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USGS2010

Deer carcass decomposition and potential scavenger exposure to chronic wasting disease

Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy afflicting the Cervidae family in North America, causing neurodegeneration and ultimately death. Although there are no reports of natural cross-species transmission of CWD to noncervids, infected deer carcasses pose a potential risk of CWD exposure for other animals. We placed 40 disease-free white-tailed deer (Odocoileus virginianus) carcasses and 10 gut piles in the CWD-affected area of Wisconsin (USA) from September to April in 2003 through 2005. We used photos from remotely operated cameras to characterize scavenger visitation and relative activity. To evaluate factors driving the rate of carcass removal (decomposition), we used KaplanMeier survival analysis and a generalized linear mixed model. We recorded 14 species of scavenging mammals (6 visiting species) and 14 species of scavenging birds (8 visiting species). Prominent scavengers included American crows (Corvus brachyrhynchos), raccoons (Procyon lotor), and Virginia opossums (Didelphis virginiana). We found no evidence that deer consumed conspecific remains, although they visited gut piles more often than carcasses relative to temporal availability in the environment. Domestic dogs, cats, and cows either scavenged or visited carcass sites, which could lead to human exposure to CWD. Deer carcasses persisted for 18 days to 101 days depending on the season and year, whereas gut piles lasted for 3 days. Habitat did not influence carcass decomposition, but mammalian and avian scavenger activity and higher temperatures were positively associated with faster removal. Infected deer carcasses or gut piles can serve as potential sources of CWD prions to a variety of scavengers. In areas where surveillance for CWD exposure is practical, management agencies should consider strategies for testing primary scavengers of deer carcass material.

Journal of Wildlife Management↗

USGS2015

Context-dependent survival, fecundity and predicted population-level consequences of brucellosis in African buffalo

Chronic infections may have negative impacts on wildlife populations, yet their effects are difficult to detect in the absence of long-term population monitoring. Brucella abortus , the bacteria responsible for bovine brucellosis, causes chronic infections and abortions in wild and domestic ungulates, but its impact on population dynamics is not well understood. We report infection patterns and fitness correlates of bovine brucellosis in African buffalo based on (1) 7 years of cross-sectional disease surveys and (2) a 4-year longitudinal study in Kruger National Park (KNP), South Africa. We then used a matrix population model to translate these observed patterns into predicted population-level effects. Annual brucellosis seroprevalence ranged from 8·7% (95% CI = 1·8–15·6) to 47·6% (95% CI = 35·1–60·1) increased with age until adulthood (>6) and varied by location within KNP. Animals were on average in worse condition after testing positive for brucellosis ( F = −5·074, P < 0·0001), and infection was associated with a 2·0 (95% CI = 1·1–3·7) fold increase in mortality (χ 2 = 2·039, P = 0·036). Buffalo in low body condition were associated with lower reproductive success ( F = 2·683, P = 0·034), but there was no association between brucellosis and pregnancy or being observed with a calf. For the range of body condition scores observed in the population, the model-predicted growth rate was λ = 1·11 (95% CI = 1·02–1·21) in herds without brucellosis and λ = 1·00 (95% CI = 0·85–1·16) when brucellosis seroprevalence was 30%. Our results suggest that brucellosis infection can potentially result in reduced population growth rates, but because these effects varied with demographic and environmental conditions, they may remain unseen without intensive, longitudinal monitoring.

Kruger National Park↗

USGS2009

Disease, predation and demography: Assessing the impacts of bovine tuberculosis on African buffalo by monitoring at individual and population levels

Summary Understanding the effects of disease is critical to determining appropriate management responses, but estimating those effects in wildlife species is challenging. We used bovine tuberculosis (BTB) in the African buffalo Syncerus caffer population of Kruger National Park, South Africa, as a case study to highlight the issues associated with estimating chronic disease effects in a long‐lived host. We used known and radiocollared buffalo, aerial census data, and a natural gradient in pathogen prevalence to investigate if: (i) at the individual level, BTB infection reduces reproduction; (ii) BTB infection increases vulnerability to predation; and (iii) at the population level, increased BTB prevalence causes reduced population growth. There was only a marginal reduction in calving success associated with BTB infection, as indexed by the probability of sighting a known adult female with or without a calf ( P = 0·065). Since 1991, BTB prevalence increased from 27 to 45% in the southern region and from 4 to 28% in the central region of Kruger National Park. The prevalence in the northern regions was only 1·5% in 1998. Buffalo population growth rates, however, were neither statistically different among regions nor declining over time. Lions Panthera leo did not appear to preferentially kill test‐positive buffalo. The best (Akaike's Information Criterion corrected for small sample size) AIC c model with BTB as a covariate [exp(β) = 0·49; 95% CI = (0·24–1·02)] suggested that the mortality hazard for positive individuals was no greater than for test‐negative individuals. Synthesis and applications . Test accuracy, time‐varying disease status, and movement among populations are some of the issues that make the detection of chronic disease impacts challenging. For these reasons, the demographic impacts of bovine tuberculosis in the Kruger National Park remain undetectable despite 6 years of study on known individuals and 40 years of population counts. However, the rainfall and forage conditions during this study were relatively good and the impacts of many chronic diseases may be a non‐linear function of environmental conditions such that they are only detectable in stressful periods.

Kruger National Park↗

USGS2026

Disease-associated mortality drives reduction in Yukon River Chinook salmon escapement: A novel method for quantifying the negative impacts of ‘misfit’ parasites to improve fisheries management

Parasites can suppress host populations through parasite-induced mortality. However, the negative effects of parasites are difficult to measure in wild populations and we have few tools for quantifying the magnitude of parasite-induced mortality. This is especially true for many ‘misfit’ parasites that do not fit into standard classifications (e.g. fungal-like parasites and myxozoans). As such, we are limited in our ability to include the effects of parasites in fish and wildlife management strategies. Chinook salmon ( Oncorhynchus tshawytscha ) are a species of immense cultural and ecological significance but populations are declining across much of their range. In the Yukon River, Alaska, USA, episodic outbreaks of the ichthyosporean parasite Ichthyophonus have been linked to declines, but population-level effects of Ichthyophonus on Yukon Chinook salmon remain largely unknown. We developed a novel model that leverages changes in parasite intensity distributions to quantify the magnitude of disease-induced mortality occurring in host populations. We used it to address two questions to inform management of Yukon Chinook salmon: (i) Is parasite-induced mortality occurring in Chinook salmon and at what magnitude? (ii) What are the drivers of spatio-temporal variability in parasite-induced mortality? Using 3 years of surveys, we quantified the evidence for the presence, magnitude, and variability in Ichthyophonus -induced mortality in Chinook salmon. Our model predicted that Ichthyophonus was responsible for between 8% and 15% mortality of the migrating Chinook salmon population prior to reaching the Canadian border and could describe nearly 35% of unaccounted for mortality at the border. The model predicted that variability in mortality among years could largely be explained by differences in parasite acquisition in the marine environment rather than differences in infection dynamics in the river. Synthesis and applications . Alaska Department of Fish and Game is implementing an annual monitoring program at the mouth of the Yukon River where our model will estimate the proportion of fish at risk from parasite-induced mortality to inform annual management. Moreover, the model is broadly applicable to other fungal-like and myxozoan parasites of conservation concern, where improved estimates of parasite-induced mortality could be used to predict parasite suppression of wild and managed host populations.

Alaska↗

USGS2013

Pregnancy rates in central Yellowstone bison

Plains bison ( Bison b. bison ) centered on Yellowstone National Park are chronically infected with brucellosis ( Brucella abortus ) and culled along the park boundaries to reduce the probability of disease transmission to domestic livestock. We evaluated the relationship between pregnancy rates and age, dressed carcass weight, and serological status for brucellosis among bison culled from the central Yellowstone subpopulation during the winters of 1996–1997, 2001–2002, and 2002–2003. A model with only dressed carcass weight was the best predictor of pregnancy status for all ages with the odds of pregnancy increasing by 1.03 (95% CI = 1.02–1.04) for every 1-kg increase in weight. We found no effect of age or the serological status for brucellosis on pregnancy rates across age classes; however, we did find a positive association between age and pregnancy rates for bison ≥2 years old. Bison ≥2 years old had an overall pregnancy rate of 65% with markedly different rates in alternate ages for animals between 3 and 7 years old. Pregnancy rates were 0.50 (95% CI = 0.31–0.69) for brucellosis positive and 0.57 (95% CI = 0.34–0.78) for brucellosis negative 2- and 3-year-olds and 0.74 (95% CI = 0.60–0.85) in brucellosis positive and 0.69 (95% CI = 0.49–0.85) in brucellosis negative bison ≥4 years old. Only 1 of 21 bison <2 years old was pregnant. Our findings are important to accurately predict the effects of brucellosis on Yellowstone bison population dynamics. We review our results relative to other studies of Yellowstone bison that concluded serological status for brucellosis influences pregnancy rates.

Wyoming↗

USGS2023

Rapid prototyping for quantifying belief weights of competing hypotheses about emergent diseases

Emerging diseases can have devastating consequences for wildlife and require a rapid response. A critical first step towards developing appropriate management is identifying the etiology of the disease, which can be difficult to determine, particularly early in emergence. Gathering and synthesizing existing information about potential disease causes, by leveraging expert knowledge or relevant existing studies, provides a principled approach to quickly inform decision-making and management efforts. Additionally, updating the current state of knowledge as more information becomes available over time can reduce scientific uncertainty and lead to substantial improvement in the decision-making process and the application of management actions that incorporate and adapt to newly acquired scientific understanding. Here we present a rapid prototyping method for quantifying belief weights for competing hypotheses about the etiology of disease using a combination of formal expert elicitation and Bayesian hierarchical modeling. We illustrate the application of this approach for investigating the etiology of stony coral tissue loss disease (SCTLD) and discuss the opportunities and challenges of this approach for addressing emergent diseases. Lastly, we detail how our work may apply to other pressing management or conservation problems that require quick responses. We found the rapid prototyping methods to be an efficient and rapid means to narrow down the number of potential hypotheses, synthesize current understanding, and help prioritize future studies and experiments. This approach is rapid by providing a snapshot assessment of the current state of knowledge. It can also be updated periodically (e.g., annually) to assess changes in belief weights over time as scientific understanding increases. Synthesis and applications: The rapid prototyping approaches demonstrated here can be used to combine knowledge from multiple experts and/or studies to help with fast decision-making needed for urgent conservation issues including emerging diseases and other management problems that require rapid responses. These approaches can also be used to adjust belief weights over time as studies and expert knowledge accumulate and can be a helpful tool for adapting management decisions.

Journal of Environmental Management↗

USGS2013

Estimating transmission of avian influenza in wild birds from incomplete epizootic data: implications for surveillance and disease spreac

Estimating disease transmission in wildlife populations is critical to understand host–pathogen dynamics, predict disease risks and prioritize surveillance activities. However, obtaining reliable estimates for free-ranging populations is extremely challenging. In particular, disease surveillance programs may routinely miss the onset or end of epizootics and peak prevalence, limiting the ability to evaluate infectious processes. We used profile likelihood to estimate the force of infection (FOI) in a low pathogenic avian influenza virus (LPAIv) epizootic model from censored time series of LPAIv prevalence in hatch-year waterfowl (order Anseriformes) at postbreeding and migration sites in North America. We found a mean LPAIv FOI of 0·12 day −1 [95% CI, 0·00–0·39], corresponding to an incidence rate of 0·11 day −1 , with geographic heterogeneity (min–max: 0·02–0·23 day −1 ) among study sites. These high infection rates indicate that most hatch-year waterfowl are likely infected with LPAIv early in the fall migration. Comparison of model-predicted and observed immunity confirmed our assumption of naïve hatch-year waterfowl and suggested long-term immunity (>6 months) for adults. Using the mean LPAIv incidence rate, we predict a shorter and lower epizootic curve for highly pathogenic avian influenza virus (HPAIv; 5 weeks with peak prevalence of 28% and 30% mortality) than LPAIv (8 weeks with peak prevalence of 50%). These findings indicate it is harder to detect HPAIv than LPAIv with swabs from live birds, which are commonly used during disease surveillance. Synthesis and applications . Our study highlights the potential of integrating incomplete surveillance data with epizootic models to quantify disease transmission and immunity. This modelling approach provides an important tool to understand spatial and temporal epizootic dynamics and inform disease surveillance. Our findings suggest focusing highly pathogenic avian influenza virus (HPAIv) surveillance on postbreeding areas where mortality of immunologically naïve hatch-year birds is most likely to occur, and collecting serology to enhance HPAIv detection. Our modelling approach can integrate various types of disease data facilitating its use with data from other surveillance programs (as illustrated by the estimation of infection rate during an HPAIv outbreak in mute swans Cygnus olor in Europe).

Journal of Applied Ecology↗

USGS2021

Negligible evidence for detrimental effects of Leucocytozoon infections among Emperor Geese (Anser canagicus) breeding on the Yukon-Kuskokwim Delta, Alaska

Emperor Geese ( Anser canagicus ) are iconic waterfowl endemic to Alaska and adjacent areas of northeastern Russia that are considered to be near threatened by the International Union for Conservation. This species has been identified as harboring diverse viruses and parasites which have, at times, been associated with disease in other avian taxa. To better assess if disease represents a vulnerability for Emperor Geese breeding on the Yukon-Kuskokwim Delta, Alaska, we evaluated if haemosporidian parasites were associated with decreased mass or survival among adult female nesting birds captured during 2006–2016. Through molecular analyses, we detected genetically diverse Leucocytozoon , Haemoproteus , and Plasmodium parasites in 28%, 1%, and 1% of 607 blood samples screened in triplicate, respectively. Using regression analysis, we found evidence for a small effect of Leucocytozoon infection on the mass of incubating adult female Emperor Geese. The estimated mass of infected individuals was approximately 43 g (95% CI: 20–67 g), or approximately 2%, less than uninfected birds when captured during the second half of incubation (days 11–25). We did not, however, find support for an effect of Leucocytozoon infection on survival of adult female nesting Emperor Geese using a multi-state hidden Markov framework to analyze mark-resight and recapture data. Using parasite mitochondrial DNA cytochrome b sequences, we identified 23 haplotypes among infected Emperor Geese. Leucocytozoon haplotypes clustered into three phylogenetically supported clades designated as ‘ L. simondi clade A’, ‘ L. simondi clade B’, and ‘other Leucocytozoon ’. We did not find evidence that parasites assigned to any of these clades were associated with differential mass measures among nesting adult female Emperor Geese. Collectively, our results provide negligible evidence for Leucocytozoon parasites as causing detrimental effects to adult female Emperor Geese breeding on the Yukon-Kuskokwim Delta.

Alaska↗

USGS2014

Contrasting past and current numbers of bears visiting Yellowstone cutthroat trout streams

Spawning cutthroat trout ( Oncorhynchus clarkii bouvieri ) were historically abundant within tributary streams of Yellowstone Lake within Yellowstone National Park and were a highly digestible source of energy and protein for Yellowstone’s grizzly bears ( Ursus arctos ) and black bears ( U. americanus ). The cutthroat trout population has subsequently declined since the introduction of non-native lake trout (Salvelinus namaycush), and in response to effects of drought and whirling disease ( Myxobolus cerebralis ). The trout population, duration of spawning runs, and indices of bear use of spawning streams had declined in some regions of the lake by 1997–2000. We initiated a 3-year study in 2007 to assess whether numbers of spawning fish, black bears, and grizzly bears within and alongside stream corridors had changed since 1997– 2000. We estimated numbers of grizzly bears and black bears by first compiling encounter histories of individual bears visiting 48 hair-snag sites along 35 historically fished streams.We analyzed DNA encounter histories with Pradel-recruitment and Jolly-Seber (POPAN) capture-mark-recapture models. When compared to 1997–2000, the current number of spawning cutthroat trout per stream and the number of streams with cutthroat trout has decreased. We estimated that 48 (95% CI¼42–56) male and 23 (95% CI¼21–27) female grizzly bears visited the historically fished tributary streams during our study. In any 1- year, 46 to 59 independent grizzly bears (8–10% of estimated Greater Yellowstone Ecosystem population) visited these streams. When compared with estimates from the 1997 to 2000 study and adjusted for equal effort, the number of grizzly bears using the stream corridors decreased by 63%. Additionally, the number of black bears decreased between 64% and 84%. We also document an increased proportion of bears of both species visiting front-country (i.e., near human development) streams. With the recovery of cutthroat trout, we suggest bears that still reside within the Lake basin will readily use this high-quality food resource.

Journal of Wildlife Management↗

USGS1995

Spring-staging ecology of midcontinent greater white-fronted geese

A major part of the midcontinent greater white-fronted goose ( Anser albifrons ) population stages for several weeks in spring in the Rainwater Basin Area (RBA) of south-central Nebraska where substantial mortality from disease occurs periodically. Effective management of this population requires better data on use of habitat, vulnerability to disease, and the role of staging areas in migration and reproduction. We studied use of habitat, foods, nutrient dynamics, and effect of changes in agriculture on food availability and habitat needs in spring 1979-80. During daylight, geese were observed primarily in harvested cornfields (76%) and growing winter wheat (23%). Corn grain and winter wheat shoots composed 90 and 9%, respectively, of foods consumed by collected geese ( n = 42). Feeding activity did not vary among post-harvest cornfield treatments except that little feeding occurred ( P < 0.05) in moldboard-plowed fields (<1%). Fat content for all geese increased ( P ≤ 0.01) with Julian date; protein content increased ( P = 0.03) only among adult females, and there was no evidence ( P > 0.05) of temporal variation in calcium content. Adult geese storing 14.2 g of fat per day deposited approximately 582 g of fat between 22 February and 8 April. Energy requirements for thermal regulation were small compared with requirements for fat synthesis and probably had little effect on nutrient deposition. The 34,000 white-fronted geese present on the Harvard Marsh and Prairie Dog Marsh study areas in March 1980 probably used <20% of the corn available within a 5-km radius. We believe that midcontinent white-fronted geese arrive on Arctic breeding grounds with larger and less variable fat reserves than prior to modern agricultural development. We attribute this response to increased food availability on staging areas where the net effect of agricultural changes has been an increase in corn availability. Waterfowl managers can increase dispersion of geese and provide favorable foraging conditions by maintaining well-distributed wetland roosting habitat and by working with private landowners to ensure access to grain in the vicinity of wetlands.

Nebraska↗

USGS2025

Trophic transfer of fipronil residues to black-footed ferrets: Implications for ferret safety, flea control, and plague mitigation

Sylvatic plague, caused by the flea-borne bacterium Yersinia pestis , is an invasive disease in North America that causes reductions of native fauna and transforms ecosystems. Fipronil baits have shown promise in reducing flea loads on prairie dogs Cynomys spp. for plague mitigation. Many species depend on prairie dogs and their ecological influences, including the black-footed ferret Mustela nigripes (ferret), an obligate predator of prairie dogs. To better understand how fipronil affects ferrets, we offered carcass portions from black-tailed prairie dogs C. ludovicianus that had consumed fipronil bait (0.005% fipronil by weight) to captive ferrets and monitored their health. We fed carcass portions of three prairie dogs to four adult ferrets for 1 week. No ill effects were observed in the ferrets. We collected scat from the ferrets before, during, and after their feeding on treated prairie dogs. We evaluated potential effects of ferret scat on larval fleas, which feed on organic matter. Fipronil residues were not detected in ferret scat samples collected before treatment. During and shortly after treatment, ferret scat contained 3.76 ng/g fipronil and 13.75 ng/g fipronil sulfone, on average, demonstrating trophic transfer of the residues from prey to predator. We presented 0.5 mg of ferret scat to each of 96 larval Oropsylla montana (Siphonaptera: Ceratophyllidae) and assessed survival rates over 24 h. When exposed to ferret scat lacking fipronil residues, 85% of larvae survived. Survival was reduced to 61% and 35% for larvae contacting or consuming scat with fipronil-residue, respectively. Fipronil residues in scat from a variety of species on prairie dog colonies, perhaps especially the prairie dogs, may assist in flea control and plague mitigation. Hosts eliminate fipronil residues, and fipronil residues in the environment degrade over time, reducing but not eliminating potential concerns with bioaccumulation.

Journal of Fish and Wildlife Management↗

USGS2017

Paltry past-precipitation: Predisposing prairie dogs to plague?

The plague bacterium Yersinia pestis was introduced to California in 1900 and spread rapidly as a sylvatic disease of mammalian hosts and flea vectors, invading the Great Plains in the United States by the 1930s to 1940s. In grassland ecosystems, plague causes periodic, devastating epizootics in colonies of black-tailed prairie dogs ( Cynomys ludovicianus ), sciurid rodents that create and maintain subterranean burrows. In doing so, plague inhibits prairie dogs from functioning as keystone species of grassland communities. The rate at which fleas transmit Y. pestis is thought to increase when fleas are abundant. Flea densities can increase during droughts when vegetative production is reduced and herbivorous prairie dogs are malnourished and have weakened defenses against fleas. Epizootics of plague have erupted frequently in prairie dogs during years in which precipitation was plentiful, and the accompanying cool temperatures might have facilitated the rate at which fleas transmitted Y. pestis . Together these observations evoke the hypothesis that transitions from dry-to-wet years provide conditions for plague epizootics in prairie dogs. Using generalized linear models, we analyzed a 24-year dataset on the occurrence of plague epizootics in 42 colonies of prairie dogs from Colorado, USA, 1982–2005. Of the 33 epizootics observed, 52% erupted during years with increased precipitation in summer. For the years with increased summer precipitation, if precipitation in the prior growing season declined from the maximum of 502 mm to the minimum of 200 mm, the prevalence of plague epizootics was predicted to increase 3-fold. Thus, reduced precipitation may have predisposed prairie dogs to plague epizootics when moisture returned. Biologists sometimes assume dry conditions are detrimental for plague. However, 48% of epizootics occurred during years in which precipitation was scarce in summer. In some cases, an increased abundance of fleas during dry years might compensate for other conditions that become less favorable for plague transmission. Global warming is forecasted to amplify the hydrological cycle in the Great Plains, causing an increased occurrence of prolonged droughts interceded by brief periods of intense precipitation. Results herein suggest these changes might affect plague cycles in prairie dogs. Both negative and positive consequences of dry conditions should be considered when managing plague.

Journal of Wildlife Management↗

USGS2015

Estimating the phenology of elk brucellosis transmission with hierarchical models of cause-specific and baseline hazards

Understanding the seasonal timing of disease transmission can lead to more effective control strategies, but the seasonality of transmission is often unknown for pathogens transmitted directly. We inserted vaginal implant transmitters (VITs) in 575 elk ( Cervus elaphus canadensis ) from 2006 to 2014 to assess when reproductive failures (i.e., abortions or still births) occur, which is the primary transmission route of Brucella abortus , the causative agent of brucellosis in the Greater Yellowstone Ecosystem. Using a survival analysis framework, we developed a Bayesian hierarchical model that simultaneously estimated the total baseline hazard of a reproductive event as well as its 2 mutually exclusive parts (abortions or live births). Approximately, 16% (95% CI = 0.10, 0.23) of the pregnant seropositive elk had reproductive failures, whereas 2% (95% CI = 0.01, 0.04) of the seronegative elk had probable abortions. Reproductive failures could have occurred as early as 13 February and as late as 10 July, peaking from March through May. Model results suggest that less than 5% of likely abortions occurred after 6 June each year and abortions were approximately 5 times more likely in March, April, or May compared to February or June. In western Wyoming, supplemental feeding of elk begins in December and ends during the peak of elk abortions and brucellosis transmission (i.e., Mar and Apr). Years with more snow may enhance elk-to-elk transmission on supplemental feeding areas because elk are artificially aggregated for the majority of the transmission season. Elk-to-cattle transmission will depend on the transmission period relative to the end of the supplemental feeding season, elk seroprevalence, population size, and the amount of commingling. Our statistical approach allowed us to estimate the probability density function of different event types over time, which may be applicable to other cause-specific survival analyses. It is often challenging to assess the cause of death, or in this case whether the reproductive event was an abortion or live birth. Accounting for uncertainty in the event type is an important future addition to our methodological approach.

Wyoming↗

USGS2015

Modeling risk of pneumonia epizootics in bighorn sheep

Pneumonia epizootics are a major challenge for management of bighorn sheep ( Ovis canadensis ) affecting persistence of herds, satisfaction of stakeholders, and allocations of resources by management agencies. Risk factors associated with the disease are poorly understood, making pneumonia epizootics hard to predict; such epizootics are thus managed reactively rather than proactively. We developed a model for herds in Montana that identifies risk factors and addresses biological questions about risk. Using Bayesian logistic regression with repeated measures, we found that private land, weed control using domestic sheep or goats, pneumonia history, and herd density were positively associated with risk of pneumonia epizootics in 43 herds that experienced 22 epizootics out of 637 herd-years from 1979–2013. We defined an area of high risk for pathogen exposure as the area of each herd distribution plus a 14.5-km buffer from that boundary. Within this area, the odds of a pneumonia epizootic increased by >1.5 times per additional unit of private land (unit is the standardized % of private land where global  = 25.58% and SD = 14.53%). Odds were >3.3 times greater if domestic sheep or goats were used for weed control in a herd's area of high risk. If a herd or its neighbors within the area of high risk had a history of a pneumonia epizootic, odds of a subsequent pneumonia epizootic were >10 times greater. Risk greatly increased when herds were at high density, with nearly 15 times greater odds of a pneumonia epizootic compared to when herds were at low density. Odds of a pneumonia epizootic also appeared to decrease following increased spring precipitation (odds = 0.41 per unit increase, global  = 100.18% and SD = 26.97%). Risk was not associated with number of federal sheep and goat allotments, proximity to nearest herds of bighorn sheep, ratio of rams to ewes, percentage of average winter precipitation, or whether herds were of native versus mixed or reintroduced origin. We conclude that factors associated with risk of pneumonia epizootics are complex and may not always be from the most obvious sources. The ability to identify high-risk herds will help biologists and managers determine where to focus management efforts and the risk factors that most affect each herd, facilitating more effective, proactive management.

Journal of Wildlife Management↗