, respectively. Cows in the high nutrition group accumulated about 75% and 300% more fat than cows in the medium and low groups by mid-October. Eighty percent of cows in the low nutrition group failed to conceive, and those in the medium group bred 10–14 days later than cows in the high group. Summer-autumn nutrition of calves influenced their probability of becoming pregnant as yearlings. Probability of pregnancy approached 100% for those yearlings that had high summerautumn nutrition as calves and yearlings, despite near starvation their first winter of life. Winter survival of calves was related to their size at the onset of winter. Smaller calves lost more body mass daily than did large calves, and thus they survived fewer days through winter. Summer-autumn nutrition largely determined calf body size at the start of winter and, consequently, determined the proportion of winter survived. Survival of cows over winter was as related to body fat at the onset of winter as it was to nutrition during winter. Carry-over effects of summer-autumn nutrition and parturition date on birth characteristics the following spring were minor. We detected no significant carry-over effect of summer-autumn nutrition or autumn condition on birth mass, although reduced condition in autumn delayed subsequent parturition date. Extent of body fat depletion in cows during the winter-survival experiments in 1998 accounted for 45% of the variation in parturition date. Ninety percent depletion delayed parturition an average of 34 days. Delayed parturition, of a magnitude expected due to highly skewed sex ratios (3 weeks under extreme conditions), probably has only a weak influence on vital rates of free-ranging elk. In contrast, fat accretion and probability of pregnancy of cows, and growth and overwinter survival of calves, were sensitive to small (10–20%) differences in DE content of food. Digestible energy levels of our 2 lower nutrition levels reflect DE ranges reported for large ungulate herds during summer and autumn in western North America. Thus, our data suggest that limiting effects of summer-autumn nutrition on populations may be greater than often assumed, perhaps greater than those during winter in some ecosystems, and consequently indicate a need for greater understanding of nutritions influence on population dynamics and how this influence varies across space and time. To enhance future research, we present animal- and vegetation-based guidelines for evaluating nutritional influences on elk populations.

Animal migration amid shifting patterns of phenology and predation: lessons from a Yellowstone elk herd

Migration is a striking behavioral strategy by which many animals enhance resource acquisition while reducing predation risk. Historically, the demographic benefits of such movements made migration common, but in many taxa the phenomenon is considered globally threatened. Here we describe a long-term decline in the productivity of elk (Cervus elaphus) that migrate through intact wilderness areas to protected summer ranges inside Yellowstone National Park, USA. We attribute this decline to a long-term reduction in the demographic benefits that ungulates typically gain from migration. Among migratory elk, we observed a 21-year, 70% reduction in recruitment and a 4-year, 19% depression in their pregnancy rate largely caused by infrequent reproduction of females that were young or lactating. In contrast, among resident elk, we have recently observed increasing recruitment and a high rate of pregnancy. Landscape-level changes in habitat quality and predation appear to be responsible for the declining productivity of Yellowstone migrants. From 1989 to 2009, migratory elk experienced an increasing rate and shorter duration of green-up coincident with warmer spring-summer temperatures and reduced spring precipitation, also consistent with observations of an unusually severe drought in the region. Migrants are also now exposed to four times as many grizzly bears (Ursus arctos) and wolves (Canis lupus) as resident elk. Both of these restored predators consume migratory elk calves at high rates in the Yellowstone wilderness but are maintained at low densities via lethal management and human disturbance in the year-round habitats of resident elk. Our findings suggest that large-carnivore recovery and drought, operating simultaneously along an elevation gradient, have disproportionately influenced the demography of migratory elk. Many migratory animals travel large geographic distances between their seasonal ranges. Changes in land use and climate that disparately influence such seasonal ranges may alter the ecological basis of migratory behavior, representing an important challenge for, and a powerful lens into, the ecology and conservation of migratory taxa.

Development of predictive models of nutritional condition for Rocky Mountain elk

Despite its preeminence as a game species in North America, little research exists to validate nutritional condition indices for Rocky Mountain elk (Cervus elaphus nelsonii). We developed and calibrated indices of nutritional condition for live and dead Rocky Mountain elk. Live-animal indices included 20 serum and 7 urine chemistry variables, a body-condition score (BCS), thickness of subcutaneous fat and selected muscles using ultrasonography, bioelectrical impedance analysis (BIA), and body mass. Dead-animal indices included femur and mandible marrow fat, 3 kidney fat indices, and 2 carcass-scoring methods. Forty-three captive-raised cows (1.5 to 7 years old) were randomly divided into 3 seasonal groups (Sep, Dec, and Mar). Within seasonal groups, elk were fed different diets to induce a wide range of condition; all were fed identical diets 7 days prior to sampling to eliminate short-term nutritional effects. Cows were euthanized and homogenized for chemical analysis of fat, protein, water, and ash content. Estimates of fat and gross energy (GE) were compared to each condition indicator using regression, with age and season as covariates. Relations between condition and thyroxine (T 4 ) and insulin-like growth factor (IGF-1) varied seasonally, and the relation between condition and mandible marrow fat varied among ages. Subcutaneous fat depth and BCS were most related to condition for live animals (r 2 ≥ 0.87, P < 0.001); carcass scores and kidney fat were most related to fat and GE for dead animals (r 2 ≥ 0.77, P < 0.001); and IGF-1 and T 4 were the only serum and urine indices at least moderately related to condition (r 2 ≥ 0.54, P < 0.001). Nearly all other serum and urine indices, bone marrow indices, and BIA were either poorly correlated with condition or exhibited highly nonlinear relations. These results identify several indices of condition useful for assessing nutritional condition of live or dead elk, and indicate a number of previously used techniques that correlate poorly with total body fat.

Nutritional Condition of Northern Yellowstone Elk

Abstract 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.

Linking anti-predator behaviour to prey demography reveals limited risk effects of an actively hunting large carnivore

Ecological theory predicts that the diffuse risk cues generated by wide-ranging, active predators should induce prey behavioural responses but not major, population- or community-level consequences. We evaluated the non-consumptive effects (NCEs) of an active predator, the grey wolf (Canis lupus), by simultaneously tracking wolves and the behaviour, body fat, and pregnancy of elk (Cervus elaphus), their primary prey in the Greater Yellowstone Ecosystem. When wolves approached within 1 km, elk increased their rates of movement, displacement and vigilance. Even in high-risk areas, however, these encounters occurred only once every 9 days. Ultimately, despite 20-fold variation in the frequency of encounters between wolves and individual elk, the risk of predation was not associated with elk body fat or pregnancy. Our findings suggest that the ecological consequences of actively hunting large carnivores, such as the wolf, are more likely transmitted by consumptive effects on prey survival than NCEs on prey behaviour.

Nutrition-growth relations of elk calves during late summer and fall

We report nutrition-growth relations in juvenile Rocky Mountain elk (Cerous elaphus nelsoni) from mid-August through mid-November. Data were generated from 3, 18-day experimental trials in 1993 with 42 calves, and from general feeding and growth data collected in 1991 with 25 calves. Intake of digestible energy was linearly correlated with growth rate and accounted for 53-89% of the variation in calf growth. Maximum daily digestible energy intake and growth rates were 368 kcal/kg BM 0.75 and 0.70 kg/day in late August and early September and 342 kcal/kg BM 0.75 and 0.33 kg/day in mid-November. Intake-specific growth rates declined after late September, suggesting a seasonal influence on growth-intake relations. We developed a deterministic model of growth to compare body mass dynamics over autumn of calves on an optimum diet (i.e., 3.3-2.95 kcal of digestible energy/g of forage) versus calves on diets available to free-ranging elk (2.66-1.86 kcal/g). Model projections indicated a 21% difference in body mass of the 2 groups by mid-December due to the lower concentration of digestible energy in diets of free-ranging calves. Our results confirm the importance of nutrition in late summer and fall for growth of elk calves, suggest a mechanism linking dietary quality during this time to winter survival, and demonstrate the importance of evaluating forage quality for reliable assessment of habitat quality on elk summer and autumn ranges.

Revisions of Rump Fat and Body Scoring Indices for Deer, Elk, and Moose

Abstract Because they do not require sacrificing animals, body condition scores (BCS), thickness of rump fat (MAXFAT), and other similar predictors of body fat have advanced estimating nutritional condition of ungulates and their use has proliferated in North America in the last decade. However, initial testing of these predictors was too limited to assess their reliability among diverse habitats, ecotypes, subspecies, and populations across the continent. With data collected from mule deer (Odocoileus hemionus), elk (Cervus elaphus), and moose (Alces alces) during initial model development and data collected subsequently from free-ranging mule deer and elk herds across much of the western United States, we evaluated reliability across a broader range of conditions than were initially available. First, to more rigorously test reliability of the MAXFAT index, we evaluated its robustness across the 3 species, using an allometric scaling function to adjust for differences in animal size. We then evaluated MAXFAT, rump body condition score (rBCS), rLIVINDEX (an arithmetic combination of MAXFAT and rBCS), and our new allometrically scaled rump-fat thickness index using data from 815 free-ranging female Roosevelt and Rocky Mountain elk (C. e. roosevelti and C. e. nelsoni) from 19 populations encompassing 4 geographic regions and 250 free-ranging female mule deer from 7 populations and 2 regions. We tested for effects of subspecies, geographic region, and captive versus free-ranging existence. Rump-fat thickness, when scaled allometrically with body mass, was related to ingesta-free body fat over a 38–522-kg range of body mass (r2  =  0.87; P < 0.001), indicating the technique is remarkably robust among at least the 3 cervid species of our analysis. However, we found an underscoring bias with the rBCS for elk that had >12% body fat. This bias translated into a difference between subspecies, because Rocky Mountain elk tended to be fatter than Roosevelt elk in our sample. Effects of observer error with the rBCS also existed for mule deer with moderate to high levels of body fat, and deer body size significantly affected accuracy of the MAXFAT predictor. Our analyses confirm robustness of the rump-fat index for these 3 species but highlight the potential for bias due to differences in body size and to observer error with BCS scoring. We present alternative LIVINDEX equations where potential bias from rBCS and bias due to body size are eliminated or reduced. These modifications improve the accuracy of estimating body fat for projects intended to monitor nutritional status of herds or to evaluate nutritions influence on population demographics.

Validating Predictive Models of Nutritional Condition for Mule Deer

Abstract We developed new, and validated existing, indices of nutritional condition for live and dead mule deer (Odocoileus hemionus). Live animal indices included a body condition score (BCS), thickness of subcutaneous fat and selected muscles using ultrasonography, and body mass. Dead animal indices included femur, metatarsal, and mandible marrow fat, 3 kidney fat indices, and 2 carcass scoring methods. We used 21 female deer and 4 castrates (1–11 yr old) varying widely in nutritional condition (2–28% ingesta-free body fat). Deer were euthanized and homogenized for chemical analysis of fat, protein, water, and ash content. Estimates of fat and gross energy (GE) were regressed against each condition indicator using regression. Subcutaneous fat thickness, a rump BCS, and rLIVINDEX (an arithmetic combination of subcutaneous fat thickness and the rump BCS) were most related to condition for live animals (r2 ≥ 0.87, P < 0.001) whereas the Kistner score and kidney fat were most related to fat and GE for dead animals (r2 ≥ 0.77, P < 0.001). We also evaluated range of usefulness and sensitivity to small changes in body condition for all models. In general, indices with moderate or highly curvilinear statistical relations to body fat or those based on only one fat depot or a small number of ranking scores will have limitations in their use. Our results identify robust tools for a variety of research and monitoring designs useful for evaluating nutritions effect on mule deer populations.

Vegetative response to burning on Wyoming mountain-shrub big game ranges

Information on vegetative productivity and nutritive responses to burning in mesic, high elevation big sagebrush (Artemisia tridentata Nutt.) communities is limited. We investigated the effects of 2 wildfires and 3 prescribed fires on current years production of herbs and selected shrubs for 3 years post-burn, and forage quality for 2 years post-burn in high elevation big sagebrush habitats in southcentral Wyoming. Production of perennial herbs on burned sites averaged twice that on controls, while production of annual herbs varied little 2-3 years post-burn. Burn-induced mortality of Saskatoon serviceberry (Amelanchier alnifolia (Nutt) Nutt. ex Roem.) was less than or equal to 15%, but a 6-fold increase in twig production more than compensated for plant losses. Mortality of true mountain mahogany (Cercocarpus montanus Raf.) and antelope bitterbrush (Purshia tridentata (Pursh) DC) averaged 25% and 55%, respectively, but these losses generally were compensated by increases in browse production. Crude protein content of herbs from late spring through early far was significantly higher on burns for 2 years post-burn. These results suggest well-managed prescribed burning programs have potential to improve May through September diets of large herbivores in southcentral Wyoming mountain-shrub communities.

ONE-SAMPLE PREGNANCY DIAGNOSIS IN ELK USING FECAL STEROID METABOLITES

Recent research has demonstrated the potential of pregnancy diagnosis in elk (Cerlvus elaphus nelsoni) using immunoassays of fecal steroid concentration. However, multiple sampies are required to insure accurate results, limiting its utility for free-ranging animals. We attempted to develop an accurate one-sample pregnancy diagnosis using 153 fecal samples that were collected from free-ranging, radio-collared, adult female elk in Yellowstone National Park (Wyoming, USA) and from captive elk maintained at the Starkey Research Facility (La Grande, Oregon, USA) February through April 1992 and 1997. The pregnancy status of each animal was diagnosed using serum pregnancy-specific protein B (PSPB) assays providing fecal samples from 38 nonpregnant and 115 pregnant animals. Fecal radioimmunoassay (RIA) indicated that mean (± SD) progestagens (P4) were elevated significantly in pregnant (2.96 ± 1.49 μg/gm) compared to nonpregnant (0.43 ± 0.26 μ/gm) individuals. Confidence intervals (1.96 ± SE) for the two groups were widely separated (nonpregnant 0.34–0.51, pregnant 2.69–3.24) with little overlap in the range of concentrations measured for each group (nonpregnant 0.09–0.98, pregnant 0.90–8.29). These results indicate that fecal progestagens RIA provides a reliable method of noninvasive pregnancy diagnosis using single fecal samples collected from elk during late gestation. However, independent validation of the suggested discrimination criteria should be performed before routine application.