Wildlife underpass use with gaps in exclusion fences along a 4‐lane highway 15 years post‐construction

Abstract In 2005, 3 wildlife underpasses were installed on a section of U.S. Highway 64 in Washington County, North Carolina, USA, with a 3 m tall, chain link exclusion fence passing under the road and extending ≥ 800 m from each underpass in both directions and parallel to the highway. Over time, the fencing developed gaps, potentially reducing the efficacy of the underpasses. From 2019 to 2021 we monitored wildlife activity using passive infrared cameras at the underpasses and 15 gaps in the fencing. Our goals were to determine differences in species’ use of the fence gaps vs. underpasses and what factors influence wildlife gap‐use behaviors. Wildlife gap‐use behaviors were species‐specific. White‐tailed deer ( Odocoileus virginianus ), northern raccoons ( Procyon lotor ), bobcats ( Lynx rufus ), and black bears ( Ursus americanus) had >50% of their observed events using the underpasses, while canids, aquatic mammals, rabbits ( Sylvilagus floridanus and S. palustris ), and Virginia opossum ( Didelphis virginiana ) were detected >50% of their events using the gaps. All species/taxonomic groups were observed using the gaps in the fencing. When detected below the underpasses, all taxonomic groups except aquatic mammals were observed on the outside, or roadside, side of the fence. We regressed species, season, year, gap size, gap distance from underpass, and frequency a species was walking parallel to the fence to the proportion of events a species was observed on the roadside of the fence with the highway. Our regression model ( F 9 , 947 = 16.23, P < 0.001) indicated that groups used the gaps at different rates. We observed approximately a 19% decrease in gap use between 2019 and 2021. Additionally, the percentage of events where animals were observed walking parallel to the fence on the safe side—without passing through the gap—was positively correlated with gap use at 0.03. Animals tended to use gaps associated with underpasses that had wider horizontal clearances as opposed to gaps near underpasses with narrower horizontal clearances. Similarly, animals used gaps that had taller vertical clearances more than gaps with shorter vertical clearances. Wildlife exclusion fence maintenance is often neglected, and post‐construction studies generally focus on crossing structures. When fencing is left unattended, gaps can develop, creating the potential for more wildlife‐vehicle collisions. Our study highlights the importance of long‐term monitoring and maintenance of wildlife crossings and fencing designs, emphasizing their implications for effective and safe animal movement.