Multi-scale predictors of farrowing site selection of wild pigs (Sus scrofa)

Abstract

The ability to monitor and anticipate reproductive activity is essential to effectively control invasive wildlife species, especially for globally-distributed vertebrates like wild pigs (Sus scrofa) that incur immense management costs each year. While recent studies have made substantial progress in clarifying the temporal dynamics of wild pig reproductive ecology, several aspects of the spatial dynamics of wild pig reproductive ecology warrant additional attention. Specifically, the factors that influence selection of nesting sites (called farrowing sites for wild pigs) are understudied. While previous studies have characterized nest dimensions, composition, and associated plant species, the multi-scale vegetation community composition and environmental predictors of farrowing site selection are relatively uncharacterized. To better understand the spatial component of wild pig farrowing site resource selection, we assessed the fine- and broad-scale land cover and environmental predictors of farrowing sites for 24 mature female wild pigs at the Savannah River Site in South Carolina, USA, between May 2016 – February 2020. Wild pigs monitored in our study established farrowing sites in areas with diverse understory vegetation and were always near water. Compared to farrowing sites used in autumn-winter, sites used in spring-summer had greater light intensity but not greater canopy cover. Nests were predominantly located in upland pine stands or hardwood-dominated riparian areas, and selection was generally proportional to the land cover composition of the study area. Distance to water was the only statistically predictive broad-scale land cover covariate of farrowing site selection in our study. Fine-scale vegetation analyses outperformed broad-scale analyses for predicting farrowing site selection, which inherently hinder managers’ ability to use publicly-available satellite imagery to readily identify areas where parturition is most likely to occur. Therefore, knowledge of fine-scale vegetation composition of an area can improve managers’ ability to discover active or recently used farrowing sites—signals of reproductive activity that are essential for managers to monitor during intensive management or eradication programs. Overall, understanding the spatial patterns of reproduction is important for managing and eradicating target invasive species, and the ability to monitor and anticipate where reproduction occurs around peak reproductive periods can guide management efforts.