Wild Pig Ecology & Management

Wild pigs (Sus scrofa) are a highly invasive species that are rapidly expanding in number and distribution throughout the U.S. It is estimated that wild pig populations now exceed 5 million animals in the U.S. alone, causing billions of dollars in ecological and agricultural damages annually. In addition, vehicle collisions with wild pigs represent a growing threat to human safety. Despite the significant ecological and economic impact of expanding wild pig populations, few tools are available to effectively control the rapid spread of this invasive species. Moreover, although estimates of abundance are a central component of any species management program, reliable estimators for free-ranging pig populations are limited due to a number of ecological and economic factors.

SPATIAL ECOLOGY, POPULATION DYNAMICS, AND DISEASE DYNAMICS OF WILD PIGS ON THE SAVANNAH RIVER SITE

SREL Collaborators: Jim Beasley, Sarah Chinn, Lindsay Clontz

Outside Collaborators: Kurt VerCauteren (USDA-APHIS), Kim Pepin (USDA-APHIS), Raoul Boughton (U. Florida), Sam Wisely (U. Florida), Amy Davis (USDA-APHIS), Tim Smyser (USDA-APHIS), John Kilgo (USFS), Toni Piaggio (USDA-APHIS)

We are working with researchers at the USDA-APHIS-WS-National Wildlife Research Center, the University of Florida, and the USFS on a number of studies to better understand wild pig ecology and improve management of this invasive species. In particular, we are currently conducting studies to elucidate the spatial, genetic, and disease associations of local pig populations, both within and among sounders. Using modern trapping techniques that facilitate sampling of entire sounders we are able to assess the fine-scale structure and disease dynamics within pig populations at the level of individual sounders. These data coupled with information on the movement behavior of each sampled sounder will be used to develop and refine analytical models to predict the spread of pig populations as well as the dissemination of infectious diseases of concern to human or livestock health. We also are using an extensive network of GPS collars deployed on sounders to better understand both inter- and intra-group movement behavior, and how such behavior can influence disease transmission dynamics. Such data are critically needed to evaluate and refine the efficacy of control methods to facilitate management of wild pigs in the U.S. and other regions where this species is invasive.

PATTERNS OF AGRICULTURAL AND ENVIRONMENTAL DAMAGE BY WILD PIGS, AND EVALUATION OF CHANGES IN WILD PIG POPULATIONS AND DAMAGE IN RESPONSE TO MANAGEMENT

SREL Collaborators: NRCS, APHIS, Kurt VerCauteren (USDA-APHIS), SCDNR, Newberry County Soil and Water Conservation District, Jasper County Soil and Water Conservation District

Invasive species can cause extensive damage to native and agricultural ecosystems upon establishment. As the population and range of wild pigs (Sus scrofa) continues to grow across North America, managers are faced with the mounting challenge of maximizing the efficiency of control and monitoring efforts with limited resources. However, there are currently few published data on the spatial and temporal characteristics of wild pig damage to both native and agricultural systems as well as wild pig responses to management. This study aims to better understand patterns of wild pig damage to resources, as well as influence of removal efforts on wild pig population size and extent of damages to both agriculture and native ecosystems. We are conducting walked ground transects and unmanned aerial systems (UAS) multi-spectral imagery to identify and quantify damage to corn and peanut fields in SC. In addition, we are quantifying changes wild pig populations, environmental damage, and agricultural damage in conjunction with USDA-WS wild pig control efforts on private lands in SC. This research will ultimately improve management strategies to help reduce the impacts of wild pigs on our native ecosystems, livestock, crops, and human health.

ASSESSMENT OF VEHICLE COLLISION LOCATIONS WITH WILD PIGS

SREL Collaborators: Jim Beasley

Outside Collaborators: Jack Mayer (SRNL)

Vehicle collisions with wild pigs are a growing issue that has received surprisingly little attention, despite the fact that there have been numerous human fatalities associated with pig-vehicle collisions. At the Savannah River Site alone between 30 and 40 pigs are struck by vehicles each year, despite an intensive management program to control the pig population on site. We are currently using a combination of pig movement data and known collision locations to better predict where collisions are likely to occur so that appropriate mitigation strategies can be developed to reduce the number and severity of vehicle collisions with pigs. These data represent some of the only data on pig-vehicle collision locations and thus are an important step forward in reducing human-wildlife conflicts associated with this species.

ESTIMATION OF WILD PIGLET SURVIVAL RATES

SREL Collaborators: Jim Beasley, Dave Keiter, Sarah Chinn, Allie Rakowski

Outside Collaborators: John Kilgo (USFS), Mark Vukovich (USFS)

In addition to reproduction, survival is an important driver of population models. Survival can fluctuate with age, size, season, landscape characteristics, resource availability, and genetics. While adult survival is relatively high and constant, juvenile survival may be more sensitive to density dependence. Although recent studies have emphasized the importance of juvenile recruitment in wild pigs to population growth, little research has been performed to estimate piglet survival in their introduced range: vital information for modeling pig population dynamics. We are conducting the first radio-telemetry study of wild piglet survival in the introduced range of this species, investigating survival as a function of multiple demographic and environmental factors. Upon farrowing, we will locate the nest and capture, tag, weigh and count the neonate piglets for subsequent real-time survival monitoring for at least 4 weeks, a period of time during which there are no robust survival data for neonate piglets. Increased knowledge of piglet survival rates through performance of a known-fate study may facilitate management of this species and development of more informed population projection models, and therefore help reduce the growth of destructive wild pig populations.

MATERNAL INVESTMENT AND LITTER SEX RATIO

SREL Collaborators: Jim Beasley, Sarah Chinn

Outside Collaborators: Tim Smyser (USDA-APHIS)

Female condition has been proposed as a significant driver of offspring sex ratio. The Triver’s Willard Model (TWM, 1973) is an ecological theory that predicts that high-quality mothers should invest more into sons because males have higher variance in individual fitness (i.e., reproduction). Thus, females should be able to adjust their offspring sex ratio in response to factors that could modify both their own lifetime reproductive success and the reproductive success of their progeny. It is not well defined if TWM applies to, or how it applies to polytocous species, those that produce several offspring per litter. We are collecting data on the sex ratio of wild pig litters through samples obtained from necropsied pregnant sows as well as live captured litters collected for survival monitoring. We are using these data to determine the extent to which maternal characteristics, environmental factors, and genetics affect the sex composition of wild pig litters.

FARROWING ECOLOGY: HABITAT USE AND RESOURCE SELECTION

SREL Collaborators: Jim Beasley, Sarah Chinn, Allie Rakowski

Outside Collaborators: John Kilgo (USFS)

Little is understood about farrowing ecology such as nest site selection or resource use during pregnancy for wild pigs. We are investigating how sow movements change between pre-parturition, parturition, and post-parturition by fitting pregnant sows with GPS collars and a vaginal implant transmitters (VIT) that signal the exact timing of the birth event as well as the location of the farrowing nest. We also are collecting nest characteristics such as dimensions, shape, building materials used, and local habitat attributes. These data will be used to better understand the farrowing ecology of this species, as well as to develop predictive models to elucidate parturition events for sows that are collared but deployed with a VIT.

REPRODUCTIVE ECOLOGY OF WILD PIGS IN THE SOUTHEASTERN U.S.

SREL Collaborators: Jim Beasley, Sarah Chinn, Allie Rakowski

Population dynamics – how populations change in size and structure over time – is driven by factors such as vital rates (births, deaths), stochastic environmental variation, density dependence, and demographic variation (e.g., food availability, habitat quality, predation, immigration, emigration). Understanding drivers that influence population dynamics of wild animals are important for determining why and how populations increase, decrease, and fluctuate spatially and temporally under changing conditions. Reproduction, encompassing characteristics such as seasonality, age at maturation, fertility, energetic requirements, and the conditions that contribute to successful reproductive events, is a central component in the development of population models. We are conducting studies to better understand the reproductive ecology of wild pigs through direct counts of fetuses in pregnant sows, ovarian analyses, measurements of fetuses, and hormone analyses to ascertain conception date and make inferences about seasonal patterns of reproductive events (i.e., mating, farrowing). By sampling from various age classes (juvenile, yearling, subadult, adult), we may determine any differences in reproductive timing among age classes, as well as determine the age at sexual maturity for wild pigs.

EVALUATION OF METHODS USED TO ESTIMATE WILD PIG ABUNDANCE

SREL Collaborators: Jim Beasley, Gene Rhodes, Dave Keiter, Elizabeth Kierepka

Outside Collaborators: Kurt VerCauteren (USDA-APHIS), Kim Pepin (USDA-APHIS), Amy Davis (USDA-APHIS), Tim Smyser (USDA-APHIS), Toni Piaggio (USDA-APHIS), John Kilgo (USFS)

Currently, wild pig population sizes are most often estimated through the use of harvest indices, which are frequently biased. Improved methods of estimating abundance of this elusive species are necessary to aid researchers and managers in evaluating efficacy of control techniques, predicting potential impacts on ecosystems, and modeling disease risks. In collaboration with USDA-APHIS Wildlife Services and the US Forest Service, we are evaluating several methods of estimating population size of wild pigs. These include genetic capture-mark-recapture approaches, use of remote camera systems, an estimator based off of consumption of the biomarker Rhodamine B, and the creation of catch-per-unit-effort models from trapping of pigs. Our evaluation of the accuracy, cost-effectiveness, and robustness to violations of the assumptions involved in these methods will provide wildlife researchers and managers with a valuable toolkit for the future study of this invasive species.

MOVEMENT ECOLOGY OF TRANSLOCATED WILD PIGS

SREL Collaborators: Jim Beasley, Josh Smith, Lindsay Clontz, Allie Rakowski, Dave Keiter, Peter Schlichting

Outside Collaborators: Ryan Miller (APHIS-VS), Steven Sweeney (APHIS-VS)

Wild pig populations have been increasing in their introduced range as a result of intentional, and often illegal, translocation efforts by pig-hunting enthusiasts. These translocations are particularly harmful because of the ability of pigs to establish new populations in areas to which they are introduced. There has been practically no research, however, on the behavior of wild pigs following translocation. This is a critical data gap as the movement ecology of translocated wild pigs will have substantive implications for their ability to establish new populations and spread diseases to local wildlife, livestock, and humans. We are performing experimental translocations of GPS-collared pigs within the bounds of the Savannah River site to fill this data gap by investigating how the translocation process affects the spatial ecology and survival of wild pigs. This information will be used to model disease transmission risks and a number of other potential impacts of translocated pigs, informing management in areas where a translocation is suspected to have taken place recently, and provide insights into broader processes of invasion ecology.

MEASURING WILD PIG DAMAGE TO CORN AND PEANUTS

SREL Collaborators: Jim Beasley, Chris Boyce

Outside Collaborators: Kurt VerCauteren (USDA-APHIS), Steve Smith (USDA-APHIS), Noel Myers (USDA-APHIS)

Wild pigs are a substantial threat to agricultural production in South Carolina and Georgia. Though there is significant anecdotal evidence, little research has been done to measure the timing and extent of pig crop depredation. We are combining walked ground transects with unmanned aerial systems (UAS) multi-spectral imagery to identify and quantify damage to corn and peanut fields along the Congaree River near Columbia, SC and in Bamberg County, SC. With our data we hope to inform management practices to better time the control of pig populations in an effort to reduce the overall damage. There is also the potential of reducing the need for ground surveys if a suitable UAS-based approach is found. Additionally, we will be able to model location of damage relative to field edges and terrain features (roads, swamps, rivers). This information will provide landowners, farmers, and managers a better understanding of pig hot spots and locations to target.