Reducing Wildlife Mortality on Roads in Vermont: Documenting Wildlife Movement near Bridges and Culverts to Improve Related Conservation Investments
Paul Marangelo & Laura Farrell - 2016
Organization: Vermont Agency of transportation
This project gathered and analyzed game-camera data on the frequency of under-highway wildlife movement through bridges and culverts in Vermont. Our analytical objective was to generate results-based recommendations for improving the permeability of highways in Vermont to increase the frequency of under-road movement of wide-raging terrestrial species. Specifically, this project assessed and then modified an analytical framework developed in the western United States that characterizes 1) the usability of a given structure for wildlife through-passage; and 2) relationships between species use and transportation structure size for applicability in Vermont. 573 through-passages of a set of 13 focal species were recorded at 23 culverts and bridges on busy road corridors. Results indicate that a modified framework that relates potential species use to culvert/bridge size is useful for identifying the potential benefit of projects to increase transportation structure usability for wildlife, provided that a given structure and habitat in its vicinity are suitable for wildlife. Variation in through-passage data among sites suggested the importance of site and structural characteristics in determining the frequency of use of a given bridge or culvert, specifically identifying local-scale structural connectivity, the presence of nearby deterring factors such as pens of hunting dogs, and the availability of dry even movement surfaces inside of a structure as important. Also, we estimate that only a small minority of transportation structures on the highway system in Vermont are currently usable by wider-ranging wildlife, and that existing culverts and bridges ill-serve the needs for cross-road wildlife movement in Vermont. While there is a need to refine our understanding of the influence of structure design characteristics on wildlife through-passage, the modified framework that relates structure size and species use and insights about the apparent influence of some site characteristics on wildlife use will likely prove useful for informing future projects aimed at increasing the permeability of highways in Vermont for wildlife.
Document Type: pre-mitigation monitoring guidelines