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The controversy ( Berger 1990, 1999; Wehausen 1999) over rapid extinction in bighorn sheep (Ovis canadensis) has focused on population size alone as a correlate to persistence time. We report on the persistence and population performance of 24 translocated populations of bighorn sheep. Persistence in these sheep was strongly correlated with larger patch sizes, greater distance to domestic sheep, higher population growth rates, and migratory movements, as well as to larger population sizes. Persistence was also positively correlated with larger average home-range size (p = 0.058, n = 10 translocated populations) and home-range size of rams (p = 0.087, n = 8 translocated populations). Greater home-range size and dispersal rates of bighorn sheep were positively correlated to larger patches. We conclude that patch size and thus habitat carrying capacity, not population size per se, is the primary correlate to both population performance and persistence. Because habitat carrying capacity defines the upper limit to population size, clearly the amount of suitable habitat in a patch is ultimately linked to population size. Larger populations (250+ animals) were more likely to recover rapidly to their pre-epizootic survey number following an epizootic (p = 0.019), although the proportion of the population dying in the epizootic also influenced the probability of recovery (p = 0.001). Expensive management efforts to restore or increase bighorn sheep populations should focus on large habitat patches located ≥23 km from domestic sheep, and less effort should be expended on populations in isolated, small patches of habitat. Resumen: La controversia ( Berger 1990, 1999, Wehausen 1999) sobre extinciones rapidas del borrego cimarron (Ovis canadiensis) se ha enfocado solo en los tamanos poblacionales como una correlacion con los tiempos de persistencia. Reportamos la persistencia y adaptabilidad de 24 poblaciones translocadas de cimarrones. La persistencia de estos borregos cimarrones estuvo fuertemente correlacionada con parches de tamano grande, distancias grandes con los borregos domesticos, tasas de crecimiento poblacional elevadas, movimientos migratorios, y con tamanos poblacionales grandes. La persistencia tambien estuvo positivamente correlacionada con un tamano de rango de hogar promedio grande (p = 0.058, n = 10 poblaciones translocadas) y el tamano del rango de hogar de los cimarrones (p = 0.087, n = 8 poblaciones translocadas). Un mayor tamano en el rango de hogar y mayores tasas de dispersion estuvieron positivamente correlacionadas con parches grandes. Por lo tanto concluimos que el tamano del parche y la capacidad de carga del habitat, pero no el tamano poblacional, en si, es la correlacion principal tanto para la adaptabilidad como para la persistencia de la poblacion. Debido a que la capacidad de carga del habitat define los limites superiores del tamano poblacional, es claro que la cantidad de habitat propicio en un parche esta en ultima instancia ligada al tamano poblacional. Las poblaciones mas grandes (250+ animales) tuvieron mas factibilidad de recuperacion de sus n muestreados pre-epizooticos despues de una epizootia (p = 0.019), aunque la proporcion de la poblacion que estaba falleciendo durante el evento epizootico tambien influencio la probabilidad de recuperacion (p = 0.001). Los costosos esfuerzos de restauracion o incremento de poblaciones de borrego cimarron deberian ser canalizados hacia parches grandes que se encuentran a mas de 23 km de las ovejas domesticas, y se deberian canalizar menos esfuerzos hacia poblaciones que se encuentren en parches de habitat aislados y pequenos.

Prey species are thought to select habitats to obtain necessary resources while also avoiding predation. We examined whether habitat selection by elk (Cervus elaphus) changed following the reintroduction of wolves (Canis lupus) into Yellowstone National Park in 1995. Using conditional fixed-effects logistic regression to build habitat-selection models, we compared seasonal habitat selection by elk based on weekly elk radiolocations taken in 1985–1990 (without wolves) and 2000–2002 (with wolves). Fire-related habitat changes and climate likely interacted with wolf avoidance in shaping habitat selection by elk. In summer, when wolf activity was centered around dens and rendezvous sites, elk apparently avoided wolves by selecting higher elevations, less open habitat, more burned forest, and, in areas of high wolf density, steeper slopes than they had before wolf reintroduction. In winter, elk did not spatially separate themselves from wolves. Compared to the pre-wolf period, elk selected more open h...

We used 35-year and 4-year ungulate exclosures to determine the effects of elk (Cervus elaphus) herbivory on above-ground and below-ground production and soil fertility on the elk winter range in Rocky Mountain National Park (RMNP), Colorado, USA. We used paired grazed and ungrazed plots to evaluate ungulate herbivory effects in short and tall willow (Salix spp.), aspen (Populus spp.), and upland grass/shrub vegetation associations. We measured nitrogen (N) fluxes (litter deposition, fecal and urinary deposition from elk, movements of N by elk, N mineralization, soil N availability, elk consumption rates) within the elk winter, above-ground and below-ground N pools (herbaceous, shrub and root biomass, %N in plants, roots, and soil), and N fluxes on and off the elk winter range (seasonal movement of N by elk). Nitrogen mineralization and soil nitrate (NO3) pools were reduced in the short willow community (P = 0.07 and 0.10, respectively; n = 4 sites) in grazed plots, but not in the upland grass/sh...

We used three 35-year exclosures to examine the effects of high elk populations on a variety of soil properties in three vegetation types: upland sagebrush, aspen, and meadow. Grazing and hoof action by elk significantly increased bulk density (from 0.87 kg/l ungrazed to 0.94 kg/l grazed), with greater effects on soils with fewer rocks. Grazing substantially reduced extractable calcium, magnesium, potassium and phosphorus in the sagebrush type, but not in the aspen or meadow types. The only grazing effect on pH came in aspen types, where grazing prevented aspen establishment, and kept soil pH about 0.7 units higher than under aspen inside the exclosures. Grazing had no overall effect on total soil C and N across all exclosures and vegetation types. The availability of soil nitrogen, indexed by in-field resin bags and net mineralization in soil cores, showed little overall effect of grazing. Limited data on soil leaching indicated a possibility of strong increases in nitrate leaching with grazing for an aspen vegetation type at one exclosure. Although we found little effect of grazing on soil N supply, we note that N fertilization doubled the production of grasses and shrubs; if grazing eventually led to changes in soil N supply, species composition and growth would likely change.

Nitrogen (N) is an essential nutrient for plants and animals, and N may be limiting in many western US grassland and shrubland ungulate winter ranges. Ungulates may influence N pools and they may alter N inputs and outputs (losses) to the ecosystem in a number of ways. In this paper we compare the ecosystem effects of ungulate herbivory in two western national parks, Rocky Mountain National Park (RMNP), Colorado, and Yellowstone National Park (YNP), Wyoming. We compare ungulate herbivory effects on N pools, N fluxes, N yields, and plant productivity in the context of the accelerating and decelerating nutrient cycling scenarios [Ecology 79 (1998) 165]. We concluded that the YNP grasslands fit the accelerating nutrient cycling scenario for ungulate herbivory: in response to grazing, grassland plant species abundance was largely unaltered, net annual aboveground primary productivity (NAPP) was stimulated (except during drought), consumption of key N-rich forages by ungulates was moderate and their abundance was sustained, soil N mineralization rates doubled, N pools increased, aboveground N yield increased, and N concentrations increased in most grassland plant species. Grazing in grasslands in RMNP resulted in no consistent detectable acceleration or deceleration of nutrient cycling. Grazing effects in short willow and aspen vegetation types in RMNP fit the decelerating nutrient cycling scenario of Ritchie et al. [Ecology 79 (1998) 165]. Key N-rich forages declined due to herbivory (willows, aspen, herbaceous vegetation). Aboveground production declined, soil N mineralization rates declined, N pools declined (NO3− pools were 30% that of ungrazed controls), and aboveground N yield declined. We believe that the higher ungulate densities and rates of plant consumption in RMNP, large declines in N-rich forage plants, and possibly a tendency of ungulates to move N from willow and aspen vegetation types to other types in RMNP, contributed to deceleration of nutrient cycling in two vegetation types in RMNP compared to acceleration in grasslands in YNP.

Changing climate may impact wildlife populations in national parks and conservation areas. We used logistic and non-linear matrix population models and 35 years of historic weather and population data to investigate the effects of climate on the population dynamics of elk in Rocky Mountain National Park (RMNP), Colorado, U.S.A. We then used climate scenarios derived from Hadley and Canadian Climate Center (CCC) global climate models to project the potential impact of future climate on the elk population. All models revealed density-dependent effects of population size on growth rates. The best approximating logistic population model suggested that high levels of summer precipitation accelerated elk population growth, but higher summer minimum temperatures slowed growth. The best approximating non-linear matrix model indicated that high mean winter minimum temperatures enhanced recruitment of juveniles, while high summer precipitation enhanced the survival of calves. Warmer winters and wetter summers predicted by the Hadley Model could increase the equilibrium population size of elk by about 100%. Warmer winters and drier summers predicted by the CCC Model couldraise the equilibrium population size of elk by about 50%. Managers of national parks have relied on effects of weather, particularly severe winters, to regulate populations of native ungulates and prevent harmful effects of overabundance. Our results suggest that these regulating effects of severe winter weather may weaken if climate changes occur as those that are widely predicted in most climate change scenarios.

Translocation of bighorn sheep (Ovis canadensis) is time, labor, and cost intensive and, therefore, high levels of success are desirable. We tested a widely used habitat suitability model against translocation success and then modified it to include additional factors which improved its usefulness in predicting appropriate translocation sites. The modified Smith habitat suitability model for bighorn sheep was 64% accurate in predicting success or failure of 32 translocations of bighorn sheep into the Rocky Mountains, Colorado Plateau desert, and prairie-badlands of six states. We had sheep location data for 13 populations, and the modified habitat model predicted the areas used by bighorn sheep with greater than 90% accuracy in eight populations, greater than 55% accuracy in four populations, and less than 55% accuracy in one population. Translocations were more successful when sheep were placed into discrete habitat patches containing a high proportion of lambing period habitat (>10% of suitable habitat, p = 0.05), where animals had a migratory tendency ( p = 0.02), no contact with domestic sheep ( p = 0.02), or greater distance to domestic sheep (>23 km, p = 0.02). Rate of population growth was best predicted by area of lambing period habitat, potential area of winter range, and distance to domestic sheep. We retested the model using these refined criteria and the refined model then predicted success or failure of these 32 translocated populations with 82% accuracy.

Bighorn sheep (Ovis canadensis) once were ubiquitous in large areas, including lands now contained in the national parks of the Intermountain and Colorado Plateau regions of the United States. Due to catastrophic declines in the late 1800s and early 1900s, most extant populations now occur as small, isolated groups with a highly fragmented distribution. Three different subspecies of bighorn sheep were extirpated from 14 of 18 areas that are now managed by the National Park Service. We describe an eight-year plan to restore bighorn sheep to currently suitable historic habitats in the national parks within a six-state intermountain region of the western United States, 1991-1998. A seven-point program was recommended for each park unit that included: (1) survey the existing populations; (2) conduct a GIS-based habitat assessment to identify suitable habitat; (3) convene scientific advisory panels to review results of habitat assessment; (4) convene interagency panels to discuss metapopulation management and to plan the restoration(s); (5) draft interagency restoration and management plans; (6) conduct translocation(s); and (7) monitor the populations. We evaluated 38,781 km 2 of area; 32% (12,329 km 2 ) was potential habitat for bighorn sheep. The scientific advisory panels and the GIS modeling recommended bighorn restoration on 73 sites within these areas. By 1996, 36 of these sites (2,647 km 2 or 22% of the entire suitable area) were inhabited by bighorn sheep. By 1999, the translocated animals increased 25%, and restoration efforts will continue in many of the remaining sites.

We analyzed factors that contributed to the success of 100 translocations of bighorn sheep within six western states between 1923 and 1997. We categorized the populations as unsuccessful (i.e., extirpated or remnant, , 29 animals), moderately successful (30‐99 animals), and successful (100‐350 animals) by the end of the study period in 1997. Thirty of the translocated populations were unsuccessful ( n 5 13 were extirpated and n 5 17 were remnant), 29 were moderately successful, and 41 were successful (21 6 1.3 [SE] years of information per translocation). Translocations were less successful when domestic sheep were located within 6 km of the known bighorn sheep use areas (logistic regression, p 5 0.052). Grazing of cattle on the same range also negatively influenced success ( p 5 0.004). Use of indigenous versus previously translocated source stocks increased success ( p 5 0.084). The translocation was twice as likely to be successful when indigenous herds were used as sources ( p 5 0.043), but mixing genetic stocks ( p 5 0.381) or later additional augmentations did not influence success ( p 5 0.095). Annual migrations by newly established translocated populations increased success ( p 5 0.014). We recommend translocations of founder groups of bighorn sheep from indigenous

We simulated population dynamics of bighorn sheep (Ovis canadensis) inhabiting six discrete habitat patches in the Badlands ecosystem, South Dakota. Modeled populations were subjected to a range of potential management actions and rates of disease-causing infection. Simulated disease varied in severity from mild (∼12% mortality) to severe (∼67% mortality), with infections imposed once, at regular intervals, or with a fixed probability each year. In the absence of disease, 200-year extinction rates were uniformly low and insensitive to changes in colonization rate or area of suitable habitat. A single infection, accompanied by change in the area of suitable habitat or colonization rate, resulted in extinction rates of up to 40%, and large changes in average population size (up to 10-fold with changes in area; 4-fold with changes in colonization rate). Simulations with multiple infections, which are probably most realistic, generally resulted in extinction rates that exceeded 20% over a 200-year period. Model results clearly showed that efforts directed toward reducing the frequency or severity of disease are of highest priority for improving the success of attempts to restore bighorn sheep populations. Increases in areas of suitable habitat or improvements to corridors between existing habitat patches were far less likely to improve persistence of simulated sheep populations than reductions in the impact of disease. Although theory predicts that enhanced movements may exacerbate effects of disease, increased colonization rates resulted in relatively small but consistent increases in persistence and average population size for all combinations of parameters we examined.

The single greatest obstacle to the restoration of large, healthy, populations of bighorn sheep (Ovis canadensis) in the western United States is epizootic outbreaks of bronchopneumonia that may kill 20-100% of the animals in populations. Although the species is capable of rapid initial growth rates following restoration into new habitat (λ = 1.23-1.30 have been observed), these rates of increase are typical only a few years following the release of a population, and then most populations either decline to extirpation or remnant status (

By 1950, bighorn sheep were extirpated from large areas of their range. Most extant populations of bighorn sheep (Ovis canadensis) in the Intermountain West consist of

The elk and bison winter ranges in the Jackson Valley lie on a land complex consisting of Grand Teton NP (GTNP), National Elk Refuge (NER), town of Jackson, private ranches, and private housing developments. To reduce conflicts on these private lands, elk and bison are artificially fed alfalfa pellets at several feedgrounds located on the National Elk Refuge, the Gros Ventre Valley (Bridger-Teton NF), and south of the town. The concentrations of elk may be altering vegetation communities, especially riparian willow, aspen, buffaloberry, and other woody shrubs near the feedgrounds. Managers are concerned about these possible alterations. Human developments, human alterations, artificial feeding and high incidence of brucellosis in elk and bison complicate management of free-ranging ungulates in Grand Teton NP and the Jackson Valley. Managers need additional information on predicted land use changes, feeding scenarios, and ungulate-disease relations in the Jackson Valley to guide their management decisions.

The interrelations of weather, plant production and abundance, and elk pop- ulation dynamics on Yellowstone's northern winter range were examined for a 23-yr period when there was minimal human offtake from the herd. Significant correlations between precipitation and plant production, between elk population responses and precipitation, and between elk population responses and elk population density strongly suggested that forage limited elk population growth. Although population responses to density have been doc- umented previously in Yellowstone, responses to precipitation have not. Correlations be- tween elk population responses and annual precipitation were presumably consequences of plant growth responses to precipitation and subsequent effects on elk nutritional status. Population regulation was most consistently achieved through the responses of juveniles rather than adults. Winter mortality of juveniles was primarily correlated with elk numbers, whereas recruitment was primarily correlated with precipitation. Adult mortality rates were not significantly correlated with elk numbers, but were correlated with precipitation. Per capita rate of increase was negatively correlated with elk number, but 55% of the variance was density-independent. There was evidence that winter weather affected the elk, but season-long weather indices had poor predictive power. A stage-structured population model using regression equations of mortality and recruitment rate responses to precipitation and elk numbers, predicted that the population could vary within a range of -16400 ? 2500 sighted elk (mean ? 1 SD).

Niche relationships and diet overlaps were compared among elk (Cervus elaphus), bison (Bison bison), bighorn sheep (Ovis canadensis), mule deer (Odocoileus hemionus), and pronghorn antelope (Antilocapra americana) between 1967–1970 and 1986–1988, a period when total ungulate numbers nearly tripled on Yellowstone's northern range. Ungulate species ratios on Yellowstone's northern winter range during the latter period were 100 elk : 10 mule deer : 3 bison : 2 pronghorns : 1 bighorns. Elk numbers were positively correlated to bison, mule deer, and pronghorn numbers (r2 = 0.76, 0.97, and 0.48, respectively, P

In three sampling areas (two unhunted, one hunted), we compared activity patterns of Dall sheep rams (Ovis dalli) of different horn size during the rut. In all three areas rams with horns 3 4 - curled and smaller rams were less frequently seen in ewe bands as the rut progressed. In one area where we documented activity budgets, we observed equivalent budgets for ewes and rams with horns 1 4 - curled . Older rams spent less time foraging than young rams, except that rams with horns 5 8 – 7 8 curled spent less time foraging than full-curl rams late in the rut. Display frequencies of 7 8 - curl rams were similar to those of full-curl rams and considerably higher than those of smaller-horned rams early in the rut. These results suggest that the rut is more energy costly for old rams than for young rams, but that it may be most costly for the next-to-largest horn-curl class rams (e.g. 7 8 - curl rams in unhunted populations) rather than the dominant rams (full-curl and larger). Rams in the next-to-largest horn-curl class in the hunted herd, however, did not acquire the higher display rates (e.g., 3 4 - curl rams had equally low display rates in both the hunted and unhunted herds).

Lack of aspen (Populus tremuloides) recruitment and canopy replacement of aspen stands that grow on the edges of grasslands on the low-elevation elk (Cervus elaphus) winter range of Rocky Mountain National Park (RMNP) in Colorado has been a cause of concern for more than 70 years (Packard, 1942; Olmsted, 1979; Stevens, 1980; Hess, 1993; R.J. Monello, T.L. Johnson, and R.G. Wright, Rocky Mountain National Park, 2006, written commun.). These aspen stands are a significant resource since they are located close to the park's road system and thus are highly visible to park visitors. Aspen communities are integral to the ecological structure of montane and subalpine landscapes because they contain high native species richness of plants, birds, and butterflies (Chong and others, 2001; Simonson and others, 2001; Chong and Stohlgren, 2007). These low-elevation, winter range stands also represent a unique component of the park's plant community diversity since most (more than 95 percent) of the park's aspen stands grow in coniferous forest, often on sheltered slopes and at higher elevations, while these winter range stands are situated on the low-elevation ecotone between the winter range grasslands and some of the park's drier coniferous forests.

International audience; Using the example of a reintroduced bighorn sheep population in Badlands National Park, South Dakota we demonstrate the usefulness of neutrality tests and demographic data for detecting a severe genetic bottleneck (Ne < 10). From demographic data the effective population size of the founding population at Badlands was estimated to be six, and a heterozygosity excess test revealed evidence of a severe population bottleneck. We discuss the criteria for intervention when there is evidence of a severe bottleneck, and propose methods of mitigating the potentially deleterious long-term consequences of such bottlenecks. These issues are presented in the context of bighorn sheep reintroductions, but the issues are also of general importance to restoration efforts involving other large vertebrates.

Bighorn sheep were historically a more ubiquitous species in the U.S. west. This report details the 7-year restoration of bighorn sheep to all currently suitable habitats in the national parks of the Rocky Mountain area. A total area of 38,781 sq km was assessed in the 15 NPS units in 6 states and 73 potential restoration sites were identified. Bighorn sheep occupy 22% of this area and restoration was recommended into 7,067 sq km of unoccupied but suitable habitat. Key research findings are also presented.

Elimination of large predators and reduced hunter harvest have led to concerns that an increasing ell (Cervus elaphus) population may be adversely affecting vegetation on the low-elevation elk winter range of Rock Mountain National Park, Colorado, USA. Beaver (Castor canadensis) and their impoundments also have declined dramatically (94%) in the same area over the past 50 years coincident with a 20% decline in willow (Salix spp.) cover. From 1994 to 1998, we studied vegetation production responses of willow communities to elk herbivory and water availability. We estimated willow production by measuring current annual growth of shrubs in 9.3-m 2 circu lar plots, and we measured herbaceous production by clipping vegetation within 0.25-m 2 circular plots. Elk her bivory suppressed willow heights, leader lengths, annual production, and herbaceous productivity of willow corn munities. Water impoundment had a positive effect on herbaceous plant production, but little effect on shrubs, possibly because water tables were naturally high on the study sites even without beaver dams. Nevertheless, the winter range environment previously included more riparian willow habitat because of more stream area (47-69%) due to larger beaver populations. Elk herbivory appears to be the dominant force determining vegetation pro ductivity in willow sites, but the effects may he exacerbated by lowered water tables. Fewer elk or protection from browsing, and water enhancement for

We studied population subdivision and density-dependent and independent factors influencing population processes between 1965 and 2001 for elk (Cervus elaphus) inhabiting Rocky Mountain National Park (park) and the adjacent Estes Valley (town), Colorado, USA. Elk numbers within the park were held relatively constant by management controls until 1967, after which time they were allowed to increase without human interference. Radiotelemetry of 73 elk indicated limited exchange between the subpopulations; combined with clear distinctions in population dynamics, this suggests that these subpopulations are relatively independent despite the absence of physical barriers between them. The elk subpopulation within the park initially increased at 6.5%/year between 1968 and 1970, then growth gradually slowed-exhibiting density-dependent reductions both in calf survival and recruitment with increasing population size-and approached an estimated carrying capacity of 1,069 ± 55 (?±SE). Since 1991, this subpopulation has remained within ±5% of this equilibrium. The adjacent Estes Valley subpopulation grew at an estimated maximum 5-year average rate of 11.0% from 1979 to 1983 and is still increasing at 5.2%/year (1991-2001 average). Estimated town population currently is about 70% of our projected carrying capacity of 2,869 ±415 elk based on projection of observed calf recruitment decline with increasing population. Both carrying-capacity estimates are consistent with independent estimates based on forage biomass and energy considerations. Adult cow survival rate was not found to differ between park and town, and we estimated a constant rate of 0.913 [95% CI = 0.911, 0.915]. Bull survival rates increased in the park from 0.52 to 0.79 between 1965 and 2001, but remained constant at 0.42 [0.35, 0.47] in the Estes Valley. Colder winter temperatures were correlated with reduced calf recruitment (calves:cow at age 0.5 yr) and with reduced calf survival (between age 0.5 and 1.5 yr) in town. Recruitment of town elk also increased with warmer summer temperatures and greater summer precipitation. No weather covariates were significantly correlated with calf recruitment or survival in the park. Declining calf recruitment has been nearly linear and similar in both the park and town. In the park, calf survival responded little to density when the population was well below carrying capacity, but responded at an increasing rate as the population neared carrying capacity. This pattern may explain why calf survival response to density has not yet been detected in town. We estimated current combined population size of 3,049 [2759, 3369] elk in 2001. Elk in the town sector currently outnumber elk in the adjacent national park by almost 2:1 and are projected to increase by 46% before being nutritionally limited, suggesting that human-elk conflicts likely will increase in the absence of active management intervention.

Human recreation has been implicated in the decline of several populations of desert bighorn sheep (Ovis is canadensis nelsoni). Managers are concerned about the impact of increased recreation on desert bighorn sheep in Canyonlands National Park (NP), Utah, USA, where visitation increased 325% from 1979 to 1994. We compared behavioral responses of sheep to recreational activity between a low visitor use area and a high visitor use area during 1993 and 1994 by observing behavioral responses, distances moved, and duration of responses to vehicles, mountain bikers, and humans on foot. Hikers caused the most severe responses in desert bighorn sheep (animals fled in 61% of encounters), followed by vehicles (17% fled) and mountain bikers (6% fled), apparently because hikers were more likely to be in unpredictable locations and often directly approached sheep. We observed considerable individual heterogeneity in responses of bighorn sheep to the greater human use: some animals lived close to the road corridor and were apparently habituated to the human activities, but other animals avoided the road corridor. In the high-use area, we observed 3 radiocollared sheep that lived closer to the road than expected and found evidence of fewer responses to vehicles by females in spring, less response time of all sheep to vehicles in spring, and fewer responses to mountain bikers compared to the low-use area. Overall, there was an avoidance of the road corridor by most other bighorn sheep in the high-use area where all animals, on average, were found 39% farther from roads (490 ± 19 m vs. 354 ± 36 m) than in the low-use area. This avoidance of the road corridor by some animals represented 15% less use of potential suitable habitat in the high-use area over the low-use area. Increased sensitivity to hikers in the high-use area was suggested by a greater responsiveness by males in autumn and greater distance fled by females in spring. Responses of bighorn sheep were greater when human activity approached at the same elevation, when sheep were moving or standing, when female interactions occurred in spring and summer and male interactions occurred in autumn, and when sheep were farther from escape terrain. We recommend managers confine hikers to designated trails during spring lambing and the autumn rut in desert bighorn sheep habitat.

We studied survival of radiocollared elk (Cervus elaphus) calves in Yellowstone National Park from 1987 to 1990, and survival of calves computed from population estimates from 1968 to 1992. We hypothesized that summer and winter survival of elk calves and mass of neonates were inversely related to population size, measures of environmental severity, and timing of births. Herd-wide survival estimates based on winter counts, reported harvests, and herd classifications, suggested that winter survival of elk calves was related inversely to estimated size of the elk population during winter (P = 0.0002), but we found no correlation with an index of winter severity (P = 0.51). Summer survival of elk calves also was correlated inversely with the estimated size of the elk population the previous winter (P = 0.03). Summer survival of radiocollared calves averaged 0.65 (n = 127 marked calves) from 1987 to 1990, the losses mostly due to predation (22%). Winter survival of calves averaged 0.72 (n = 88 marked calves entered the winter period), with losses due mostly to malnutrition (58%). Summer survival of radiocollared calves was positively correlated with estimated birth weight (P = 0.001). Survival of radiocollared calves during winters 1987-90 was correlated positively with early calving and mildness of the winter (in contrast to herd-wide survival estimates), and was inversely correlated with estimated elk population size that winter (P = 0.006). Winter survival of radiocollared calves was lower during 1988-89 following the drought and large fires than the other 3 winters (P < 0.001). Predation on elk calves during summer doubled after the drought and fires of 1988 (13% calf losses to predation before the fires vs. 29% after the fires). Potential compensation existed between components of calf mortality: predators killed more light (P = 0.041) and more late born calves (P = 0.146); calves were born later and lighter (P = 0.048) following severe weather conditions; and heavier born calves survived at a higher rate (P = 0.006). Our results are consistent with the hypothesis that density-dependent mortality of calves during winter due to malnutrition, and summer mortality of calves due to predation were partially compensatory but severe environmental conditions produced largely additive components to both summer (increased predation) and winter (increased malnutrition) mortality.

Calf mortality is a major component of caribou (Rangifer tarandus) population dynamics, but little is known about the timing or causes of calf losses, or of characteristics that predispose calves to mortality. During 1984-87, we radiocollared 226 calves (≤3 days old) in the Denali Caribou Herd (DCH), an unhunted population utilized by a natural complement of predators, to determine the extent, timing, and causes of calf mortality and to evaluate influences of year, sex, birthdate, and birth mass on those losses. Overall, 39% of radio-collared calves died as neonates (≤ 15 days old), and 98% of those deaths were attributed to predation. Most neonatal deaths (85%) occurred within 8 days of birth. Few deaths occurred after the neonatal period (5, 10, and 0% of calves instrumented died during 16-30, 31-150, and >150 days of age, respectively). Survival of neonates was lower (P = 0.038) in 1985, following a severe winter, than during the other 3 years. In years other than 1985, calves born during the peak of calving (approx 50% of the total, born 5-8 days after calving onset) experienced higher (P 10 days old. Wolf predation was not related (P > 0.05) to calf age and peaked 10 days after onset of calving. Grizzly bear and wolf predation on neonates during the calving season was a limiting factor for the Denali Caribou Herd.

Effects of unmanaged populations of large mammalian herbivores, especially elk (Cervus elaphus on vegetation is a concern in Yellowstone National Park, since wolves (Canis Lupus) are extirpated, ungulate migrations are altered by human activities and the disruption of natural process is possible. Stands of low, hedged (height-suppressed) willows (Salix spp.) are observed throughout the greater Yellowstone National Park area where high densities of wintering elk or moose (Alces alces) exist. The height of 47% of the willow stands surveyed on Yellowstone's northern winter range has been suppressed. Mean leader use of willows of all heights was (P < 0.05 in the winter of 1987-88, increased to 60% in winter 1988-89, following the drought and fires of 1988, then declined to 44% in 1989-90 and winter 1990-96. Height-suppressed willows (43 +/- 2 cm, mean +/- SE) were about one-half as tall as tall willows (83 +/- 4 cm). Percent twig use of suppressed willows in summer (25%) and winter (59%) was significantly more than for intermediate or tall stands (P < 0.05). Suppressed willows produced about one-fourth the aboveground annual biomass compared to taller willows; even after 27 or 31 years of protection, previously-suppressed willows produced only one-third the aboveground biomass of taller willows, suggesting suppressed willows grow on sites with lower growth potential. Growth conditions for willows on the northern winter range may have declined due to a warmer and drier climate this century, locally reduced water tables--because of the decline on beaver (Castor canadenis), or fire suppression may be responsible for the observed changes. Tall and intermediate-height willows contained higher concentrations of nitrogen and they exhibited more water stress than height-suppressed willows of the same species. More xeric growth conditions this century than last century, especially during the decades of the 1920's, 1930's, and 1980's, may explain the low growth rates and lower chemical defenses against ungulate herbivory for height-suppressed willows. We propose a more xeric climate and locally-reduced water tables likely contributed to the willow declines on the northern winter range, but that the proximate factor in the declines was herbivory by native ungulates.

Because nutrition is critically related to other aspects of bison (Bison bison) ecology, and the winter ranges inhabited by bison in Yellowstone National Park (YNP) are ecologically diverse, it was important to determine if nutritional deprivation differences occurred among winter ranges. We used chemistry profiles of urine suspended in snow to compare nutritional deprivation of bison from january to April 1988 on 4 sampling areas of 3 winter ranges in YNP. Declining (P < 0.001) trends of urinary potassium: creatinine ratios in bison on all 4 sampling areas indicated progressive nutritional deprivation through late March. Concurrent increases (P ≤ 0.001) in mean urea nitrogen: creatinine ratios from late February through late March in 3 of 4 areas suggested that increased net catabolism was occurring

During 13 January-29 March 1988, we assessed the extent of nutritional deprivation in cow elk (Cervus elaphus nelsoni) groups on the lower, middle, and upper Northern Range and on the Madison-Firehole Range in Yellowstone National Park by 4 sequential collections and chemical analyses of urine excreted in snow (snow-urine). Associated changes in elk density and calf : cow ratios also were estimated during early and late winter or spring. Decreasing (P=0.0001) potassium : creatinine (K:C) ratios throughout winter and increased (P=0.0001) urea nitrogen : creatinine (U:C) on all 4 areas indicated progressive nutritional deprivation and increasing net catabolism of lean body tissue, respectively. These ratios also varied among the 4 sampling areas during early (P=0.0001) and late winter (P

Populations of introduced European wild boar, feral pigs, and combinations of both types (all Susscrola L.) inhabit thirteen areas in the National Park Service system. All parks have relatively stable populations, with the exception of Great Smoky Mountains National Park, which reported a rapidly expanding wild boar population. Suspected and documented impacts were apparently related to pig densities and sensitivity of the ecosystem; the three largest units with dense wild pig populations reported the most damage. Overall, wild pigs are a relatively minor problem for the Park Service; however, problems are severe in at least three parks, and there is potential for invasion of wild boars into several additional parks in the Appalachian Mountains. More specific information is needed on numbers of wild pigs and their impacts in the various parks.

ellowstone National Park is renowned for its fauna of diverse and numerous large mammals. There are hundreds of black and grizzly bears (Ursus americanus and Ursus arctos) that roam the area, and coyotes (Canis latrans) and mountain lions (Felis concolor) as well, but ungulates far outnumber them. Approximately 2500 bison (Bison bison) inhabit the park in three herds (Meagher 1973, 1988). There are also approximately 2500 mule deer (Odocoileus hemionus), 400-500 pronghorn antelope (Antilocapra americana), 250-400 bighorn sheep (Ovis canadensis), and 200 moose (Alces alces) on Yellowstone's northern winter range. In winter, four herds of elk (Cervus elaphus), approximately 22,500 individuals in 1988, inhabit the park and adjacent areas that are part of the northern winter range (Figure 1). Elk from five other herds migrate into the park each summer, increasing the population to approximately 31,000.1 This article focuses on elk, because they are overwhelmingly the dominant park ungulate both in number and total mass. In early 1988 on the northern winter range, there were Fires directly killed few elk, but the fires and drought increased the next winter's die-off

A study was conducted in 1975 on mountain goats (Oreamnos americanus) crossing a highway to visit a natural mineral lick. Eighty-seven successful crossings of the highway involving 692 mountain goats were observed, and an estimated 812 crossings occurred during the 1975 lick season. Crossing success was associated (P

Action des porcs sauvages sur la faune superficielle, les elements nutritifs, la biomasse de la litiere forestiere et du sol