Yellowstone National Park

A trophic cascade recently has been reported among wolves, elk, and aspen on the northern winter range of Yellowstone National Park, Wyoming, USA, but the mechanisms of indirect interactions within this food chain have yet to be established. We investigated whether the observed trophic cascade might have a behavioral basis by exploring environmental factors influencing the movements of 13 female elk equipped with GPS radio collars. We developed a simple statistical approach that can unveil the concurrent influence of several environmental features on animal movements. Paths of elk traveling on their winter range were broken down into steps, which correspond to the straight-line segment between successive locations at 5-hour intervals. Each observed step was paired with 200 random steps having the same starting point, but differing in length and/or direction. Comparisons between the characteristics of observed and random steps using conditional logistic regression were used to model environmental features influencing movement patterns. We found that elk movements were influenced by multiple factors, such as the distance from roads, the presence of a steep slope along the step, and the cover type in which they ended. The influence of cover type on elk movements depended on the spatial distribution of wolves across the northern winter range of the park. In low wolf-use areas, the relative preference for end point locations of steps followed: aspen stands > open areas > conifer forests. As the risks of wolf encounter increased, the preference of elk for aspen stands gradually decreased, and selection became strongest for steps ending in conifer forests in high wolf-use areas. Our study clarifies the behavioral mechanisms involved in the trophic cascade of Yellowstone's wolf-elk-aspen system: elk respond to wolves on their winter range by a shift in habitat selection, which leads to local reductions in the use of aspen by elk.

Morphological diversity within closely related species is an essential aspect of evolution and adaptation. Mutations in the Melanocortin 1 receptor (Mc1r) gene contribute to pigmentary diversity in natural populations of fish, birds, and many mammals. However, melanism in the gray wolf, Canis lupus, is caused by a different melanocortin pathway component, the K locus, that encodes a beta-defensin protein that acts as an alternative ligand for Mc1r. We show that the melanistic K locus mutation in North American wolves derives from past hybridization with domestic dogs, has risen to high frequency in forested habitats, and exhibits a molecular signature of positive selection. The same mutation also causes melanism in the coyote, Canis latrans, and in Italian gray wolves, and hence our results demonstrate how traits selected in domesticated species can influence the morphological diversity of their wild relatives.

Summary The reintroduction of grey wolves Canis lupus (L.) to Yellowstone National Park provides a natural experiment in which to study the effects of a keystone predator on ecosystem function. Grey wolves often provision scavengers with carrion by partially consuming their prey. In order to examine how grey wolf foraging behaviour influences the availability of carrion to scavengers, we observed consumption of 57 wolf‐killed elk Cervus elaphus (L.) and determined the percentage of edible biomass eaten by wolves from each carcass. We found that the percentage of a carcass consumed by wolves increases as snow depth decreases and the ratio of wolf pack size to prey size and distance to the road increases. In addition, wolf packs of intermediate size provide the most carrion to scavengers. Applying linear regression models to the years prior to reintroduction, we calculate carrion biomass availability had wolves been present, and contrast this to a previously published index of carrion availability. Our results demonstrate that wolves increase the time period over which carrion is available, and change the variability in scavenge from a late winter pulse dependent primarily on abiotic environmental conditions to one that is relatively constant across the winter and primarily dependent on wolf demographics. Wolves also decrease the year‐to‐year and month‐to‐month variation in carrion availability. By transferring the availability of carrion from the highly productive late winter, to the less productive early winter and from highly productive years to less productive ones, wolves provide a temporal subsidy to scavengers.

Because some native ungulates have lived without top predators for generations, it has been uncertain whether runaway predation would occur when predators are newly restored to these systems. We show that landscape features and vegetation, which influence predator detection and capture of prey, shape large-scale patterns of predation in a newly restored predator-prey system. We analysed the spatial distribution of wolf (Canis lupus) predation on elk (Cervus elaphus) on the Northern Range of Yellowstone National Park over 10 consecutive winters. The influence of wolf distribution on kill sites diminished over the course of this study, a result that was likely caused by territorial constraints on wolf distribution. In contrast, landscape factors strongly influenced kill sites, creating distinct hunting grounds and prey refugia. Elk in this newly restored predator-prey system should be able to mediate their risk of predation by movement and habitat selection across a heterogeneous risk landscape.

Determining population sizes can be difficult, but is essential for conservation. By counting distinct microsatellite genotypes, DNA from noninvasive samples (hair, faeces) allows estimation of population size. Problems arise because genotypes from noninvasive samples are error-prone, but genotyping errors can be reduced by multiple polymerase chain reaction (PCR). For faecal genotypes from wolves in Yellowstone National Park, error rates varied substantially among samples, often above the 'worst-case threshold' suggested by simulation. Consequently, a substantial proportion of multilocus genotypes held one or more errors, despite multiple PCR. These genotyping errors created several genotypes per individual and caused overestimation (up to 5.5-fold) of population size. We propose a 'matching approach' to eliminate this overestimation bias.

Abstract A “landscape of fear” (LOF) is a map that describes continuous spatial variation in an animal's perception of predation risk. The relief on this map reflects, for example, places that an animal avoids to minimize risk. Although the LOF concept is a potentially unifying theme in ecology that is often invoked to explain the ecological and conservation significance of fear, little is known about the daily dynamics of an LOF. Despite theory and data to the contrary, investigators often assume, implicitly or explicitly, that an LOF is a static consequence of a predator's mere presence within an ecosystem. We tested the prediction that an LOF in a large‐scale, free‐living system is a highly dynamic map with “peaks” and “valleys” that alternate across the diel (24‐h) cycle in response to daily lulls in predator activity. We did so with extensive data from the case study of Yellowstone elk ( Cervus elaphus ) and wolves ( Canis lupus ) that was the original basis for the LOF concept. We quantified the elk LOF, defined here as spatial allocation of time away from risky places and times, across nearly 1,000‐km 2 of northern Yellowstone National Park and found that it fluctuated with the crepuscular activity pattern of wolves, enabling elk to use risky places during wolf downtimes. This may help explain evidence that wolf predation risk has no effect on elk stress levels, body condition, pregnancy, or herbivory. The ability of free‐living animals to adaptively allocate habitat use across periods of high and low predator activity within the diel cycle is an underappreciated aspect of animal behavior that helps explain why strong antipredator responses may trigger weak ecological effects, and why an LOF may have less conceptual and practical importance than direct killing.

Abstract The Greater Yellowstone Ecosystem in the northern Rocky Mountains provides the context for a natural experiment to investigate the response of consumers to resources with differing spatial and temporal dispersion regimes. Grey wolves ( Canis lupus ) and human hunters both provide resource subsidies to scavengers by provisioning them with the remains of their kills. Carrion from hunter kills is highly aggregated in time and space whereas carrion from wolf kills is more dispersed in both time and space. We estimated the total amount of carrion consumed by each scavenger species at both wolf and hunter kills over 4 years. Species with large feeding radii [bald eagles ( Haliaeetus leucocephalus ) and ravens ( Corvus corax )], defined as the area over which a consumer can efficiently locate and integrate resources, dominated consumption at the highly aggregated hunter kills whereas competitively dominant species [coyotes ( Canis latrans )] dominated at the more dispersed wolf kills. In addition, species diversity and the evenness of carrion consumption between scavengers was greater at wolf kills than at hunter kills while the total number of scavengers at hunter kills exceeded those at wolf kills. From a community perspective, the top–down effect of predation is likely to be stronger in the vicinity of highly aggregated resource pulses as species with large feeding radii switch to feeding on alternative prey once the resource pulse subsides.

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 habitats in winter after wolf reintroduction, but did not change their selection of snow water equivalents (SWE) or slope. Elk appear to select habitats that allow them to avoid wolves during summer, but they may rely on other behavioral antipredator strategies, such as grouping, in winter. This study provides evidence that wolves can alter seasonal elk distribution and habitat selection, and demonstrates how the return of wolves to Yellowstone restores important ecosystem processes.

The recovery of the grey wolf in Yellowstone National Park is an outstanding example of a successful reintroduction. A general question concerning reintroduction is the degree to which genetic variation has been preserved and the specific behavioural mechanisms that enhance the preservation of genetic diversity and reduce inbreeding. We have analysed 200 Yellowstone wolves, including all 31 founders, for variation in 26 microsatellite loci over the 10-year reintroduction period (1995-2004). The population maintained high levels of variation (1995 H(0) = 0.69; 2004 H(0) = 0.73) with low levels of inbreeding (1995 F(IS) = -0.063; 2004 F(IS) = -0.051) and throughout, the population expanded rapidly (N(1995) = 21; N(2004) = 169). Pedigree-based effective population size ratios did not vary appreciably over the duration of population expansion (1995 N(e)/N(g) = 0.29; 2000 N(e)/N(g) = 0.26; 2004 N(e)/N(g) = 0.33). We estimated kinship and found only two of 30 natural breeding pairs showed evidence of being related (average r = -0.026, SE = 0.03). We reconstructed the genealogy of 200 wolves based on genetic and field data and discovered that they avoid inbreeding through a wide variety of behavioural mechanisms including absolute avoidance of breeding with related pack members, male-biased dispersal to packs where they breed with nonrelatives, and female-biased subordinate breeding. We documented a greater diversity of such population assembly patterns in Yellowstone than previously observed in any other natural wolf population. Inbreeding avoidance is nearly absolute despite the high probability of within-pack inbreeding opportunities and extensive interpack kinship ties between adjacent packs. Simulations showed that the Yellowstone population has levels of genetic variation similar to that of a population managed for high variation and low inbreeding, and greater than that expected for random breeding within packs or across the entire breeding pool. Although short-term losses in variation seem minimal, future projections of the population at carrying capacity suggest significant inbreeding depression will occur without connectivity and migratory exchange with other populations.

To provide guidance to clinicians about best preventive and therapeutic practices, the Wilderness Medical Society (WMS) convened an expert panel to develop evidence-based guidelines for prevention and treatment of acute mountain sickness, high altitude cerebral edema, and high altitude pulmonary edema. Recommendations are graded based on the quality of supporting evidence and the balance between the benefits and risks/burdens according to criteria put forth by the American College of Chest Physicians. The guidelines also provide suggested approaches to prevention and management of each form of acute altitude illness that incorporate these recommendations. This is an updated version of the original WMS Consensus Guidelines for the Prevention and Treatment of Acute Altitude Illness published in 2010 and subsequently updated as the WMS Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness in 2014.

In the period following wolf ( Canis lupus ) reintroduction to Yellowstone National Park (1995–2004), the northern Yellowstone elk ( Cervus elaphus ) herd declined from ∼17 000 to ∼8000 elk (8.1% yr −1 ). The extent to which wolf predation contributed to this decline is not obvious because the influence of other factors (human harvest and lower than average annual rainfall) on elk dynamics has not been quantified. To assess the contribution of wolf predation to this elk decline, we built and assessed models based on elk‐related data prior to wolf reintroduction (1961 to 1995). We then used the best of these models to predict how elk dynamics might have been realized after wolf reintroduction (1995 to 2004) had wolves never been reintroduced. The best performing model predicted 64% of the variance in growth rate and included elk abundance, harvest rate, annual snowfall, and annual precipitation as predictor variables. The best performing models also suggest that harvest may be super‐additive. That is, for every one percent increase in harvest rate, elk population growth rate declines by more than one percent. Harvest rate also accounted for ∼47% of the observed variation in elk growth rate. According to the best‐performing model, which accounts for harvest rate and climate, the elk population would have been expected to decline by 7.9% per year, on average, between 1995 and 2004. Within the limits of uncertainty, which are not trivial, climate and harvest rate are justified explanations for most of the observed elk decline. To the extent that this is true, we suggest that between 1995 and 2004 wolf predation was primarily compensatory.

ABSTRACT We conducted a 3-year study (May 2003–Apr 2006) of mortality of northern Yellowstone elk (Cervus elaphus) calves to determine the cause for the recruitment decline (i.e., 33 calves to 13 calves/100 adult F) following the restoration of wolves (Canis lupus). We captured, fit with radiotransmitters, and evaluated blood characteristics and disease antibody seroprevalence in 151 calves ≤6 days old (68M:83F). Concentrations (x̄, SE) of potential condition indicators were as follows: thyroxine (T4; 13.8 μg/dL, 0.43), serum urea nitrogen (SUN; 17.4 mg/dL, 0.57), γ-glutamyltransferase (GGT; 66.4 IU/L, 4.36), gamma globulins (GG; 1.5 g/dL, 0.07), and insulin-like growth factor-1 (IGF-1; 253.6 ng/mL, 9.59). Seroprevalences were as follows: brucellosis (Brucella abortus; 3%), bovine-respiratory syncytial virus (3%), bovine-viral-diarrhea virus type 1 (25%), infectious-bovine rhinotracheitis (58%), and bovine parainfluenza-3 (32%). Serum urea nitrogen, GGT, GG, and IGF-1 varied with year; T4, SUN, and GG varied with age (P ≤ 0.01); and SUN varied by capture area (P = 0.02). Annual survival was 0.22 (SE = 0.035, n = 149) and varied by calving area but not year. Neonates captured in the Stephens Creek/Mammoth area of Yellowstone National Park, USA, had annual survival rates >3× higher (0.54) than those captured in the Lamar Valley area (0.17), likely due to the higher predator density in Lamar Valley. Summer survival (20 weeks after radiotagging) was 0.29 (SE = 0.05, n = 116), and calving area, absolute deviation from median birth date, and GG were important predictors of summer survival. Survival during winter (Nov-Apr) was 0.90 (SE= 0.05, n = 42), and it did not vary by calving area or year. Sixty-nine percent (n = 104) of calves died within the first year of life, 24% (n = 36) survived their first year, and 7% (n = 11) had unknown fates. Grizzly bears (Ursus arctos) and black bears (Ursus americanus) accounted for 58–60% (n = 60–62) of deaths, and wolves accounted for 14–17% (n = 15–18). Summer predation (95% of summer deaths) increased, and winter malnutrition (0% of winter deaths) decreased, compared with a similar study during 1987–1990 (72% and 58%, respectively). Physiological factors (e.g., low levels of GG) may predispose calves to predation. Also, the increase in bear numbers since wolf restoration and spatial components finer than the northern range should be considered when trying to determine the causes of the northern Yellowstone elk decline. This is the first study to document the predation impacts from reintroduced wolves on elk calf mortality in an ecosystem already containing established populations of 4 other major predators (i.e., grizzly and black bears, cougars [Puma concolor], and coyotes [Canis latrans]). The results are relevant to resource managers of the Yellowstone ecosystem in understanding the dynamics of the elk population, in providing harvest quota recommendations for local elk hunts to the Montana Department of Fish, Wildlife and Parks, the United States Fish and Wildlife Service regarding wolf and grizzly bear recovery, and to all areas worldwide where predators are increasing, by providing managers with information about potential carnivore impacts on elk populations. RESEMEN Hemos realizado un estudio de 3 años (may 2003–abr 2006) sobre la mortalidad de las crías de wapiti (Cervus elaphus) en el norte de Yellowstone para determinar las causas del descenso del reclutamiento (de 33 a 13 crías /100 hembras adultas) tras la restauración del lobo (Canis lupus). Hemos capturado, marcado con radiotransmisores y evaluado las características de la sangre y la seroprevalencia de los anticuerpos a enfermedades de 151 crías ≤6 días (68M:83H). Las concentraciones (x̄, SE) de los indicadores del estado potencial de salud fueron: tiroxina (T4; 13.8 μg/dL, 0.43), nitrógeno de urea en suero (SUN; 17.4 mg/dL, 0.57), γ-glutamiltransferasa (GGT; 66.4 IU/L, 4.36), gamma globulinas (GG; 1.5 g/dL, 0.07) y factor de crecimiento insulinoide tipo 1 (IGF-1; 253.6 ng/mL, 9.59). Las seroprevalencias fueron: brucelosis (Brucella abortus; 3%), virus respiratorio sincitial bovino (3%), virus de la diarrea viral bovina tipo 1 (25%), rinotraqueítis infecciosa bovina (58%) y parainfluenza bovina tipo 3 (32%). El SUN, la GGT, las GG y el IGF-1 variaron con el año; la T4, el SUN y las GG variaron con la edad (P ≤ 0.01); y el SUN varió con el area decaptura (P = 0.02). La supervivencia anual fue del 0.22 (SE=0.035, n = 149) y varió con la zona de reproducción pero no con el año. Los neonatos capturados en la zona de Stephens Creek/Mammoth del Parque Nacional de Yellowstone, EE.UU., tuvieron tasas de supervivencia anual más de 3 veces superiores (0.54) a las de los capturados en la zona del valle de Lamar (0.17), presumiblemente por la mayor densidad de predadores en el valle de Lamar. La supervivencia estival (20 semanas después del radiomarcaje) fue 0.29 (SE = 0.05, n = 116); la zona de partos, la desviación absoluta de la mediana de la fecha de nacimiento y las GG fueron predictores importantes de la supervivencia estival. La supervivencia durante el invierno (nov-abr) fue 0.90 (SE= 0.05, n = 42) y no varió con la zona de partos o con el año. El 69% (n = 104) de las crías murieron antes de cumplir un año, el 24% (n = 36) sobrevivieron más de un año y se desconoce el destino del 7% (n = 11). Los osos grizzly (Ursus arctos) y los osos negros (Ursus americanus) fueron responsables del 58–60% (n = 60–62) de las muertes, y los lobos, del 14–17% (n = 15–18). La predación estival (95% de las muertes en verano) aumentó, y la malnutrición en invierno (0% de las muertes en invierno) disminuyó en comparación con un estudio similar realizado durante 1987–1990 (72% y 58%, respectivamente). Los factores fisiológicos (bajos niveles de GG) quizá predisponen a las crías a ser predadas. Además, el aumento de la población de osos desde la restauración del lobo y algunos componentes espaciales más sutiles en las montañas septentrionales deberían ser considerados al tratar de determinar las causas del declive del wapiti en el norte de Yellowstone. Este es el primer estudio que describe el impacto que la predación de lobos reintroducidos tiene sobre la mortalidad de las crías de wapiti en un ecosistema donde ya existen poblaciones establecidas de otros 4 grandes predadores (osos grizzly y negro, pumas [Puma concolor] y coyotes [Canis latrans]). Los resultados son relevantes para los gestores de recursos del ecosistema de Yellowstone porque ayudan a comprender la dinámica de las poblaciones de wapiti; aportan recomendaciones al Departamento de Pesca, Vida Silvestre y Parques de Montana para decidir cuotas de extracción de wapiti en las cacerías locales, al Servicio de Pesca y Vida Silvestre de los Estados Unidos en relación a la recuperacion del lobo y el oso grizzly; y ofrecen a los gestores información acerca de los impactos potenciales de los carnívoros sobre las poblaciones de wapiti en todas las zonas del mundo donde los predadores están aumentando. RÉSUMÉ Nous avons realise une etude de 3 ans (mai 2003–avr 2006) portant sur les faons des wapitis du nord de Yellowstone afin de déterminer les causes du déclin de recrutement (c.-à-d. de 33 à 13 faons/100 femelles adultes) qui a suivi la réintroduction du loup (Canis lupus). Nous avons capturé, prélevé un échantillon sanguin et muni d'un radioémetteur 151 faons de ≤6 jours (68M:83F). Les concentrations (x̄, ET) d'indicateurs potentiels de condition physique étaient: thyroxine (T4; 13.8 μg/dL, 0.43), azote uréique sérique (AUS; 17.4 mg/dL, 0.57), γ-glutamyltransférase (GGT; 66.4 IU/L, 4.36), gamma globulines (GG; 1.5 g/dL, 0.07) et facteur de croissance insulinomimétique de type 1 (FCI-1; 253.6 ng/mL, 9.59). La prévalence sérique d'anticorps était: brucellose (Brucella abortus; 3%), virus syncitial respiratoire bovin (3%), virus diarrhéique bovin de type 1 (25%), rhinotrachéite infectieuse bovine (58%) et parainfluenza-3 bovin (32%). L'azote uréique sérique, la GGT, les GG et le FCI-1 ont varié entre les années; la T4, l'AUS et les GG varièrent en fonction de l'ǎge (P < 0.01) et l'AUS en fonction du lieu de capture (P = 0.02). Le taux annuel de survie atteignit 0.22 (ET = 0.035, n = 149) et varia en fonction de l'aire de mise bas mais non de l'année. Les faons nés dans l'aire de Stephens Creek/Mammoth du parc national de Yellowstone, États-Unis, possédaient des taux annuels de survie plus de 3 fois supérieurs (0.54) à ceux capturés dans l'aire de Lamar Valley (0.17), vraisemblablement à cause d'une densité de prédateurs plus élevée au second endroit. La survie estivale moyenne (20 semaines suivant le marquage) était de 0.29 (ET = 0.05, n = 116) et elle dépendait fortement du lieu de mise bas, de la déviation absolue de la date de naissance médiane et de la concentration de GG. La survie hivernale (nov-avr) atteignait 0.90 (ET= 0.05, n = 42) et ne variait ni en fonction du lieu de naissance ou de l'année. Soixante-neuf pourcent (n = 104) des faons moururent durant leur premiere année, 24% (n = 36) survécurent et le sort de 7% (n = 11) demeura inconnu. Les ours grizzlys (Ursus arctos) etles ours noirs (Ursus americanus) furent responsables de 58–60% des mortalités (n = 60–62), contre 14–17% pour les loups (n = 15–18). La prédation estivale (95% des mortalités) augmenta et la malnutrition hivernale (0% des mortalités) diminua en comparaison avec une etude similaire réalisée de 1987 à 1990 (72% et 58%, respectivement). Des facteurs physiologiques (c.-à-d. des bas niveaux de GG) pourraient prédisposer les faons à la prédation. Par ailleurs, l'accroissement du nombre d'ours depuis la réintroduction du loup et des composantes spatiales plus fines que celles de notre etude devraient ětre pris en compte en tentant de determiner les causes du déclin du nombre de wapitis du nord de Yellowstone. Notre etude s'avère la première à documenter les impacts de la prédation de loups réintroduits dans un écosystème contenant des populations établies de 4 prédateurs majeurs (c.-à-d., les ours grizzlys et noirs, les cougars [Puma concolor], les coyotes [Canis latrans]). Nos résultats concernent les gestionnaires de l'écosystème de Yellowstone puisqu'ils permettent de comprendre la dynamique de la population de wapitis, qu'ils fournissent des recommandations pour les chasses locales au Montana Department of Fish, Wildlife and Parks et d'autres, pour la gestion du loup et de l'ours grizzly, au U.S. Fish and Wildlife Service. Nos résultats concernent également toutes les regions du monde où les prédateurs s'accroissent puisqu'ils fournissent aux gestionnaires des informations concernant l'impact potentiel des carnivores sur les populations de grands herbivores.

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.

, genes previously implicated in the behavioral phenotype of patients with WBS and contained within the WBS locus, contribute to extreme sociability in dogs. This finding suggests that there are commonalities in the genetic architecture of WBS and canine tameness and that directional selection may have targeted a unique set of linked behavioral genes of large phenotypic effect, allowing for rapid behavioral divergence of dogs and wolves, facilitating coexistence with humans.

Despite the popular view that social predators live in groups because group hunting facilitates prey capture, the apparent tendency for hunting success to peak at small group sizes suggests that the formation of large groups is unrelated to prey capture. Few empirical studies, however, have tested for nonlinear relationships between hunting success and group size, and none have demonstrated why success trails off after peaking. Here, we use a unique dataset of observations of individually known wolves (Canis lupus) hunting elk (Cervus elaphus) in Yellowstone National Park to show that the relationship between success and group size is indeed nonlinear and that individuals withholding effort (free riding) is why success does not increase across large group sizes. Beyond 4 wolves, hunting success leveled off, and individual performance (a measure of effort) decreased for reasons unrelated to interference from inept hunters, individual age, or size. But performance did drop faster among wolves with an incentive to hold back, i.e., nonbreeders with no dependent offspring, those performing dangerous predatory tasks, i.e., grabbing and restraining prey, and those in groups of proficient hunters. These results suggest that decreasing performance was free riding and that was why success leveled off in groups with >4 wolves that had superficially appeared to be cooperating. This is the first direct evidence that nonlinear trends in group hunting success reflect a switch from cooperation to free riding. It also highlights how hunting success per se is unlikely to promote formation and maintenance of large groups.

Wolf (Canis lupus) impacts on prey are a central post-wolf-reintroduction issue in the greater Yellowstone ecosystem (GYE) of the western United States. Further, estimates of wolf kill rates, used to understand these impacts, can be biased due to unrecovered kills. In Yellowstone National Park (YNP), visibility of wolves allowed us to combine independent aerial and ground observations and use a double-count method to estimate the probability of recovering kills. We consequently used these data to adjust estimates of wolf kill rates. We conducted monitoring annually from 1995 to 2000 during 2 30-day periods in early (15 Nov–14 Dec) and late winter (Mar). Estimated recovery rates of wolf kills for ground and aerial crews were 50% and 45%, respectively, although we determined that this varied by location (distance from road) and possibly age (calf or adult) of the kill. The estimated combined recovery rate was 73%. Estimated wolf kill rates were higher in late winter (2.2 kills/wolf/month) compared to early winter (1.6 kills/wolf/month), with an overall estimated rate of 1.9 kills/wolf/month. The primary prey of wolves in winter was elk (Cervus elaphus; 90%). During our study, 43% of the elk killed were calves, 28% were adult females (cows), 21% were adult males (bulls), and 9% were of unknown age/sex. Comparing prey selection to prey availability, wolf packs residing on the northern range (NR) of the GYE selected for calves, against cows, and approximately proportional to availability for bulls. Prey use was different for wolf packs occupying the NR compared to packs residing in other areas (non-northern range [NNR]) and varied seasonally for NR packs. Variation in wolf kill rates by season, and the relative stability of the northern Yellowstone elk herd during a series of mild winters despite increases in wolf density, suggest that kill rates and ultimately elk population size are influenced by winter weather. Management of ungulates should reflect the addition of wolves combined with the unpredictability of winter weather in the mountainous terrain of the western United States.

Explaining and predicting animal movement in heterogeneous landscapes remains challenging. This is in part because movement paths often include a series of short, localized displacements separated by longer‐distance forays. This multiphasic movement behavior reflects the complex response of an animal to present environmental conditions and to its internal behavioral state. This state is an autocorrelated process influenced by preceding behaviors and habitats visited. Movement patterns depending on the behavioral state of an animal represent the broad‐scale response of that animal to the environment. Quantifying how animals respond both to local conditions and to their internal state reveals how animals respond to spatial heterogeneity at different spatial scales. We used a state–space statistical approach to model the internal behavioral state and the proximate movement response of elk ( Cervus elaphus ) to available forage biomass, landscape composition, topography, and wolf ( Canis lupus ) density during summer in Yellowstone National Park, USA. We analyzed movement paths of 16 female elk fitted with global positioning system (GPS) radio collars that recorded locations at 5‐h intervals. Habitat variables were quantified within 175 m radii (one‐half of the median 5‐h displacement) centered on the beginning location of each interval. Stepwise model selection identified models that best explained the movement distances of each animal. The behavioral state changed very slowly for most animals (median autocorrelation r = 0.93), and all animals responded strongly to time of day (with more movement in the crepuscular hours). However, the spatial variables included in the best‐fitting models varied substantially among individual elk. These results suggest that strong patterns of habitat selection observed in other studies may result from frequent visits to preferred areas rather than a reduction of movement in those areas.

A sample of 40 fire—scarred trees was used to reconstruct the frequency and size of fires during the past 300—400 years in northern Yellowstone National Park. Best estimates of frequency suggested mean intervals of about 20—25 years between fires, after adjustments had been made for the recent influence of modern man. Agreement in fire dates over wide areas suggested the occurence of 8 or 10 extensive fires in the past 300—400 years. Euro—American man has substantially reduced the natural fire frequency for about 80 years and has thus contributed to changes in plant succession.

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.

1. For large predators living in seasonal environments, patterns of predation are likely to vary among seasons because of related changes in prey vulnerability. Variation in prey vulnerability underlies the influence of predators on prey populations and the response of predators to seasonal variation in rates of biomass acquisition. Despite its importance, seasonal variation in predation is poorly understood. 2. We assessed seasonal variation in prey composition and kill rate for wolves Canis lupus living on the Northern Range (NR) of Yellowstone National Park. Our assessment was based on data collected over 14 winters (1995-2009) and five spring-summers between 2004 and 2009. 3. The species composition of wolf-killed prey and the age and sex composition of wolf-killed elk Cervus elaphus (the primary prey for NR wolves) varied among seasons. 4. One's understanding of predation depends critically on the metric used to quantify kill rate. For example, kill rate was greatest in summer when quantified as the number of ungulates acquired per wolf per day, and least during summer when kill rate was quantified as the biomass acquired per wolf per day. This finding contradicts previous research that suggests that rates of biomass acquisition for large terrestrial carnivores tend not to vary among seasons. 5. Kill rates were not well correlated among seasons. For example, knowing that early-winter kill rate is higher than average (compared with other early winters) provides little basis for anticipating whether kill rates a few months later during late winter will be higher or lower than average (compared with other late winters). This observation indicates how observing, for example, higher-than-average kill rates throughout any particular season is an unreliable basis for inferring that the year-round average kill rate would be higher than average. 6. Our work shows how a large carnivore living in a seasonal environment displays marked seasonal variation in predation because of changes in prey vulnerability. Patterns of wolf predation were influenced by the nutritional condition of adult elk and the availability of smaller prey (i.e. elk calves, deer). We discuss how these patterns affect our overall understanding of predator and prey population dynamics.