Identifying Road Segments that Bisect Predicted Movement Corridors for Small Priority Species in Virginia

About the report

The Virginia General Assembly passed legislation in 2020 requiring the preparation of the Virginia Wildlife Corridor Action Plan. It directed the Virginia Department of Wildlife Resources in collaboration with the Virginia Department of Transportation, the Virginia Department of Conservation and Recreation, and the Virginia Department of Forestry to identify wildlife corridors, identify areas with a high risk of wildlife-vehicle collisions, and recommend wildlife crossing projects intended to promote driver safety and wildlife connectivity. The first version of the Wildlife Corridor Action Plan was released in 2023 and listed several “recommendations for future actions” for its next iteration. Four of these future actions include (1) identifying at-risk terrestrial species, aquatic species, and other species of interest whose corridor needs are not sufficiently addressed by the Wildlife Biodiversity Resilience Corridors; (2) identifying important habitat corridors for these species; (3) identifying Wildlife Crossing Concern Areas (e.g., high-risk road segments) for these at-risk species; and (4) identifying and analyzing non-road human barriers (e.g., land uses) affecting corridor connectivity for the Wildlife Biodiversity Resilience Corridors.

The purpose of this study was to advance the objectives of the legislated Wildlife Corridor Action Plan by developing species-specific road risk models and identifying road segments that pose a high risk to small priority species. To identify high-risk road segments, the authors collaborated with 29 species experts to develop maps of “landscape resistance” for 12 state species on the Species of Greatest Conservation Need list. These maps represent how different landscape features are expected to affect species movement—by increasing mortality risk, influencing movement speed, acting as physical barriers, or causing behavioral avoidance. Species-specific connectivity analyses were used to generate maps of predicted movement intensity for each species and to identify areas where roads were expected to cause the greatest reductions in movement.

The 12 priority species considered in this analysis varied widely in distribution, resulting in large differences in the spatial extent and configuration of predicted movement corridors. The Mabee’s salamander was unique in having compact movement zones predicted around a small number of extant source populations. For this species, a focused set of priority road segments was identified that may be suitable for site-level assessment and mitigation—such as improving existing culvert passability or adding targeted small-animal passages. Several species, including the bog turtle, wood turtle, diamondback terrapin, mud snake, rainbow snake, and fisher, had much broader but regionally concentrated movement corridors that intersected a modest number of important roads. The prioritization of road segments for these species reflects both proximity to key source habitats and road characteristics associated with high resistance to movement (e.g., high traffic volume and greater road width). For several wide-ranging species (spotted skunk, Alleghany woodrat, spotted turtle, and box turtle), predicted corridors were diffuse and covered large portions of the state. Mitigation efforts for such species should likely focus on roadway design standards (e.g., use of fencing or curbing to funnel animals to existing structures and ensuring underpasses are compatible with small-animal use) rather than prioritizing individual crossing sites. This project provides connectivity map outputs for all 12 priority species as geographic information system raster data. It develops a consistent, repeatable workflow for assessing road impacts and connectivity across multiple taxa in Virginia.

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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