Cougars, wolves, and humans drive a dynamic landscape of fear for elk

To manage predation risk, prey navigate a dynamic landscape of fear, or spatiotemporal variation in risk perception, reflecting predator distributions, traits, and activity cycles. Prey may seek to reduce risk across this landscape using habitat at times and in places when predators are less active. In multipredator landscapes, avoiding one predator could increase vulnerability to another, making the landscape of fear difficult to predict and navigate. Additionally, humans may shape interactions between predators and prey, and induce new sources of risk. Humans can function as a shield, providing a refuge for prey from human-averse carnivores, and as a predator, causing mortality through hunting and vehicle collisions and eliciting a fear response that can exceed that of carnivores. We used telemetry data collected between 2017 and 2021 from 63 Global Positioning System-collared elk (Cervus canadensis), 42 cougars (Puma concolor), and 16 wolves (Canis lupus) to examine how elk habitat selection changed in relation to carnivores and humans in northeastern Washington, USA. Using step selection functions, we evaluated elk habitat use in relation to cougars, wolves, and humans, diel period (daytime vs. nighttime), season (summer calving season vs. fall hunting season), and habitat structure (open vs. closed habitat). The diel cycle was critical to understanding elk movement, allowing elk to reduce encounters with predators where and when they would be the largest threat. Elk strongly avoided cougars at night but had a near-neutral response to cougars during the day, whereas elk avoided wolves at all times of day. Elk generally used more open habitats where cougars and wolves were most active, rather than altering the use of habitat structure depending on the predator species. Elk avoided humans during the day and ~80% of adult female mortality was human caused, suggesting that humans functioned as a "super predator" in this system. Simultaneously, elk leveraged the human shield against wolves but not cougars at night, and no elk were confirmed to have been killed by wolves. Our results add to the mounting evidence that humans profoundly affect predator-prey interactions, highlighting the importance of studying these dynamics in anthropogenic areas.

Experimental SARS-CoV-2 Infection of Elk and Mule Deer

To assess the susceptibility of elk (Cervus canadensis) and mule deer (Odocoileus hemionus) to SARS-CoV-2, we performed experimental infections in both species. Elk did not shed infectious virus but mounted low-level serologic responses. Mule deer shed and transmitted virus and mounted pronounced serologic responses and thus could play a role in SARS-CoV-2 epidemiology.

Associations between hair trace mineral concentrations and the occurrence of treponeme-associated hoof disease in elk (Cervus canadensis)

BACKGROUND

Trace minerals are important for animal health. Mineral deficiency or excess can negatively affect immune function, wound healing, and hoof health in domestic livestock, but normal concentrations and health impairment associated with mineral imbalances in wild animals are poorly understood. Treponeme-associated hoof disease (TAHD) is an emerging disease of free-ranging elk (Cervus canadensis) in the U.S. Pacific Northwest. Selenium and copper levels identified in a small number of elk from areas where TAHD is established (i.e., southwestern Washington) suggested a mineral deficiency may have increased susceptibility to TAHD. Our objectives were to determine trace mineral concentrations using hair from elk originating in TAHD affected areas of Washington, California, Idaho, and Oregon and assess their associations with the occurrence of the disease.

RESULTS

We identified limited associations between TAHD occurrence and severity with hair mineral concentrations in 72 free-ranging elk, using Firth's logistic regression and multinomial regression models. We found consistent support for a priori hypotheses that selenium concentration, an important mineral for hoof health, is inversely associated with the occurrence of TAHD. Less consistent support was observed for effects of other minerals previously associated with hoof health (e.g., copper or zinc) or increased disease risk from potential toxicants.

CONCLUSION

Trace mineral analysis of hair is a non-invasive sampling technique that offers feasibility in storage and collection from live animals and carcasses. For some minerals, levels in hair correlate with visceral organs that are challenging to obtain. Our study using hair collected opportunistically from elk feet submitted for diagnostic investigations provides a modest reference of hair mineral levels in elk from the U.S. Pacific Northwest that may be useful in future determination of reference ranges. Although our results revealed high variability in mineral concentrations between elk, consistent relationship of possibly low selenium levels and TAHD suggest that further investigations are warranted.

Wolf spatial behavior promotes encounters and kills of abundant prey

Predators use different spatial tactics to track the prey on the landscape. Three hypotheses describe spatial tactics: prey abundance for prey that are aggregated in space; prey habitat for uniformly distributed prey; and prey catchability for prey that are difficult to catch and kill. The gray wolf (Canis lupus) is a generalist predator that likely employs more than one spatial hunting tactic to match their diverse prey with distinct distributions and behavior that are available. We conducted a study on 17 GPS collared wolves in 6 packs in Riding Mountain National Park, Manitoba, Canada where wolves prey on moose (Alces alces) and elk (Cervus canadensis). We evaluated wolf selection for prey density, habitat selection and catchability on the landscape through within-territory habitat selection analysis. We reveal support for both the prey habitat and prey catchability hypotheses. For moose, their primary prey, wolves employed a mixed habitat and catchability tactic. Wolves used spaces described by the intersection of moose habitat and moose catchability. Wolves selected for the catchability of elk, their secondary prey, but not elk habitat. Counter to our predictions, wolves avoided areas of moose and elk density, likely highlighting the ongoing space race between predator and prey. We illustrate that of the three hypotheses the primary driver was prey catchability, where the interplay of both prey habitat with catchability culminate in predator spatial behaviour in a multiprey system.

Evaluating the summer landscapes of predation risk and forage quality for elk (Cervus canadensis)

The recovery of carnivore populations in North American has consequences for trophic interactions and population dynamics of prey. In addition to direct effects on prey populations through killing, predators can influence prey behavior by imposing the risk of predation. The mechanisms through which patterns of space use by predators are linked to behavioral response by prey and nonconsumptive effects on prey population dynamics are poorly understood. Our goal was to characterize population‐ and individual‐level patterns of resource selection by elk (Cervus canadensis) in response to risk of wolves (Canis lupus) and mountain lions (Puma concolor) and evaluate potential nonconsumptive effects of these behavioral patterns. We tested the hypothesis that individual elk risk‐avoidance behavior during summer would result in exposure to lower‐quality forage and reduced body fat and pregnancy rates. First, we evaluated individuals' second‐order and third‐order resource selection with a used‐available sampling design. At the population level, we found evidence for a positive relationship between second‐ and third‐order selection and forage, and an interaction between forage quality and mountain lion risk such that the relative probability of use at low mountain lion risk increased with forage quality but decreased at high risk at both orders of selection. We found no evidence of a population‐level trade‐off between forage quality and wolf risk. However, we found substantial among‐individual heterogeneity in resource selection patterns such that population‐level patterns were potentially misleading. We found no evidence that the diversity of individual resource selection patterns varied predictably with available resources, or that patterns of individual risk‐related resource selection translated into biologically meaningful changes in body fat or pregnancy rates. Our work highlights the importance of evaluating individual responses to predation risk and predator hunting technique when assessing responses to predators and suggests nonconsumptive effects are not operating at a population scale in this system.

Large herbivores in a partially migratory population search for the ideal free home

Migration is a tactic used across taxa to access resources in temporally heterogenous landscapes. Populations that migrate can attain higher abundances because such movements allow access to higher quality resources, or reduction in predation risk resulting in increased fitness. However, most migratory species occur in partially migratory populations, a mix of migratory and non-migratory individuals. It is thought that the portion of migrants in a partial migration population is maintained either through 1) a population-level evolutionary stable state where counteracting density-dependent vital rates act on migrants and residents to balance fitness, or 2) conditional migration, where the propensity to migrate is influenced by the individual's state. However, in many respects, migration is also a form of habitat selection and the proportion of migrants and residents may be the result of density-dependent habitat selection. Here, we test whether the theory of Ideal Free Distribution (IFD) can explain the coexistence of different migratory tactics in a partially migratory population. IFD predicts individuals exhibit density-dependent vital rates and select different migratory tactics to maximize individual fitness resulting in equal fitness (λ) between tactics. We tested the predictions of IFD in a partially migratory elk population that declined by 70% with 19 years of demographic data and migratory tactic switching rates from >300 individuals. We found evidence of density dependence for resident pregnancy and adult female survival providing a fitness incentive to switch tactics. Despite differences in vital rates between migratory tactics, mean λ (fitness) was equal. However, as predicted by the IFD, individuals switched tactics toward those of higher fitness. Our analysis reveals that partial migration may be driven by tactic selection that follows the ideal free distribution. These findings reinforce that migration across taxa may be a polymorphic behavior in large herbivores where migratory tactic selection is determined by differential costs and benefits, mediated by density-dependence.

Individual differences in habitat selection mediate landscape level predictions of a functional response

Predicting future space use by animals requires models that consider both habitat availability and individual differences in habitat selection. The functional response in habitat selection posits animals adjust their habitat selection to availability, but population-level responses to availability may differ from individual responses. Generalized functional response (GFR) models account for functional responses by including fixed effect interactions between habitat availability and selection. Population-level resource selection functions instead account for individual selection responses to availability with random effects. We compared predictive performance of both approaches using a functional response in elk (Cervus canadensis) selection for mixed forest in response to road proximity, and avoidance of roads in response to mixed forest availability. We also investigated how performance changed when individuals responded differently to availability from the rest of the population. Individual variation in road avoidance decreased performance of both models (random effects: β = 0.69, 95% CI 0.47, 0.91; GFR: β = 0.38, 95% CI 0.05, 0.71). Changes in individual road and forest availability affected performance of neither model, suggesting individual responses to availability different from the functional response mediated performance. We also found that overall, both models performed similarly for predicting mixed forest selection (F_{1, 58} = 0.14, p = 0.71) and road avoidance (F_{1, 58} = 0.28, p = 0.60). GFR estimates were slightly better, but its larger number of covariates produced greater variance than the random effects model. Given this bias-variance trade-off, we conclude that neither model performs better for future space use predictions.

DICTYOCAULUS CERVI-LIKE LUNGWORM INFECTION IN A ROCKY MOUNTAIN ELK (CERVUS CANADENSIS NELSONI) FROM WYOMING, USA

Dictyocaulus spp. infections are common in North American cervids, with Dictyocaulus viviparus described as most common. A Rocky Mountain elk (Cervus canadensis nelsoni) was found dead in Wyoming, US with significant bronchitis and pneumonia. In the bronchi and trachea, numerous large nematodes were found and grossly identified as Dictyocaulus spp. lungworms. Macroscopic alterations, such as distended interlobular septa and edema with foam and mucus observed on cut surface and in trachea and bronchi, were consistent with those commonly described in D. viviparus infections. Female lungworms were identified to Dictyocaulus spp. level via morphologic examination and molecular analyses based on mitochondrial cyclooxygenase 1 and 18S ribosomal RNA genes. A phylogenetic analysis was conducted employing the maximum likelihood method. Based on both morphologic and genetic assays, the isolated lungworms were most likely a strain of Dictyocaulus cervi. Within the female adult worms, free first stage larvae were observed besides worm eggs, which had not been described for Dictyocaulus spp. Phylogenetic analysis revealed that our parasites clustered closely with D. cervi, forming a subclade with that species within a larger clade that includes Dictyocaulus eckerti. While the elk tested positive for chronic wasting disease, it is assumed that significant pathology in the present case was caused directly by infection with the D. cervi-like lungworm, not previously described in North America.

Surveillance for Babesia odocoilei in Hunter-Harvested Wild-Elk (Cervus elaphus canadensis) from Pennsylvania, USA (2016-2017)

Babesia odocoilei is a tick-borne protozoal parasite which infects the erythrocytes of members of the families Cervidae and Bovidae. Infection can result in hemolytic anemia, lethargy, anorexia, and death. The reservoir host of B. odocoilei is the white-tailed deer (Odocoileus virginianus); however, infections with overt disease have only been documented in reindeer (Rangider tarandu tarandus), caribou (Rangider tarandu caribou) and captive elk (Cervus elaphus canadensis). Infected elk may remain asymptomatic, creating the risk for dissemination of the pathogen when elk are relocated. Additionally, infected asymptomatic elk may contribute to the spread of B. odocoilei in the local wildlife/captive population via feeding ticks. Information regarding endemic regions of B. odocoilei infection is limited due to frequent asymptomatic infections and a lack of targeted surveillance of B. odocoilei in wildlife. To obtain data on B. odocoilei infection in wild elk in Pennsylvania, we tested blood samples collected from 190 hunter-harvested wild elk between 2016 and 2017. Of the 190 blood samples tested, 18.4% (35/190) tested positive for Babesia spp. Genetic sequencing of the positive samples showed a 98.0–100.0% match for B. odocoilei. No other Babesia species were identified. Results of this study documents B. odocoilei infection within hunter-harvested wild elk from Pennsylvania.

Prevalence of Winter Ticks (Dermacentor albipictus) in Hunter-Harvested Wild Elk (Cervus canadensis) from Pennsylvania, USA (2017-2018)

Winter ticks (Dermacentor albipictus) are an aggressive one-host tick that infest a wide-diversity of ungulates. Infestations can result in anemia, alopecia, emaciation, and death. Most notably, the winter tick has caused negative impacts to moose (Alces alces) populations in the northeast United States and Canada. Winter ticks have been identified on other cervid species, including deer (Odocoileus virginianus) and elk (Cervus canadensis), which generally results in low tick burdens and mild or no disease. Recently, however, a wild yearling bull elk in Pennsylvania was found dead as a result of severe winter tick infestation. To obtain baseline data on winter ticks in wild elk in Pennsylvania, we collected 1453 ticks from 190 hunter-harvested wild elk between 2017-2018. Of the 204 harvested elk, 94.3% (190/204) had ticks collected for this study and none of the sampled elk had evidence of winter-tick associated disease. The average tick burden was 7.7 ticks/elk and average winter tick load on all elk was 0.5. Results of this study indicate that winter ticks do infest wild elk in Pennsylvania. However, during the fall months, the tick burden is low and rarely associated with lesions. These data herein serve as a baseline to monitor winter tick populations over time.

Sex-Specific Elk Resource Selection during the Anthrax Risk Period

Anthrax, caused by the spore-forming bacterium Bacillus anthracis, is a zoonosis affecting animals and humans globally. In the United States, anthrax outbreaks occur in wildlife and livestock, with frequent outbreaks in native and exotic wildlife species in Texas, livestock outbreaks in the Dakotas, and sporadic mixed outbreaks in Montana. Understanding where pathogen and host habitat selection overlap is essential for anthrax management. Resource selection and habitat use of ungulates may be sex-specific and lead to differential anthrax exposure risks across the landscape for males and females. We evaluated female elk (Cervus canadensis) resource selection in the same study areas as male elk in a previous anthrax risk study to identify risk of anthrax transmission to females and compare transmission risk between females and males. We developed a generalized linear mixed-effect model to estimate resource selection for female elk in southwest Montana during the June to August anthrax transmission risk period. We then predicted habitat selection of female and male elk across the study area and compared selection with the distribution of anthrax risk to identify spatial distributions of potential anthrax exposure for the male and female elk. Female and male elk selected different resources during the anthrax risk period, which resulted in different anthrax exposure areas for females and males. The sex-specific resource selection and habitat use could infer different areas of risk for anthrax transmission, which can improve anthrax and wildlife management and have important public health and economic implications.

Wave-like Patterns of Plant Phenology Determine Ungulate Movement Tactics

Animals exhibit a diversity of movement tactics [1]. Tracking resources that change across space and time is predicted to be a fundamental driver of animal movement [2]. For example, some migratory ungulates (i.e., hooved mammals) closely track the progression of highly nutritious plant green-up, a phenomenon called "green-wave surfing" [3-5]. Yet general principles describing how the dynamic nature of resources determine movement tactics are lacking [6]. We tested an emerging theory that predicts surfing and the existence of migratory behavior will be favored in environments where green-up is fleeting and moves sequentially across large landscapes (i.e., wave-like green-up) [7]. Landscapes exhibiting wave-like patterns of green-up facilitated surfing and explained the existence of migratory behavior across 61 populations of four ungulate species on two continents (n = 1,696 individuals). At the species level, foraging benefits were equivalent between tactics, suggesting that each movement tactic is fine-tuned to local patterns of plant phenology. For decades, ecologists have sought to understand how animals move to select habitat, commonly defining habitat as a set of static patches [8, 9]. Our findings indicate that animal movement tactics emerge as a function of the flux of resources across space and time, underscoring the need to redefine habitat to include its dynamic attributes. As global habitats continue to be modified by anthropogenic disturbance and climate change [10], our synthesis provides a generalizable framework to understand how animal movement will be influenced by altered patterns of resource phenology.

Living with liver flukes: Does migration matter?

Migration is typically thought to be an evolved trait driven by responses to forage or predation, but recent studies have demonstrated avoidance of parasitism can also affect success of migratory tactics within a population. We evaluated hypotheses of how migration alters parasite exposure in a partially migratory elk (Cervus canadensis) population in and adjacent to Banff National Park, Alberta, Canada. Equal numbers of elk remain year-round on the winter range or migrate to summer range. We quantified diversity and abundance of parasites in faecal elk pellets, and prevalence (number of infected individuals) and intensity (egg counts) of giant liver fluke eggs (Fascioloides magna) in faeces across migratory tactics. We tested whether giant liver fluke intensity in faeces was affected by elk use of wetlands, elevation, forage biomass, and elk concentration in the previous summer. We rejected the "migratory escape" hypothesis that suggests migration allowed elk to escape parasite exposure because migrant elk had the highest richness and evenness of parasite groups. We also rejected the hypothesis that prevalence was highest at highest summer densities because higher-density resident elk had the lowest diversity and giant liver fluke egg presence and intensity. Instead, the high prevalence and intensity of giant liver flukes in migrants was consistent with both the hypothesis of "environmental tracking", because elk that migrated earlier may expose themselves to favourable parasite conditions, and with the "environmental sampling" hypothesis, because giant liver fluke intensity increased with increased exposure to secondary host habitat (i.e., wetland). Our results indicate that differential exposure of different migratory tactics that leave the winter range has a greater influence on parasites than the concentration of elk that reside on the winter range year-round.

Integrating livestock management and telemetry data to assess disease transmission risk between wildlife and livestock

Overlap of cattle and wild elk ranges in southwestern Alberta foothills is an opportunity for inter-species interactions. To assess the spatio-temporal patterns of disease transmission risk between cattle and elk, several risk indexes were defined to represent different transmission routes. Risk indexes were estimated by combining elk telemetry data obtained from 168 GPS-collared elk, and cattle management information obtained by interviews conducted in 16 cow-calf operations overlapping the elk home range. We assessed the bias resulting from ignoring cattle movement related to seasonnal grazing practices, and the impact of the assessment of spatio-temporal patterns of risk. Direct transmission risk indexes peaked during winter months, due to aggregation at higher densities of both elk and cattle on winter ranges and winter pastures, respectively. However, a summer peak also was observed when risk indexes were not adjusted for pasture area, due to larger cattle summer pastures overlapping a higher number of elk telemetry locations. We identified periods when the proximity of elk to specific features (such as mineral blocks, hay land, winter-feeding areas, or water sources) may increase the risk of inter-species transmission. Indirect transmission risk indexes increased with the survival of pathogens in the environment, as the temporal constraint for cattle and elk overlap decreased. Finally, integrating pasture management information substantially influenced the magnitude and temporal patterns of transmission risk indexes, highlighting the importance of collecting detailed livestock management data in the context of assessing the risk of inter-species disease transmission.

Accelerated onset of chronic wasting disease in elk (Cervus canadensis) vaccinated with a PrPSc-specific vaccine and housed in a prion contaminated environment

Chronic wasting disease (CWD) is a fatal prion disease affecting multiple cervid species. Effective management tools for this disease, particularly in free-ranging populations, are currently limited. We evaluated a novel CWD vaccine in elk (Cervus canadensis) naturally exposed to CWD through a prion-contaminated environment. The vaccine targets a YYR disease-specific epitope to induce antibody responses specific to the misfolded (PrP^Sc) conformation. Female elk calves (n = 41) were captured from western Wyoming and transported to the Thorne-Williams Wildlife Research Center where CWD has been documented since 1979. Elk were held in contaminated pens for 14 to 20 days before being alternately assigned to either a vaccine (n = 21) or control group (n = 20). Vaccinated animals initially received two vaccinations approximately 42 days apart and annual vaccinations thereafter. Vaccination induced elevated YYR-specific antibody titers in all animals. Elk were genotyped for the prion protein gene at codon 132, monitored for clinical signs of CWD through daily observation, for disease status through periodic biopsy of rrectoanal mucosa-associated lympoid tissue (RAMALT), and monitored for YYR-specific serum antibody titres. Mean survival of vaccinated elk with the 132MM genotype (n = 15) was significantly shorter (800 days) than unvaccinated elk (n = 13) of the same genotype (1062 days; p = 0.003). Mean days until positive RAMALT biopsy for 132MM vaccinated elk (6 7 8) were significantly shorter than unvaccinated 132MM elk (990; p = 0.012). There was, however, no significant difference in survival between vaccinated (n = 4) and control (n = 5) elk with the 132ML genotype (p = 0.35) or in timing of positive RAMALT biopsies of 132ML elk (p = 0.66). There was no strong (p = 0.17) correlation between YYR-specific antibody titers and survival time. Determining the mechanism by which this vaccine accelerates onset of CWD will be important to direct further CWD vaccine research.

Hidden cost of disease in a free-ranging ungulate: brucellosis reduces mid-winter pregnancy in elk

Demonstrating disease impacts on the vital rates of free-ranging mammalian hosts typically requires intensive, long-term study. Evidence for chronic pathogens affecting reproduction but not survival is rare, but has the potential for wide-ranging effects. Accurately quantifying disease-associated reductions in fecundity is important for advancing theory, generating accurate predictive models, and achieving effective management. We investigated the impacts of brucellosis (Brucella abortus) on elk (Cervus canadensis) productivity using serological data from over 6,000 captures since 1990 in the Greater Yellowstone Ecosystem, USA. Over 1,000 of these records included known age and pregnancy status. Using Bayesian multilevel models, we estimated the age-specific pregnancy probabilities of exposed and naïve elk. We then used repeat-capture data to investigate the full effects of the disease on life history. Brucellosis exposure reduced pregnancy rates of elk captured in mid- and late-winter. In an average year, we found 60% of exposed 2-year-old elk were pregnant compared to 91% of their naïve counterparts (a 31 percentage point reduction, 89% HPDI = 20%-42%), whereas exposed 3- to 9-year-olds were 7 percentage points less likely to be pregnant than naïve elk of their same age (89% HPDI = 2%-11%). We found these reduced rates of pregnancy to be independent from disease-induced abortions, which afflict a portion of exposed elk. We estimate that the combination of reduced pregnancy by mid-winter and the abortions following mid-winter reduces the reproductive output of exposed female elk by 24%, which affects population dynamics to a similar extent as severe winters or droughts. Exposing hidden reproductive costs of disease is essential to avoid conflating them with the effects of climate and predation. Such reproductive costs cause complex population dynamics, and the magnitude of the effect we found should drive a strong selection gradient if there is heritable resistance.

CATTLE ( BOS TAURUS) RESIST CHRONIC WASTING DISEASE FOLLOWING ORAL INOCULATION CHALLENGE OR TEN YEARS' NATURAL EXPOSURE IN CONTAMINATED ENVIRONMENTS

We conducted a 10-yr study to establish whether chronic wasting disease (CWD) was readily transmissible to domestic cattle ( Bos taurus) following oral inoculation or by cohousing cattle with captive cervids in outdoor research facilities where CWD was enzootic. Calves ( n=12) were challenged orally on one occasion using brain homogenate derived from CWD-infected mule deer ( Odocoileus hemionus). Five uninoculated cattle served as unchallenged controls. Two other groups of cattle ( n=10-11/group) were housed outdoors for 10 yr in captive cervid research facilities. The environmentally challenged cattle were exposed to CWD-associated prions through common paddocks, feed, and water and via direct daily contact with known and potentially infected mule deer or wapiti ( Cervus canadensis) throughout the decade-long study period. None of the exposed cattle developed neurologic disease during the study. We euthanized cattle surviving to 10 yr postchallenge and examined all for lesions or disease-associated prion protein (PrP^d) by histopathology, immunohistochemistry, and western immunoblot analysis of central nervous system and lymphoid tissue. None had evidence of PrP^d accumulation. We conclude that the risks of CWD transmission to cattle following oral inoculation or after prolonged exposure to contaminated environments are low.

An expanding population of the giant liver fluke (Fascioloides magna) in elk (Cervus canadensis) and other ungulates in Canada

Giant liver fluke (Fascioloides magna) populations readily expand under suitable conditions. Although extirpated from the eastern slopes of the Canadian Rocky Mountains in the early 1960s, the fluke reappeared following natural spread through mountain passes from British Columbia. Herein, we assessed epizootiology of the fluke population two decades later. Between 1984 and 1991, 534 ungulates, including 381 elk (Cervus canadensis), 68 mule deer (Odocoileus hemionus hemionus), 54 white-tailed deer (Odocoileus virginianus), and 31 moose (Alces alces) from adjacent areas of Alberta (AB) and British Columbia (BC), Canada, were examined for giant liver flukes. Prevalence in elk increased from 53% to 79% (1984-91) in Banff National Park (BNP) in AB and 77% to 100% (1985-89) in Kootenay National Park (KNP) in BC. Super-infections (>100 flukes) were more common in later years. Generally, prevalence increased over time and with increasing age of elk. Intensity was lowest in young-of-year (BNP 8±5, KNP 3), but similar in yearlings (BNP 36±11, KNP 23±8) and adults (BNP 33±5, KNP 32±6). Prevalence was similar in male and female elk. Intensity was higher in males (BNP 47±7, KNP 46±12) than in females (BNP 28±6, KNP 22±4), although the maximum number of flukes (545) occurred in a female elk. Prevalence and intensity differed among other species of ungulates but patterns were similar in each park. Prevalence was lower in mule deer (BNP 6%, KNP 4%) than in white-tailed deer (BNP 44%, KNP 28%) and moose (BNP 52%, KNP 63%). Intensity differed among these species but never exceeded 30 flukes. Gravid flukes occurred only in elk and white-tailed deer. Transmission occurred primarily in late summer-fall and in wet habitats. At least seven elk died as a direct result of fluke infection. In this region, elk and white-tailed deer maintain the F. magna population with spillover into moose and, rarely, mule deer.