Peter Zager

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.

Neonatal mortality of elk driven by climate, predator phenology and predator community composition

1. Understanding the interaction among predators and between predation and climate is critical to understanding the mechanisms for compensatory mortality. We used data from 1999 radio-marked neonatal elk (Cervus elaphus) calves from 12 populations in the north-western United States to test for effects of predation on neonatal survival, and whether predation interacted with climate to render mortality compensatory. 2. Weibull survival models with a random effect for each population were fit as a function of the number of predator species in a community (3-5), seven indices of climatic variability, sex, birth date, birth weight, and all interactions between climate and predators. Cumulative incidence functions (CIF) were used to test whether the effects of individual species of predators were additive or compensatory. 3. Neonatal elk survival to 3 months declined following hotter previous summers and increased with higher May precipitation, especially in areas with wolves and/or grizzly bears. Mortality hazards were significantly lower in systems with only coyotes (Canis latrans), cougars (Puma concolor) and black bears (Ursus americanus) compared to higher mortality hazards experienced with gray wolves (Canis lupus) and grizzly bears (Ursus horribilis). 4. In systems with wolves and grizzly bears, mortality by cougars decreased, and predation by bears was the dominant cause of neonatal mortality. Only bear predation appeared additive and occurred earlier than other predators, which may render later mortality by other predators compensatory as calves age. Wolf predation was low and most likely a compensatory source of mortality for neonatal elk calves. 5. Functional redundancy and interspecific competition among predators may combine with the effects of climate on vulnerability to predation to drive compensatory mortality of neonatal elk calves. The exception was the evidence for additive bear predation. These results suggest that effects of predation by recovering wolves on neonatal elk survival, a contentious issue for management of elk populations, may be less important than the composition of the predator community. Future studies would benefit by synthesizing overwinter calf and adult-survival data sets, ideally from experimental studies, to test the roles of predation in annual compensatory and additive mortality of elk.

The role of American black bears and brown bears as predators on ungulates in North America

Abstract American black bears (Ursus americanus) and brown bears (U. arctos) can be important predators on neonatal ungulates. They prey less commonly on adult ungulates. Bear predation appears to be additive at low ungulate densities and may become compensatory as prey density approaches carrying capacity, K. As such, black and brown bear predation can limit, but generally does not regulate, ungulate populations. Maternal and neonatal physical condition, birth synchrony, and birth mass may predispose neonates to predation or other mortality factors. Though black and brown bear predation is an important proximate cause of ungulate neonatal mortality, habitat quality and quantity are important ultimate factors influencing this dynamic. Manipulating bear populations to enhance ungulate populations may be successful in the short-term if predation is additive, but long-term success has not been demonstrated.

Efficient, Noninvasive Genetic Sampling for Monitoring Reintroduced Wolves

Abstract Traditional methods of monitoring gray wolves (Canis lupus) are expensive and invasive and require extensive efforts to capture individual animals. Noninvasive genetic sampling (NGS) is an alternative method that can provide data to answer management questions and complement already-existing methods. In a 2-year study, we tested this approach for Idaho gray wolves in areas of known high and low wolf density. To focus sampling efforts across a large study area and increase our chances of detecting reproductive packs, we visited 964 areas with landscape characteristics similar to known wolf rendezvous sites. We collected scat or hair samples from 20% of sites and identified 122 wolves, using 8–9 microsatellite loci. We used the minimum count of wolves to accurately detect known differences in wolf density. Maximum likelihood and Bayesian single-session population estimators performed similarly and accurately estimated the population size, compared with a radiotelemetry population estimate, in both years, and an average of 1.7 captures per individual were necessary for achieving accurate population estimates. Subsampling scenarios revealed that both scat and hair samples were important for achieving accurate population estimates, but visiting 75% and 50% of the sites still gave reasonable estimates and reduced costs. Our research provides managers with an efficient and accurate method for monitoring high-density and low-density wolf populations in remote areas.

Demographic Response of Mule Deer to Experimental Reduction of Coyotes and Mountain Lions in Southeastern Idaho

ABSTRACT Manipulating predator populations is often posed as a solution to depressed ungulate populations. However, predator—prey dynamics are complex and the effect on prey populations is often an interaction of predator life history, climate, prey density, and habitat quality. The effect of predator removal on ungulate and, more specifically, mule deer (Odocoileus hemionus) populations has not been adequately investigated at a management scale. We tested the efficacy of removing coyotes (Cams latrans) and mountain lions (Puma concolor) for increasing survival and population growth rate of mule deer in southeastern Idaho, USA, during 1997–2003. We assigned 8 game management units (GMUs) to treatments under a 2 × 2 factorial design (treatments of coyote removal and lion removal) with 2 replicates of each treatment or reference area combination. We used methods typically available to wildlife managers to achieve predator removals and a combination of extensive and intensive monitoring in these 8 GMUs to test the hypothesis that predator removal increased vital rates and population growth rate of mule deer. We determined effects of predator removal on survival and causes of mortality in 2 intensive study sites, one with coyote and mountain lion removal and one without. We also considered the effects of other variables on survival including lagomorph abundance and climatic conditions. In these 2 intensive study areas, we monitored with radiotelemetry 250 neonates, 284 6-month-old fawns, and 521 adult females. At the extensive scale, we monitored mule deer population trend and December fawn ratios with helicopter surveys. Coyote removal decreased neonate mortality only when deer were apparently needed as alternate prey, thus removal was more effective when lagomorph populations were reduced. The best mortality model of mule deer captured at 6 months of age included summer precipitation, winter precipitation, fawn mass, and mountain lion removal. Over-winter mortality of adult female mule deer decreased with removal of mountain lions. Precipitation variables were included in most competing mortality models for all age classes of mule deer. Mountain lion removal increased fawn ratios and our models predicted fawn ratios would increase 6% at average removal rates (3.53/1,000 km2) and 27% at maximum removal rates (14.18/1,000 km). Across our extensive set of 8 GMUs, coyote removal had no effect on December fawn ratios. We also detected no strong effect of coyote or mountain lion removal alone on mule deer population trend; the best population-growth-rate model included previous years mountain lion removal and winter severity, yet explained only 27% of the variance in population growth rate. Winter severity in the current and previous winter was the most important influence on mule deer population growth. The lack of response in fawn ratio or mule deer abundance to coyote reduction at this extensive (landscape) scale suggests that decreased neonate mortality due to coyote removal is partially compensatory. Annual removal of coyotes was not an effective method to increase mule deer populations in Idaho because coyote removal increased radiocollared neonate fawn survival only under particular combinations of prey densities and weather conditions, and the increase did not result in population growth. Coyote-removal programs targeted in areas where mortality of mule deer fawns is known to be additive and coyote-removal conditions are successful may influence mule deer population vital rates but likely will not change direction of population trend. Although mountain lion removal increased mule-deer survival and fawn ratios, we were unable to demonstrate significant changes in population trend with mountain lion removal. In conclusion, benefits of predator removal appear to be marginal and short term in southeastern Idaho and likely will not appreciably change long-term dynamics of mule deer populations in the intermountain west.

Predicting white-tailed deer habitat use in Northern Idaho

Winter habitat use patterns of white-tailed deer (Odocoileus virginianus) have been studied extensively across their northern distribution. However, previous research has contributed little to predicting habitat use of unstudied populations. Thus, we evaluated winter habitat use of white-tailed deer in the Priest River drainage of northern Idaho and developed a predictive model of winter habitat selection. Our findings suggest that winter habitat selection is predictable given seasonal changes in basal metabolism and the effects of snow accumulation on forage availability and energy expenditure. During early (18 Nov-8 Jan) and late (3 Mar-2 Apr) winter, when basal metabolic rates were elevated and snow depths did not exceed 30 cm, white-tailed deer selected lodgepole pine (Pinus contorta) and Douglas-fir (Pseudotsuga menziesii) pole timber stands that provided the greatest availability of preferred forage species

Statistical models for population reconstruction using age-at-harvest data

Statistical analyses based on maximum likelihood methods are presented to jointly estimate harvest rates, survival, recruitment, and population abundance from age-at-harvest data. To perform the population reconstruction from the age-at-harvest data, auxiliary field data and information on harvest reporting rates are required. The statistical methods permit tests of model assumptions, goodness-of-fit, and standard errors and confidence intervals for all estimated demographic parameters. We illustrate the methods using harvest data and radiotelemetry studies of elk (Cervus elaphus) from northern Idaho, USA, 1988-1993. We compare results with abundance estimates using an aerial sightability survey on the same herd. The maximum likelihood methods for age-at-harvest analysis provide a comprehensive framework for population reconstruction with abundance estimates comparable to field survey techniques.

Detection of Predator Presence at Elk Mortality Sites Using mtDNA Analysis of Hair and Scat Samples

Abstract The identification of carnivores responsible for preying on wild or domestic ungulates often is of interest to wildlife managers. Typically, field personnel collect a variety of data at mortality sites including scat or hair samples that may have been deposited by the predator. We compared mitochondrial DNA (mtDNA) analysis of hair and scat samples (n = 122) collected at elk (Cervus elaphus) mortality sites between 1997 and 2004 in north-central Idaho, USA, with field identification of carnivore presence. We amplified mtDNA from samples via a 2-step process involving an initial screening for American black bears (Ursus americanus), brown bears (Ursus arctos), and gray wolves (Canis lupus) using a length variation in the 5′ hypervariable section of the control region. Samples that failed the first screening subsequently were analyzed using conserved mtDNA primers that amplify a wide array of vertebrates. Species identification success rate was high (88.5%) and established the presence of 3 predators at elk mortality sites including black bears (55.7%), cougars (Puma concolor; 27.9%), and coyotes (Canis latrans; 6.6%). Attempts at hair and scat identification by field personnel were correct for 58% of hair samples and 79% of fecal samples. Results from these analyses demonstrate the merits of combining field mortality assessments with mtDNA species identification to aid wildlife managers in more accurately pinpointing predators involved in either predation or depredation events.

Population dynamics of Selkirk Mountains Grizzly bears

We investigated population dynamics of grizzly bears (Ursus arctos) in the Selkirk Mountains Grizzly Bear Ecosystem (SMGBE) of Idaho, Washington, and British Columbia to assist grizzly bear recovery from threatened status. We captured and radiomonitored 28 bears from 1985 to 1990. Estimated densities were 1.41 ± 0.14 (95 % CL) and 2.33 ± 0.36 bears/100 km 2 for the U.S. and Canadian portions of the SMGBE, respectively. Litter size (cubs ≤ 1.5 yr) was 2.22 ± 0.26 and mean birth interval was 3.0 ± 0.5 years for an estimated reproductive rate of 0.74 ± 0.10 cubs/adult female per year. Age at first parturition was 7.3 ± 0.38 years. Estimated annual survival rates were 0.96 ± 0.05 for adult females, 0.81 ± 0.20 for adult males, 0.78 ± 0.22 for subadult females, 0.90 ± 0.17 for subadult males, and 0.84 ± 0.16 for cubs

Relative influence of human harvest, carnivores, and weather on adult female elk survival across western North America

Summary 1. Well-informed management of harvested species requires understanding how changing ecological conditions affect demography and population dynamics, information that is lacking for many species. We have limited understanding of the relative influence of carnivores, harvest, weather and forage availability on elk Cervus elaphus demography, despite the ecological and economic importance of this species. We assessed adult female survival, a key vital rate for population dynamics, from 2746 radio-collared elk in 45 populations across western North America that experience wide variation in carnivore assemblage, harvest, weather and habitat conditions. 2. Proportional hazard analysis revealed that ‘baseline’ (i.e. not related to human factors) mortality was higher with very high winter precipitation, particularly in populations sympatric with wolves Canis lupus. Mortality may increase via nutritional stress and heightened vulnerability to predation in snowy winters. Baseline mortality was unrelated to puma Puma concolor presence, forest cover or summer forage productivity. 3. Cause-specific mortality analyses showed that wolves and all carnivore species combined had additive effects on baseline elk mortality, but only reduced survival by <2%. When human factors were included, ‘total’ adult mortality was solely related to harvest; the influence of native carnivores was compensatory. Annual total mortality rates were lowest in populations sympatric with both pumas and wolves because managers reduced female harvest in areas with abundant or diverse carnivores.