Seasonal and Temporal Influences on Successful Crossing Rates by Ungulates of a North Utah Wildlife Overpass

Encroachment of human infrastructure fragments wild landscapes and introduces a suite of negative impacts for humans and wildlife. In Utah, roadways threaten migratory ungulates by creating a barrier to movements and preventing access to seasonal migration routes. To mitigate these conflicts, state transportation agencies often install wildlife crossing structures to allow animals to safely cross over or under roadways. Selecting the proper crossing structure requires consideration of the species of interest, landscape, location, and structural dimensions. Often there is balance between the optimal location, the dimensions of the crossing structures, and what is feasible given the landscape. In 2018, the Utah Department of Transportation installed an overpass that was much longer than it is wide (0.13 width to length ratio, the recommended ratio is 0.8) across a major Interstate. The purpose of my study was to determine if the target species, mule deer (Odocoileus hemionus) as well as other animals such as moose (Alces alces) and elk (Cervus canadensis) would use this crossing structure. Additionally, I sought to determine if there were seasonal or temporal influences on successful crossing rates. I conducted an observational study using trail cameras installed along Parley's Canyon Overpass from April 2020-July 2022, to record wildlife use of the overpass. I evaluated the proportion of crossings for mule deer, elk, and moose that occurred during different times of the day and among seasons. Mule deer and moose successfully used the overpass 97.9% (of 1,973 visits) and 100% (of 65 visits) of total visits; however, elk only made 3 successful crossings (23.08%). I determined that, due to high success rates regardless of season or time of day, mule deer feel safe enough to cross this overpass if they encounter it regardless of timing of when they encounter it. Additionally, overpasses with smaller width to length ratios like this one can be used by mule deer and moose successfully, but not elk. My research will add to the literature regarding issues in transportation, wildlife ecology, and wildlife behavior that aid in determining wildlife crossing structure design and placement preferences by ungulates in the American west.