Looking Closer: How Wild Pigs Choose Farrowing Sites
By Tyjaha Steele
For many animals, where offspring are born can influence their survival from the very first few moments of life. Shelter, nearby resources, and protection from disturbance all play a role in reproductive success. For invasive wild pigs, understanding where females choose to give birth, known as farrowing sites, can provide insight into their reproductive behavior and help inform more effective management strategies.
To better understand how wild pigs select these nesting locations, researchers from the University of Georgia’s Savannah River Ecology Laboratory (SREL) and the Warnell School of Forestry and Natural Resources examined farrowing site selection at the Savannah River Site (SRS) in South Carolina. The work began as part of former graduate student Sarah Chinn’s, Ph.D. research, during which she led the field component of the study, and was later expanded upon by Travis Stoakley, a current SREL graduate student, who led the analysis and writing. The study focused on 24 mature female wild pigs monitored using GPS collars and internal transmitters that signaled when birth occurred.
“Within the southern U.S. wild pigs give birth throughout the entire year, with many sows giving birth twice in a given year,” explains Beasley, a researcher and professor from the University of Georgia’s Savannah River Ecology Laboratory (SREL) and Warnell School of Forestry and Natural Resources. “This incredible reproductive capacity is one of the contributing factors to their ability to rapidly invade new areas and one of the biggest challenges to controlling their populations.”
Wild pigs are among the most widespread and costly invasive mammals in the United States, causing billions of dollars in damage each year. Their high reproductive capacity allows populations to grow rapidly, making it difficult for land managers to slow or reverse their spread. While previous research has clarified when wild pigs reproduce, far less is known about the environmental features that influence where females choose to farrow.
Once researchers identified farrowing sites, they conducted detailed field surveys to document both fine-scale and broad-scale environmental characteristics. At each site, the team measured vegetation structure, light levels, temperature, canopy cover, and proximity to water. These features were then compared to nearby random locations to determine whether pigs were selecting specific conditions rather than using habitat at random.
The results suggest that female wild pigs consistently selected farrowing sites with dense and diverse understory vegetation and close access to water. All observed farrowing sites were located within a short distance of a water source, such as streams, ditches, or ephemeral pools. These areas may provide important thermal relief, hydration, and reduced travel demands during a time when females are less mobile and piglets are most vulnerable.
“Wild pigs are poor thermoregulators because they have few functional sweat glands, so they can’t easily cool themselves through evaporation and must rely on panting or behavioral modifications like seeking shade and water to cool down,” says Beasley. “Newborn piglets also have limited mobility their first few days, so having close access to water near the nest is likely important for both sow and piglet survival especially during hot summer months.”
Researchers found that fine-scale understory vegetation was a stronger indicator of farrowing site selection than broader forest type. Farrowing sites consistently occurred in areas with dense ground-level cover, even when the surrounding forest classification varied. When the team examined broader land cover patterns using satellite-based data, distance to water emerged as the only strong predictor of farrowing site selection, while other landscape features such as forest type or proximity to roads were used roughly in proportion to their availability across the study area. This finding highlights an important challenge for wildlife managers: features that matter most to reproducing wild pigs often occur at a scale too fine to be detected using commonly available land cover datasets.
“Sole reliance on remote sensing data can often lead to missing the important fine-scale cues that help us understand wildlife behaviors. Satellite data that generalize the dominant vegetation type of an area wouldn’t capture the diverse plant communities or understory vegetation composition in forested areas that are captured by boots-on-the-ground field surveys,” states Stoakley. “So while ecology research and wildlife management increasingly rely upon remote sensing technologies to inform our inferences, there is no substitute for good old-fashioned ground truthing.”
This study suggests that wild pigs do not rely on a single habitat type when selecting farrowing sites. Instead, females appear to prioritize areas that provide nearby water and dense understory cover, regardless of the surrounding forest type. This could help explain the species’ ability to thrive in a wide range of environments, and complicates efforts to control their populations.
By identifying the environmental features associated with farrowing sites, the research offers practical insight for wildlife managers working to detect and disrupt reproduction during key periods. Knowing where wild pigs are most likely to give birth can help guide targeted monitoring and removal efforts, particularly in areas where eradication or population reduction is a priority.
The full study, Multi-scale predictors of farrowing site selection of wild pigs (Sus scrofa), was published in Applied Animal Behaviour Science. Authors include Travis E. Stoakley, Sarah M. Chinn, David A. Keiter, Linda S. Lee, and James C. Beasley.
