P. J. White

Northern Yellowstone elk after wolf restoration

Abstract We analyzed counts, vital rates, and limiting factors for northern Yellowstone elk (Cervus elaphus) before and after wolf (Canis lupus) restoration in 1995–1996 to evaluate predictions that elk numbers would move to a lower equilibrium point with corresponding density-related changes in vital rates. Elk counts decreased from approximately 17,000 in 1995 to 8,335 in 2004. Pregnancy rates for prime-age females (3–15 years) during 2000–2003 were high (0.90) and similar to those during 1950–1967 when elk density was 30% lower (5–9 elk/km2). The survival rate for prime-aged females was 0.85 (95% CI = 0.81–0.87) compared to 0.99 when harvests were low and wolves absent. The proportions of elk harvested each year increased as elk numbers decreased during 1990–2002 but departed from this anti-regulatory trend as permit levels were reduced in 2003–2004. Snow pack strongly influenced elk vulnerability to hunting by increasing migration to lower elevations. Thus, harvests removed a relatively constant proportion (27±5%) of animals that migrated out of the park each year, primarily prime-aged females with high reproductive value. Conservative estimates of wolf off-take (>1,000 elk) exceeded harvests by 2003, with wolves primarily selecting calves and older elk with lower reproductive value. Recruitment decreased as the ratio of wolves to elk increased, and wolves maintained high kill rates and rapid population growth despite a 50% decrease in elk counts. Elk numbers likely will continue to decrease until 1) levels of harvest and predation decrease sufficiently, 2) there is sufficient time for recruitment of calves to prime breeding age, and 3) there is a numerical response of wolves to fewer elk. We recommend that managers quickly adjust antlerless permit quotas to population size in a density-dependent manner so that harvests do not accelerate the decrease in elk numbers.

A Seventy-Year History of Trends in Yellowstone's Northern Elk Herd

Abstract We analyzed counts of northern Yellowstone elk (Cervus elaphus) in Yellowstone National Park, Wyoming, USA, over 70 years to evaluate the effects of changing management on population trends. Population reduction efforts and hunter harvests during 1932–1968 removed 71,330 elk and decreased estimated abundance from 16,000 to 6,000 elk. Abundance increased to approximately 17,000 elk (λ = 1.19) when removals ceased and harvests were very small during 1969–1975. Moderate to liberal hunter harvests of antlerless elk outside the Park during 1976–2004 removed a relatively consistent proportion (26 ± 0.1 [SD]%) of females that migrated outside the park, mostly from prime-age (3–15 yr) classes with high reproductive value. Substantial winterkill was infrequent (1989, 1997), but it significantly reduced calf survival when it occurred. Wolves (Canis lupus) were reintroduced in 1995–1996 and rapidly increased in abundance (λ = 1.23) and distribution. Estimated wolf kill of elk now exceeds hunter harvest, but has a smaller effect on population dynamics because wolves concentrate on calves and older females (>14 yr) with low reproductive value. During 1995–2004, estimated abundance decreased from 23,000 to 12,000 elk. The recent ratio of wolves to elk is relatively low compared to the estimated equilibrium ratio, suggesting that the wolf population may yet increase in the future. Thus, reduction of harvests of prime-aged female elk to decrease removals of animals with high reproductive value and increase adult female survival appears essential. We analyzed the relative impact of removals by hunters and by wolves using Fishers (1930) reproductive value and found that the impact of hunters is far more important than that by wolves, a finding of broad significance.

Functional and numerical responses of kit foxes to a short-term decline in mammalian prey

Diet and abundance of San Joaquin kit foxes ( Vulpes macrotis mutica ) were monitored over 45 months (1989–1992) at a semi-arid site in southcentral California. From 1990 to early 1991, the mammalian prey of these endangered foxes declined markedly to densities 2–5 × lower than at peak. During late 1991 and 1992, however, the populations of at least three species of mammalian prey irrupted. Regardless of these fluctuations, foxes maintained consistent preferences among small mammals, and did not shift their diets to other prey when mammalian prey was scarce. Although we did not detect a clear functional response, foxes did respond numerically because their abundance decreased after the decline in mammalian prey. This decline in abundance was due to proportionately fewer females successfully rearing young and high coyote-induced mortality, rather than foxes abandoning their territories. Because kit foxes continue to prey on their staple species during times of prey scarcity, declines in rates of consumption could exert a strong influence on the population dynamics of this endangered fox. We suggest that population dynamics of kit foxes may be similar to those of obligate predators due to their apparent unwillingness or inability to switch to abundant, alternate prey during declines in density of their preferred prey.

Generalizing wolf effects across the Greater Yellowstone Area: a cautionary note

Abstract Although numerous authors are investigating indirect effects of wolf recovery, the most fundamental ecological impact of the Greater Yellowstone Area wolf reintroduction, the effects of wolf predation on ungulate populations, remains unclear. We report on a 5-year comparative study of wolf (Canis lupus)–elk (Cervus elaphus) dynamics on an elk herd in the headwaters of the Madison River within Yellowstone National Park and the lower Madison elk herd that winters 40 km downriver outside the Park. A resident pack became established on the Madison headwaters area in 1997 and grew to multiple packs totaling 30–40 animals by 2002. During winter 1999 emigrates from Yellowstone established a pack on the lower Madison area. However, poor recruitment and low adult survival limited wolf population growth, with the area supporting a single pack, never exceeding 5 animals. Wolf kill rates on the lower Madison area were approximately double that documented for the Madison headwaters area. Moderate kill rates in the Madison headwaters, combined with high wolf densities and modest elk densities, resulted in an estimated 20% of the elk population being killed during winter and projections for a declining elk population. In contrast, high kill rates on the lower Madison area, combined with low wolf densities and high elk densities, resulted in winter predation estimates not exceeding 4% of the elk population. We suspect this level of mortality will be of little biological significance with respect to elk population trajectory. These results suggest that the effects of wolf predation on elk populations differ substantially over relatively small spatial scales, depending on a complex suite of interacting factors. Thus, we caution against generalizing the effects of wolf restoration on elk dynamics from any single study and encourage collaborations to develop comparative predator–prey studies that improve our understanding of wolf–ungulate interactions and enhance conservation.

ASSESSING THE IMPACT OF WOLVES ON UNGULATE PREY

Simple models may be useful in evaluating definitions of population limitation and regulation, and in considering the impact of wolves (Canis lupus) on ungulate prey. Examination of three types of models that have recently been used to assess wolf–ungulate interactions indicates that the “total response” model is inappropriate and that models generating substantial oscillations may not be realistic. Models based on ratio dependence appear to be more useful and are explored further. Because reintroduction of wolves into areas with abundant prey may yield new insights into the controversial issue of population regulation by predators, the available data are used to consider some needs for research on the impact of wolves on Yellowstone elk (Cervus elaphus) herds, and for a further assessment of ratio dependence. n nCorresponding Editor: F. C. James

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.

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.

DIAGNOSING PREGNANCY IN FREE-RANGING ELK USING FECAL STEROID METABOLITES

We validated fecal metabolite analysis as a noninvasive means of diagnosing pregnancy in uncaptured, free-ranging Rocky Mountain elk (Cervus elaphus nelsoni). During November 1991, we collected blood samples from 21 radiocollared, 1- to 10-year-old female elk in Yellowstone National Park, Wyoming (USA), and determined their pregnancy status by radioimmunoassay of serum pregnancy specific protein B and serum progesterone concentrations. From December 1991 through April 1992, we collected three to 12 fecal samples from each collared elk and measured the concentration of estrone conjugates, pregnanediol-3-glucuronide, and free progesterone by enzyme immunoassays. We also evaluated fecal samples from 10 unmarked male and eight calf elk. Pregnant females had significantly (P < 0.001) higher concentrations of all three fecal metabolites than nonpregnant animals, especially later in gestation (March to April). We developed all possible combinations of univariate, bivariate, and multivariate discriminant function analysis models to determine those variables most useful in predicting memberships of pregnant versus nonpregnant elk during the March to April time-period. We validated each model by applying the classification functions to 11 pregnant and eight nonpregnant elk that were not included in the development of the original models. Accuracy of the discriminant function analysis models ranged from 57 to 84%, with the univariate model based on pregnanediol-3-glucuronide concentration providing the highest classification. Fecal metabolite analysis will enable biologists to noninvasively assess the pregnancy status of elk, especially when diagnoses are based upon multiple samples collected between mid-March and mid-April.

Purine derivatives in snow-urine as a dietary index for free-ranging elk

Vagnoni et al. (1996) performed experiments with captive elk (Cervus elaphus) that demonstrated a correlation between excretion of the purine derivative allantoin in urine and intake of digestible dry matter, suggesting urinary purine derivatives may be potential dietary indices for wild ruminants. To further explore the potential of urinary purine derivatives we collected sequential snow-urine samples from 5 free-ranging radiocollared cow elk in Yellowstone National Park (NP) during the winters of 1991-92, 1992-93, and 1993-94. A total of 116 snow-urine samples were assayed to determine concentrations of creatinine and allantoin, with 72 of the samples also assayed for other purine derivatives. Allantoin consistently accounted for >70% (x = 80.3%, SD = 8.7%) of total urinary purine derivatives and was correlated with other purine derivatives, indicating that measurement of allantoin adequately indexed total urinary purine derivative concentration. Allantoin: creatinine ratios (A: C) were calculated as an index of digestible dry matter intake, with creatinine standardizing allantoin concentration for differences in hydration and body size among animals, and the dilution effects of snow. The seasonal patterns in In(A:C) ratios followed the predicted U-shaped pattern, with lowest values occurring in midwinter and significantly higher values in December and April (P ≤ 0.001). This seasonal pattern generally remained consistent among winters despite substantial differences in mean annual In(A: C) values among all 3 winters. The lowest annual values were recorded for the winter of 1992-93 and the highest for the winter of 1993-94. Annual differences in A:C ratios corresponded with annual variations in winter severity, as indexed by measurements of snowpack and decreases in calf:cow ratios each winter. The results of this exploratory study suggest that urinary A: C ratios derived from snow-urine samples may be a useful noninvasive dietary index for free-ranging ruminants. Additional research, however, will be required to fully assess its utility.

Urinary allantoin : Creatinine ratios as a dietary index for elk

This study was conducted to evaluate the relation between digestible dry matter intake (DDMI) and urinary allantoin:creatinine (A:C) ratios in elk. The experiment was conducted from August 1993 through March 1994 and involved 18, 2-year-old cow elk divided into 3 groups of 6 animals each. Groups were randomly assigned to 1 of 3 dietary treatments involving mixtures of alfalfa hay and pelleted rations providing digestible dry matter intakes ranging from 1.2 to 4.0 kg/day. Animals were weighed twice weekly and urine samples were collected from each animal at about 3-week intervals throughout the experiment for a total of 10 samples per animal. Animals fed an ad libitum diet gained an average of 6.8% of their initial body mass (BM), while elk on 2 restricted dietary treatments lost an average of 9.3 and 11.2% of their initial BM over the course of the experiment. A significant (P < 0.001) curvilinear relation between urinary A:C ratios and DDMI, consistent with observations with domestic ruminants, was detected. These results suggest that urinary A:C ratios may provide a useful diagnostic tool to study the DDMI of free-ranging elk.