Connecting the Dots: Behavioral State Resource Selection in Wild Pigs in the Southeast United States

Abstract

Background Invasive wild pigs (Sus scrofa) are behavioral generalists that have the potential to alter ecosystems across broad spatial scales. Elucidating the correlation between wild pig behavior and landscape attributes can aid in the advancement of management strategies for controlling populations. Methods Using GPS data from 49 wild pigs in the southeastern U.S., we used movement characteristics to distinguish and define behaviors and explore the connection between these behaviors and resource selection for both females and males between two distinct seasons based on forage availability. We extracted three biologically relevant behaviors of wild pigs from our movement data using hidden Markov models, which we inferred to represent resting, foraging, and traveling behavioral states. We then used multi-scale resource selection functions to quantify resource selection at the population and home-range scales for each behavioral state. Results Females demonstrated a crepuscular movement pattern in the high-forage season and a variable pattern in the low-forage season, with increased traveling and foraging activity during the daytime and evening hours, while males consistently demonstrated a nocturnal pattern across both seasons. At the population scale, wild pigs selected for forest vegetation types (i.e., upland pines, upland hardwoods, bottomland hardwoods) in both the low- and high-forage seasons, likely reflecting their ubiquitous establishment throughout the landscape. At the home-range scale, wild pigs selected for bottomland hardwoods and dense canopy cover in all behavioral states. In addition, males demonstrated selection for a variety of vegetation types while foraging in the low-forage season compared to the high-forage season and demonstrated an increased use of linear anthropogenic features (e.g., roads) across seasons while traveling. Conclusions Our results demonstrate male and female pigs exhibit clear differences in movement behavior. Further, although wild pigs can establish populations and home ranges in an array of landscapes and habitat types, there are key resources associated with common behaviors they select consistently at a fine scale that can be targeted in conservation and management programs across their invasive range.

Habitat quality influences trade-offs in animal movement along the exploration-exploitation continuum

“…Approximately 68% of habitat on the SRS consists of upland pine forest containing interspersed riparian areas, with another 22% comprised of bottomland hardwood forest, and the remaining areas consisting of open water, shrublands, industrial areas, and grasslands 34 . Although wild pigs occur throughout both upland pine and bottomland hardwood habitats on the SRS 35 , movements are often concentrated within bottomland hardwood and other riparian habitats 31,36 . Upland pine forests on the SRS are dominated by loblolly pine (Pinus taeda), long-leaf pine (P. palustris), and slash pine (P. elliotii) and are managed by the USDA Forest Service for timber and wildlife habitat 34 .…”

“…To quantify resource selection, we used data from the National Land Cover Database (https://www.mrlc.gov/data) with a resolution of 30 X 30 m. We condensed the 17 habitat classi cations to three coarse land cover types: bottomland (e.g., marsh, wetlands, bottomland hardwood), upland pine (e.g. pine woodlands), and shrub/grassland which we assumed differed in provision of food and cover for wild pigs 29,31,42 . To assess selection of these habitat types we used Step Selection Functions (SSFs) 43 .…”

“…We ranked all models using Akaike Information Criterion (AIC) 46 . Additionally, we performed a post-hoc test to assess whether resource selection differed between diel periods 31 . We added an interaction term indicating whether the location was taken during diurnal or nocturnal time periods to our top-ranked model above.…”

“…Our second objective was to determine how selection for our hypothesized preferred habitat type (bottomland) differed through time based on release habitat type, and between resident and translocated individuals (Table 1B). For this analysis we estimated weekly selection coe cients for bottomland habitat for each group based only on nocturnal locations 31 .…”

“…Although generalist foragers, wild pigs are heavily dependent on wetland and riparian habitats for foraging, resting, and thermoregulation [29][30][31] . Thus, riparian areas and bottomland hardwood swamps are considered high quality habitats for wild pigs, particularly relative to pine-dominated forests, and the distribution of these preferred habitats has a strong in uence on wild pig movements 32 .…”