Literature Review Highway Wildlife Mitigation for Wisconsin, USA

Abstract

This literature review relates to the effectiveness of mitigation measures along highways in Wisconsin that are aimed at: 1. Improving human safety through reducing collisions with common large wild mammal species and species that are of conservation concern, and 2. Reducing the barrier effect of roads and traffic for common large wild mammal species and for species that are of conservation concern. We summarized the effectiveness of measures aimed at influencing driver behavior, influencing animal behavior or population size, and measures that aim to physically separate animals from roads and vehicles We also distinguished between measures that are targeted at large wild mammals versus small animal species including amphibians, reptiles, and small mammals. If the objectives include both reducing collisions with large wild mammals and maintaining or improving connectivity for large wild mammals, and if ethics regarding associated impacts are considered, then there is only one approach that is highly effective: wildlife barriers (fences) in combination with wildlife crossing structures (underpasses and overpasses). For small animal species, fences in combination with wildlife crossing structures are similarly effective. However, temporary or permanent road closure and road removal are also sometimes implemented for small animal species. Since these measures limit the routes people can drive, these measures are usually very local and they mostly relate to short road sections that have, or had, very low traffic volume. Local measures are unlikely to benefit large mammal species that have large home ranges and that have populations that tend to occur over large areas. But small animal species may have very specialized habitat (e.g. a wetland) and small home ranges. Therefore, the small spatial scale of temporary or permanent road closure and road removal can be meaningful to small animal species. Nonetheless, the barrier effect of a road with open habitat and a non-natural substrate remains with temporary or permanent road closure. Only when road removal is combined with habitat restoration can the barrier effect disappear. Assisted road crossings for small animal species are somewhat comparable to wildlife crossing personnel for large mammals. This can reduce direct road mortality, but the barrier effect may or may not be addressed.