Historical, current, and potential population size estimates of invasive wild pigs (Sus scrofa) in the United States

Miller R.S., Opp S.M., Webb C.T.

Tabak M.A., Webb C.T., Miller R.S.

Population dynamics of species that are recently introduced into a new area, e.g., invasive species and species of conservation concern that are translocated to support global populations, are likely to be dominated by short-term, transient effects. Wild pigs (Sus scrofa, or wild boar) are pulsed-resource consumers of mast nuts that are commonly introduced into new areas. We used vital rate data (i.e., survival and fecundity) for wild pigs in Germany under varying forage conditions to simulate transient population dynamics in the 10-years following introduction into a new environment. In a low forage environment (i.e., conditions similar to their native range), simulated wild pig populations maintained a stable population size with low probability of establishment, while in environments with better quality forage (i.e., conditions similar to parts of their invasive range), high juvenile fecundity and survival facilitated rapid population growth and establishment probability was high. We identified a strategy for simulating population dynamics of species whose reproduction and survival depend on environmental conditions that fluctuate and for predicting establishment success of species introduced into a new environment. Our approach can also be useful in projecting near-term transient population dynamics for many conservation and management applications.

Hernández F.A., Parker B.M., Pylant C.L., Smyser T.J., Piaggio A.J., Lance S.L., Milleson M.P., Austin J.D., Wisely S.M.

Wild pigs (Sus scrofa) are the most widely distributed invasive wild ungulate in the United States, yet the factors that influence wild pig dispersal and colonization at the regional level are poorly understood. Our objective was to use a population genetic approach to describe patterns of dispersal and colonization among populations to gain a greater understanding of the invasion process contributing to the expansion of this species. We used 52 microsatellite loci to produce individual genotypes for 482 swine sampled at 39 locations between 2014 and 2016. Our data revealed the existence of genetically distinct subpopulations (F ST  = 0.1170, p < 0.05). We found evidence of both fine-scale subdivision among the sampling locations, as well as evidence of long term genetic isolation. Several locations exhibited significant admixture (interbreeding) suggesting frequent mixing of individuals among locations; up to 14% of animals were immigrants from other populations. This pattern of admixture suggested successive rounds of human-assisted translocation and subsequent expansion across Florida. We also found evidence of genetically distinct populations that were isolated from nearby populations, suggesting recent introduction by humans. In addition, proximity to wild pig holding facilities was associated with higher migration rates and admixture, likely due to the escape or release of animals. Taken together, these results suggest that human-assisted movement plays a major role in the ecology and rapid population growth of wild pigs in Florida.

Corn J.L., Jordan T.R.

The Southeastern Cooperative Wildlife Disease Study developed the first national feral swine (Sus scrofa) map for the United States in 1982 in collaboration with state wildlife resources agencies. National feral swine distribution maps were completed in 1982, 1988, and 2004 as individual maps, and then annually beginning in 2008 through the National Feral Swine Mapping System (NFSMS). The NFSMS is an internet-based data-collection website used in collaboration with state wildlife resources agencies and the U.S. Department of Agriculture, Animal and Plant Health Inspection Service. These ongoing collaborations have provided for a long-term database that documents the expansion of established feral swine populations in the United States. The number of states reporting established populations was 18 in 1982 and 35 in 2016. The geographic area included in the distribution of feral swine increased from 544,854 km2 in 1982 to 1,675,618 km2 in 2016. We describe the development of the national feral swine maps including details on how these data were collected; provide feral swine maps for select years from 1982 to 2016; and note some of the uses of these maps. These maps detail the expansion of feral swine since 1982, which can be used in the future to monitor increases or decreases in the distribution of feral swine as natural reproduction of feral swine continues and feral swine control programs are implemented. © 2017 The Wildlife Society.

Miller R.S., Sweeney S.J., Slootmaker C., Grear D.A., Di Salvo P.A., Kiser D., Shwiff S.A.

Cross-species disease transmission between wildlife, domestic animals and humans is an increasing threat to public and veterinary health. Wild pigs are increasingly a potential veterinary and public health threat. Here we investigate 84 pathogens and the host species most at risk for transmission with wild pigs using a network approach. We assess the risk to agricultural and human health by evaluating the status of these pathogens and the co-occurrence of wild pigs, agriculture and humans. We identified 34 (87%) OIE listed swine pathogens that cause clinical disease in livestock, poultry, wildlife, and humans. On average 73% of bacterial, 39% of viral, and 63% of parasitic pathogens caused clinical disease in other species. Non-porcine livestock in the family Bovidae shared the most pathogens with swine (82%). Only 49% of currently listed OIE domestic swine diseases had published wild pig surveillance studies. The co-occurrence of wild pigs and farms increased annually at a rate of 1.2% with as much as 57% of all farms and 77% of all agricultural animals co-occurring with wild pigs. The increasing co-occurrence of wild pigs with livestock and humans along with the large number of pathogens shared is a growing risk for cross-species transmission.

Tabak M.A., Piaggio A.J., Miller R.S., Sweitzer R.A., Ernest H.B.

Humans are playing an increasingly large role in the expansion of invasive species' distributions, but few (if any) studies have evaluated anthropogenic factors associated with intentional translocation of invasives. The wild pig (Sus scrofa) is an extremely destructive and rapidly expanding invasive species whose movement is thought to be facilitated by humans. We sought to (1) identify a suite of genetic markers that can be applied to population genetic analyses of wild pigs, (2) find quantitative evidence of human-mediated dispersal of wild pigs, and (3) determine which anthropogenic factors were associated with their translocation. We identified 43 polymorphic microsatellite loci and employed population genetic analyses to evaluate population structure and movement of wild pigs among populations in California, USA. Hierarchical Bayesian models were used to evaluate the influence of anthropogenic covariates on wild pig movement, and to predict migration risk. Natural dispersal of wild pigs among populations was low, as indicated by a large number of genetic clusters (K = 21), significant population differentiation, and low rates of recent migration. This suggests that the observed movement resulted from human-mediated translocation. Movement of pigs was positively predicted by the number of domestic pig farms, the number of captive game hunting farms, the amount of public land, the number of wild pigs harvested by hunters, and the number of game outfitters. While hunting has been hypothesized to play a role in wild pig movement, our study is the first to provide quantitative evidence of such a relationship. We argue that future efforts to manage invasive species must consider the potential role of humans in their dispersal.

Lewis J.S., Farnsworth M.L., Burdett C.L., Theobald D.M., Gray M., Miller R.S.

Biotic and abiotic factors are increasingly acknowledged to synergistically shape broad-scale species distributions. However, the relative importance of biotic and abiotic factors in predicting species distributions is unclear. In particular, biotic factors, such as predation and vegetation, including those resulting from anthropogenic land-use change, are underrepresented in species distribution modeling, but could improve model predictions. Using generalized linear models and model selection techniques, we used 129 estimates of population density of wild pigs (Sus scrofa) from 5 continents to evaluate the relative importance, magnitude, and direction of biotic and abiotic factors in predicting population density of an invasive large mammal with a global distribution. Incorporating diverse biotic factors, including agriculture, vegetation cover, and large carnivore richness, into species distribution modeling substantially improved model fit and predictions. Abiotic factors, including precipitation and potential evapotranspiration, were also important predictors. The predictive map of population density revealed wide-ranging potential for an invasive large mammal to expand its distribution globally. This information can be used to proactively create conservation/management plans to control future invasions. Our study demonstrates that the ongoing paradigm shift, which recognizes that both biotic and abiotic factors shape species distributions across broad scales, can be advanced by incorporating diverse biotic factors.

Snow N.P., Jarzyna M.A., VerCauteren K.C.

Summary The eruption of invasive wild pigs (IWPs) Sus scrofa throughout the world exemplifies the need to understand the influences of exotic and nonnative species expansions. In particular, the continental USA is precariously threatened by a rapid expansion of IWPs, and a better understanding of the rate and process of spread can inform strategies that will limit the expansion. We developed a spatially and temporally dynamic model to examine three decades (1982–2012) of IWP expansion, and predict the spread of IWPs throughout the continental USA, relative to where IWPs previously inhabited. We used the model to predict where IWPs are likely to invade next. The average rate of northward expansion increased from 6·5 to 12·6 km per year, suggesting most counties in the continental USA could be inhabited within the next 3–5 decades. The spread of IWPs was primarily associated with expansion into areas with similar environmental characteristics as their previous range, with the exception of spreading into colder regions. We identified that climate change may assist spread into northern regions by generating milder winters with less snow. Otherwise, the spread of IWPs was not dependent on agriculture, precipitation or biodiversity at the county level. The model correctly predicted 86% of counties that were invaded during 2012, and those predictions indicate that large portions of the USA are in immediate danger of invasion. Synthesis and applications. Anti-invasion efforts should focus along the boundaries of current occupied range to stop natural expansion, and anti-invasion policies should focus on stopping anthropogenic transport and release of invasive wild pigs. Our results demonstrate the utility of a spatio-temporal examination to inform strategies for limiting the spread of invasive wild pigs.

Anderson A., Slootmaker C., Harper E., Holderieath J., Shwiff S.A.

We report the results of one of the most comprehensive surveys on feral swine ( Sus scrofa ) damage and control in 11 US states (Alabama, Arkansas, California, Florida, Georgia, Louisiana, Mississippi, Missouri, North Carolina, South Carolina and Texas). The survey was distributed by the USDA National Agricultural Statistical Service in the summer of 2015 to a sample of producers of corn ( Zea mays ), soybeans ( Glycine max ), wheat ( Triticum ), rice ( Oryza sativa ), peanuts ( Arachis hypogaea ), and sorghum ( Sorghum bicolor ) in the 11-state region. Producers that failed to respond to the initial mailing received multiple follow-up phone calls in an attempt to minimize non-response bias, and a total of 4377 responses were obtained. Findings indicate that damage can be substantial. The highest yield loss estimates occur in peanut and corn production in the Southeast and Texas. Control efforts are common, and producers incur considerable costs from shooting and trapping efforts. Extrapolating crop damage estimates to the state-level in 10 states with reportable damage yields an estimated crop loss of $190 million. Though large, this number likely represents only a small fraction of the total damage by feral swine in the 10 states because it only includes crop damage to six crops. We hope findings from this survey will help guide control efforts and research, as well as serve as a benchmark against which the effectiveness of future control efforts can be measured.

Street G.M., Rodgers A.R., Avgar T., Vander Vennen L.M., Fryxell J.M.

Habitat-based prediction of population density relies on relationships between landscape configuration (i.e., abundance of land-cover types) and equilibrium density. This may be accomplished by estimating resource selection probability functions (RSPFs) based on presence–absence data, or by relating carrying capacity to landscape covariates. We used RSPFs for moose (Alces alces) from 2 study sites and carrying capacities from 34 wildlife management units across northern Ontario, Canada, to create 2 estimators of moose density. We compared the predictions of both models to moose density in a novel site obtained via aerial census. We also projected the RSPF across 34 management units and compared predicted density to estimated carrying capacity of each unit. The RSPF and carrying capacity models predicted moose equilibrium densities that were statistically indistinguishable from the estimated density of moose at the novel study site, but the carrying capacity model generated uninformatively broad prediction intervals. The RSPF failed to predict carrying capacities in management units across Ontario; however, the differences between RSPF estimates and carrying capacities varied predictably with differences in covariates related to forage availability, suggesting habitat selection strength and RSPF transferability vary with landscape quality. Estimating densities using RSPFs relies on a consistent relationship between habitat selection and animal density; thus, RSPF applicability across space will depend heavily on similarity between the novel and original sites. Demographic projection benefits from broad spatiotemporal datasets that improve reliability but that are relatively rare and subject to broad error. Our findings suggest that selection-based population estimation is preferable to demographically based models because of increased precision of estimates, the immediacy of available data (e.g., single survey or radio-telemetry in multiple sites vs. many generations of population estimates in a time series across space), and the capacity to predict fine-scale patterns of distribution and abundance. © 2016 The Wildlife Society.

Davis A.J., Hooten M.B., Miller R.S., Farnsworth M.L., Lewis J., Moxcey M., Pepin K.M.

Evaluation of the progress of management programs for invasive species is crucial for demonstrating impacts to stakeholders and strategic planning of resource allocation. Estimates of abundance before and after management activities can serve as a useful metric of population management programs. However, many methods of estimating population size are too labor intensive and costly to implement, posing restrictive levels of burden on operational programs. Removal models are a reliable method for estimating abundance before and after management using data from the removal activities exclusively, thus requiring no work in addition to management. We developed a Bayesian hierarchical model to estimate abundance from removal data accounting for varying levels of effort, and used simulations to assess the conditions under which reliable population estimates are obtained. We applied this model to estimate site-specific abundance of an invasive species, feral swine (Sus scrofa), using removal data from aerial gunning in 59 site/time-frame combinations (480-19,600 acres) throughout Oklahoma and Texas, USA. Simulations showed that abundance estimates were generally accurate when effective removal rates (removal rate accounting for total effort) were above 0.40. However, when abundances were small (

Early R., Bradley B.A., Dukes J.S., Lawler J.J., Olden J.D., Blumenthal D.M., Gonzalez P., Grosholz E.D., Ibañez I., Miller L.P., Sorte C.J., Tatem A.J.

Invasive alien species (IAS) threaten human livelihoods and biodiversity globally. Increasing globalization facilitates IAS arrival, and environmental changes, including climate change, facilitate IAS establishment. Here we provide the first global, spatial analysis of the terrestrial threat from IAS in light of twenty-first century globalization and environmental change, and evaluate national capacities to prevent and manage species invasions. We find that one-sixth of the global land surface is highly vulnerable to invasion, including substantial areas in developing economies and biodiversity hotspots. The dominant invasion vectors differ between high-income countries (imports, particularly of plants and pets) and low-income countries (air travel). Uniting data on the causes of introduction and establishment can improve early-warning and eradication schemes. Most countries have limited capacity to act against invasions. In particular, we reveal a clear need for proactive invasion strategies in areas with high poverty levels, high biodiversity and low historical levels of invasion. Globalization facilitates the spread of invasive alien species, while environmental change can ease invasion. Here, Early et al. identify vulnerable regions globally and evaluate capacity in vulnerable countries to prevent invasions arising from sources such as air travel, horticulture, and pet trade.

Keiter D.A., Mayer J.J., Beasley J.C.

Sus scrofa is both a destructive invasive species and a popular game animal in many parts of the world, but there is a lack of consistency and accuracy in how scientists and wildlife managers refer to wild-living members of the species. The growing importance of this invasive species necessitates that scientists, managers, and policy-makers standardize use of a common name in a taxonomically accurate manner to effectively communicate to the general public and scientific community. In this commentary, we discuss the current terminology used for S. scrofa and, based upon the history of introductions of this species, propose that these animals be referred to as wild pigs within their introduced range unless it is known that the population consists of genetically pure wild boar or domestic pigs that have recently been released and become feral. Use of the term “wild pig” should reduce the potential to misclassify populations as a result of genetic introgression and evolution following release. Furthermore, we recommend that, when appropriate, the terms “nonnative” or “invasive” be included to describe wild pigs in their introduced range to emphasize their negative impacts on natural and anthropogenic environments. The effective control of wild pig populations considered to be invasive will require informed public support and sound scientific management, necessitating clear communication about this species among the research community, wildlife managers, and the general public. © 2016 The Wildlife Society.

Frauendorf M., Gethöffer F., Siebert U., Keuling O.

The wild boar population has increased enormously in all of Europe over the last decades and caused problems like crop damage, transmission of diseases, and vehicle accidents. Therefore, it is necessary to investigate the underlying causes of this increase in order to be able to manage populations effectively. The purpose of this study was to analyse how environmental (food and climate) and physiological factors (maternal weight and age) as well as hunting and population density influence the litter size of wild boar populations in Northern Germany. The mean litter size in the studied population for the whole period was 6.6 (range 1–12), which is one of the highest in all of Europe. Litter size was positively influenced by maternal body weight, higher mast yield of oak as well as higher temperature in combination with higher precipitation in summer. Only higher temperature or only higher precipitation in summer however had a negative effect on litter size production. Probably,weather and food conditions act via maternal bodyweight on the litter size variation in wild boar. Hunting as well a s population density did not affect the litter size variation in this study which might indicate that wild boar population did not reach carrying capacity yet.

McClure M.L., Burdett C.L., Farnsworth M.L., Lutman M.W., Theobald D.M., Riggs P.D., Grear D.A., Miller R.S.

Wild pigs (Sus scrofa), also known as wild swine, feral pigs, or feral hogs, are one of the most widespread and successful invasive species around the world. Wild pigs have been linked to extensive and costly agricultural damage and present a serious threat to plant and animal communities due to their rooting behavior and omnivorous diet. We modeled the current distribution of wild pigs in the United States to better understand the physiological and ecological factors that may determine their invasive potential and to guide future study and eradication efforts. Using national-scale wild pig occurrence data reported between 1982 and 2012 by wildlife management professionals, we estimated the probability of wild pig occurrence across the United States using a logistic discrimination function and environmental covariates hypothesized to influence the distribution of the species. Our results suggest the distribution of wild pigs in the U.S. was most strongly limited by cold temperatures and availability of water, and that they were most likely to occur where potential home ranges had higher habitat heterogeneity, providing access to multiple key resources including water, forage, and cover. High probability of occurrence was also associated with frequent high temperatures, up to a high threshold. However, this pattern is driven by pigs’ historic distribution in warm climates of the southern U.S. Further study of pigs’ ability to persist in cold northern climates is needed to better understand whether low temperatures actually limit their distribution. Our model highlights areas at risk of invasion as those with habitat conditions similar to those found in pigs’ current range that are also near current populations. This study provides a macro-scale approach to generalist species distribution modeling that is applicable to other generalist and invasive species.

Bradley E.A., Lockaby B.G., Madere S., Bolds S., Kalin L., Ditchkoff S.S., Brown V.R.

AbstractThe range and density of one of North America's most destructive and invasive mammalian species, wild pigs (Sus scrofa), has expanded rapidly over the past several decades. Alongside this growth, their fecal contamination of surface waters has impaired water quality through significantly increased levels of pathogenic bacteria, raising concerns over the potential for zoonotic disease transmission. Significant remediation of these water quality impacts has been shown as a result of reductions in wild pig populations due to control efforts; however, the duration of these remediation effects as populations rebound remains unclear. Our study sought to determine the longevity of water quality remediation resulting from wild pig population control efforts. We found that median concentrations of Escherichia coli and fecal coliform (CFU/100 mL) increased by 746% and 159% in the year following the conclusion of removal efforts, resulting in median concentrations of 79% and 159% greater than those observed prior. We also found increased public health risk, with samples exceeding E. coli and fecal coliform guidelines 10% and 12% more often than pre‐removal, respectively. While further research into wild pig population dynamics and fecal contamination is necessary, we conclude that ongoing population control efforts may be necessary to remediate water quality impacts and public health risks associated with invasive wild pigs.

Walker H.L., Miller R.S., Pomeroy L.W., Arruda A.G.

Taylor C.R., Buxton L., Beasley J.C.

AbstractWild pigs (Sus scrofa) are one of the most ecologically harmful invasive vertebrates globally. Due to their negative impacts, wild pig populations are managed via trapping, yet studies investigating various trap designs have been limited in duration, location, and number of trappers. Using data from professional trappers across the southeastern U.S., we evaluated the performance of 3 wild pig trap types (corral, drop, passive net), and the effect of forage season (barren, green‐up, masting) on trapping success. Specifically, we compared trap effectiveness (estimated proportion of targeted wild pigs caught per capture event), trap night effort (number of days to first catch), and the amount of bait and time used per individual take over the lifetime of each trap location across the 3 trap types and forage seasons. Across >850 capture events by 31 trappers, all 3 trap types evaluated were effective at capturing entire social groups of wild pigs. Few differences were observed among trap types, although drop traps in masting season captured a greater estimated proportion of wild pigs per capture event compared to other trap type‐season combinations. Our data also revealed that passive net traps required slightly more bait/wild pig captured than drop traps but there was no difference in the time/wild pig captured among traps. Our findings demonstrate that when operated by wildlife professionals, multiple designs of wild pig traps can be effective at removing targeted groups of wild pigs. Further, our results offer insights regarding the performance of wild pig trap types across seasons that can be used to inform wild pig trapping programs.

Kanes D., Malagon D., Camper B., Hewitt A., Dunn S., Purcell E., Bewick S.

ABSTRACTThe Asian Needle Ant, Brachyponera chinensis (Hymenoptera: Formicidae), has spread throughout a substantial portion of the southeastern United States where it has primarily been restricted to low elevations. We focused on the B. chinensis invasion in Great Smoky Mountains National Park (GSMNP). Records in and near the park represent some of the highest elevation locations of B. chinensis in North America. The goals of this study were to characterize the status of the B. chinensis invasion in GSMNP, to assess the role that disturbance and human visitation play in B. chinensis invasion within GSMNP, to identify the potential of B. chinensis to spread into higher elevations in the park and the southern Appalachians and to determine the impact that this might have on native species, including keystone seed‐dispersers within the Aphaenogaster rudis complex and their myrmecochorous plants. We surveyed GSMNP for B. chinensis at 45 sites, including sites that were burned during the 2016 Gatlinburg fire, sites with high human visitation, and undisturbed sites. We then built species distribution models (SDMs) for B. chinensis and some of the native species that B. chinensis is most likely to impact. This allowed us to assess the potential for high‐elevation refugia within the southern Appalachians. We did not find B. chinensis at any undisturbed sites in GSMNP. We did find B. chinensis at five high‐visitation sites. Field findings were consistent with our SDMs, which suggested that GSMNP's unique precipitation regimes may act as a barrier to invasion. Unfortunately, SDMs indicated moderate suitability for B. chinensis across a sizable proportion of the northern border of the park. This is a region where B. chinensis may have disproportionate impacts on myrmecochorous plant species. Thus, although southern Appalachian precipitation and temperature regimes may provide a refuge from B. chinensis at high elevations, this will not protect all species likely to be impacted by this invasive ant.

Gaya H.E., D’Angelo G.J., Vukovich M., Youngmann J.L., Lance S.L., Kilgo J.C.

Context Control of invasive wild pigs (Sus scrofa) is a growing management concern throughout their invaded range. In the United States, control programs often leave wild pig carcasses on the landscape where they are freely available for consumption by scavengers such as coyotes (Canis latrans). Coyotes consume wild pigs, but no studies have investigated the importance of pig carcasses for maintaining coyote abundance. Aims We tested the hypothesis that coyote populations may be bolstered by wild pig carcasses created by control programs. Methods From July 2014 to July 2017, we surveyed road transects for scat to monitor coyote abundance in response to changing levels of pig carcass availability. From June 2015 to July 2017, wild pigs were removed from the eastern half of the study area and placed at one of four carcass dump sites on the western side. We analysed the scat data using an open population spatially-explicit capture–mark recapture model to estimate seasonal abundance and movement of coyotes in response to the carcass treatment. Results Coyote density across the entire study area declined from 95 coyotes/100 km2 in July 2014 to 65 coyotes/100 km2 by July 2016, but declines were unrelated to the carcass availability treatment. Additional analysis on non-genotyped scat data showed no apparent effect of carcass availability on coyote density. Coyote activity centers moved fewer than 100 m towards the nearest carcass dump site in response to the carcass treatment. Conclusions Wild pig carcass availability is not likely to be a primary driver of coyote abundance or territory selection at the study location. Implications We conclude that the availability of wild pig carcasses has little effect on coyote abundance and thus wild pig carcass removal will not be an effective coyote management strategy.

Chalkowski K., Pepin K., Lavelle M., Miller R., Fischer J., Brown V., Glow M., Smith B., Cook S., Kohen K., Sherburne S., Smith H., Leland B., VerCauteren K., Snow N.

Snow N.P., Smith B., Lavelle M.J., Glow M.P., Chalkowski K., Leland B.R., Sherburne S., Fischer J.W., Kohen K.J., Cook S.M., Smith H., VerCauteren K.C., Miller R.S., Pepin K.M.

Introductions of transboundary animal diseases (TADs) into free-ranging wildlife can be difficult to control and devastating for domestic livestock trade. Combating a new TAD introduction in wildlife with an emergency response requires quickly limiting spread of the disease by intensely removing wild animals within a contiguous area. In the case of African swine fever virus (ASFv) in wild pigs (Sus scrofa), which has been spreading in many regions of the world, there is little information on the time- and cost-efficiency of methods for intensively and consistently culling wild pigs and recovering carcasses in an emergency response scenario. We compared the efficiencies of aerial operations, trapping, experimental toxic baiting, and ground shooting in northcentral Texas, USA during two months in 2023. Culling and recovering carcasses of wild pigs averaged a rate of 0.15 wild pigs/person hour and cost an average of $233.04/wild pig ($USD 2023) across all four methods. Aerial operations required the greatest initial investment but subsequently was the most time- and cost-efficient, costing an average of $7266 to reduce the population by a standard measure of 10 %, including recovering carcasses. Aerial operations required a ground crew of ∼7 people/helicopter to recover carcasses. Costs for reducing the population of wild pigs using trapping were similar, although took 13.5 times longer to accomplish. In cases where carcass recovery and disposal are needed (e.g., response to ASFv), a benefit of trapping was immediate carcass recovery. Toxic baiting was less efficient because both culling and carcass recovery required substantial time. We culled very few wild pigs with ground shooting in this landscape. Our results provide insight on the efficiencies of each removal method. Strategically combining removal methods may increase overall efficiency. Overall, our findings inform the preparation of resources, personnel needs, and deployment readiness for TAD responses involving wild pigs.

Parsons M.A., Vercauteren K.C., Dellinger J.A., Young J.K.

Wild pigs (Sus scrofa) are an introduced species that affect ecosystems through myriad pathways. They are the target of population control efforts, but one outstanding question is the extent to which native predators affect population demography. Cougars (Puma concolor) are a known predator of wild pigs and cooccur with wild pigs in several regions of the Americas. However, investigations of wild pig survival in regions with cougars are lacking. We investigated the survival and causes of mortality for wild pigs in California, USA where cougars could act as a predator. We also explored habitat selection of wild pigs with respect to cougar predation risk. We collared 69 wild pigs, 15 adults, 15 subadults, and 39 juveniles. Captures occurred in winter and spring and survival estimates primarily reflect spring and summer survival. We estimated 6-month survival of adults and juveniles to be 0.923 (95% confidence interval: 0.789–1.00) and 0.563 (0.416–0.762), respectively, which are similar to estimates from areas without cougars. Only juvenile and one subadult wild pig were killed by cougars, suggesting that cougars are a limited predator of adults. We also investigated feeding locations of 3 GPS-collared cougars to generate a spatial layer of cougar kill occurrence. We used this layer in an integrated step selection function for wild pigs and observed wild pigs selecting areas with low probability of cougar kill occurrence during times when cougars are most active. Combined, these results suggest that cougars are a minor source of mortality for wild pigs during the spring and summer and may be unlikely to provide substantial biological resistance against the spread of wild pigs. Our monitoring occurred when native prey (e.g. ungulate neonates) are most abundant which may influence cougar predation of pigs. It is likely that a preference for native prey, the novelty of wild pigs, wild pig habitat selection, and the potential danger of adult wild pigs reduces cougar predation.

Canino N., Torhorst C., Botero‐Cañola S., Beati L., O'Hara K.C., James A., Wisely S.M.

AbstractThe soft tick Ornithodoros turicata Duges (Acari: Argasidae) is a potential vector of African swine fever virus (ASFV). We evaluated the efficacy of two methods to collect soft ticks rapidly and efficiently from gopher tortoise (Gopherus polyphemus) burrows, which are ubiquitous throughout large regions of the southeastern United States and their burrows are a known microhabitat of O. turicata. Burrow vacuuming was an effective and efficient tick collection method; no tick was captured employing CO2 trapping. Using an occupancy modelling framework, we estimated that the probability of detecting ticks from an infested burrow each time a sample was taken with this method was 58% and increased with the average relative humidity. With the occupancy model, we estimated that 70% of the burrows in the study area were infested with O. turicata. Manual sifting of the burrow material yielded more ticks (6.6 individuals/sample) than using a set of three sieves (2.9 individuals/sample), yet the probability of detecting the species was not different between the two methods (Pval = 0.7). These methods can inform the development of ASF vector surveillance and outbreak response plans in areas of high risk for ASFV introduction in the region.

McDonough M.T., Zenas S.J., Gitzen R.A., Smith M.D., VerCauteren K.C., Ditchkoff S.S.

AbstractThere is insufficient understanding of interspecific interactions with the eastern wild turkey (Meleagris gallopavo silvestris) and wild pigs (Sus scrofa). Wild pigs compete with wild turkeys and predate nests and adults; however, population‐level effects on wild turkeys are not clear. Using cameras, we assessed responses of wild turkey populations to wild pig removal in central Alabama, USA, from 2018–2021. We compared wild turkey relative abundance and occupancy on 3 large‐scale pig‐removal treatment sites (3,407–5,531 ha) relative to a control site (2,510 ha) during 1 pre‐treatment year and 2 post‐treatment years, with analyses including a covariate expressing the cumulative number of pigs removed from each site standardized by the initial pig abundance on the site. We removed 1,851 wild pigs from the 3 treatment sites over 22 months. Based on N‐mixture modeling, when the number of pigs removed was equal to our baseline population estimates (i.e., 100% removal relative to initial population), there were 1.50 (95% CL = 1.01–2.23) times as many wild turkeys, and detection of wild turkeys was 2.01 (95% CL = 1.49–2.70) times as likely. Additionally, poults were 3.49 (95% CL = 1.12–10.89) times as likely to occupy an area when the number of pigs removed was equal to our baseline population estimates compared with poult occupancy at baseline pig abundance. Our data suggests that reduction of wild pig populations may lead to a localized increase in populations of wild turkeys.

Humphreys J.M., Pelzel-McCluskey A.M., Shults P.T., Velazquez-Salinas L., Bertram M.R., McGregor B.L., Cohnstaedt L.W., Swanson D.A., Scroggs S.L., Fautt C., Mooney A., Peters D.P., Rodriguez L.L.

Vesicular stomatitis (VS) is a vector-borne livestock disease caused by the vesicular stomatitis New Jersey virus (VSNJV). This study presents the first application of an SEIR-SEI compartmental model to analyze VSNJV transmission dynamics. Focusing on the 2014–2015 outbreak in the United States, the model integrates vertebrate hosts and insect vector demographics while accounting for heterogeneous competency within the populations and observation bias in documented disease cases. Key epidemiological parameters were estimated using Bayesian inference and Markov chain Monte Carlo (MCMC) methods, including the force of infection, effective reproduction number (Rt), and incubation periods. The model revealed significant underreporting, with only 10–24% of infections documented, 23% of which presented with clinical symptoms. These findings underscore the importance of including competence and imperfect detection in disease models to depict outbreak dynamics and inform effective control strategies accurately. As a baseline model, this SEIR-SEI implementation is intended to serve as a foundation for future refinements and expansions to improve our understanding of VS dynamics. Enhanced surveillance and targeted interventions are recommended to manage future VS outbreaks.

Giglio R.M., Bowden C.F., Brook R.K., Piaggio A.J., Smyser T.J.

AbstractGlobalization has led to the frequent movement of species out of their native habitat. Some of these species become highly invasive and capable of profoundly altering invaded ecosystems. Feral swine (Sus scrofa × domesticus) are recognized as being among the most destructive invasive species, with populations established on all continents except Antarctica. Within the United States (US), feral swine are responsible for extensive crop damage, the destruction of native ecosystems, and the spread of disease. Purposeful human‐mediated movement of feral swine has contributed to their rapid range expansion over the past 30 years. Patterns of deliberate introduction of feral swine have not been well described as populations may be established or augmented through small, undocumented releases. By leveraging an extensive genomic database of 18,789 samples genotyped at 35,141 single nucleotide polymorphisms (SNPs), we used deep neural networks to identify translocated feral swine across the contiguous US. We classified 20% (3364/16,774) of sampled animals as having been translocated and described general patterns of translocation using measures of centrality in a network analysis. These findings unveil extensive movement of feral swine well beyond their dispersal capabilities, including individuals with predicted origins >1000 km away from their sampling locations. Our study provides insight into the patterns of human‐mediated movement of feral swine across the US and from Canada to the northern areas of the US. Further, our study validates the use of neural networks for studying the spread of invasive species.

Pinto M.D., Neto J.A., de Freitas M.J., Florentino B.F., de Souza Sapatera N., Paiva F., Nakamura A.A., Rozza D.B., Lucheis S.B., Bresciani K.D.

Although previous studies have characterized the helminth fauna of wild boars kept in captivity in Brazil, records on these helminths in free-ranging animals are still scarce. In view of this, we aimed in our work to investigate the occurrence and morphological and morphometric characteristics of gastrointestinal helminths in wild Sus scrofa from the northwest region of the State of São Paulo, Brazil. The digestive systems of 10 animals (5 males and 5 females of different ages) were used in this study. Each anatomical segment was washed and sieved under running water, and the helminths were separated and identified using light and scanning electron microscopy, according to their morphological characteristics. A total of 2750 (1152 males and 1598 females) nematode specimens were collected from the small intestine of these wild boars, and all of them presented the morphological characteristics of Globocephalus urosubulatus. However, one characteristic is of particular interest because it has not yet been reported in the literature: a marked asymmetry between the lobes and their respective rays of the copulatory bursa, with the left one being larger than the right one. In this research, we identified the presence of G. urosubulatus in all the examined free-ranging wild boars and reported for the first time in the literature the asymmetry in the copulatory bursa.

Snow N.P., Smith B., Lavelle M., Glow M., Chalkowski K., Leland B., Sherburne S., Fischer J., Kohen K., Cook S., Smith H., VerCauteren K.C., Miller R., Pepin K.

AbstractIntroductions of foreign animal diseases (FADs) into free-ranging wildlife can be difficult to control and devastating for domestic livestock trade. Combating a new FAD introduction in wildlife with an emergency response requires quickly limiting spread of the disease by intensely removing wild animals and recovering their carcasses for proper disposal. In the case of African swine fever virus (ASFv) in wild pigs (Sus scrofa), which has been spreading in many regions of the world, there is little information on the time- and cost-efficiency of methods for intensively and consistently removing wild pigs and recovering carcasses in an emergency response scenario. We compared the efficiencies of aerial operations, trapping, an experimental toxic bait, and ground shooting in northcentral Texas, USA during two months in 2023. Removing and recovering carcasses of wild pigs averaged a rate of 0.15 wild pigs/person hour and cost an average of $233.04/wild pig ($USD 2023) across all four methods. Aerial operations required the greatest initial investment but subsequently was the most time- and cost-efficient, costing an average of $7,266 to incrementally reduce the population by 10% including recovering carcasses. Aerial operations required a ground crew of ∼7 people/helicopter to recover carcasses. Costs for reducing the population of wild pigs using trapping were similar, although took 13.5 times longer to accomplish. A benefit of trapping was carcass recovery was incorporated. Toxic baiting was less efficient because carcass recovery required substantial time, and we removed very few wild pigs with ground shooting in this landscape. We recommend combining aerial and trapping methodologies to remove wild pigs and their carcasses efficiently and effectively during a FAD response. Overall, our findings can inform the preparation of resources, personnel needs, and deployment readiness for FAD responses involving wild pigs.

Brown M.E., Miller D.L., Smith A.N., Cory B.M.

Feral hogs (Sus scrofa) are invasive, ecosystem engineers and a novel disturbance to rare, fire-dependent, herbaceous wetland ecosystems in Florida, USA. Their feeding activity uproots vegetation, altering plant composition and continuity. Hog rooting can also create linked disturbance by ingesting vegetation critical for fire spread. Herbaceous communities are vulnerable to shrub encroachment when fire return intervals are increased. We examined the impact of hog rooting intensity (% uprooted vegetation) on the resilience of herbaceous, seepage wetland vegetation cover and composition and the effect of hog rooting on fire spread. We hypothesized that (1) vegetation cover and composition would reflect initial intensity of hog rooting and remain altered with and without additional rooting, and (2) reduction of foliar cover by feral hog rooting would reduce fire spread. Total foliar cover, functional group cover, richness, and cover of plant genera were estimated in plots subjected to three intensity levels of hog rooting then appraised inside and outside of exclosures for 7 years. Spatial data was collected to compare areas with and without damage from hogs to areas burned by prescribed fires from 2010–2013. Total foliar cover was reduced for 5 years with high intensity hog rooting compared to no-low intensity rooting. Cover of a keystone, bunchgrass species was reduced with high intensity hog rooting. With repeated rooting, total and graminoid foliar cover were reduced outside exclosures. Fire spread was significantly reduced in areas of hog rooting. These findings have broader implications for conservation of other fire-maintained herbaceous communities impacted by nonindigenous feral hogs.