Wildlife crossing mitigation on a rural Colorado state highway

Abstract

Colorado’s Western Slope is home to several of the largest herds of migratory mule deer (Odocoileus hemionus) and elk (Cervus elaphus) in North America. Highways bisect important ranges and migratory corridors, creating significant conflicts between wildlife and vehicles. As a result, the state documents reported 4,000 wildlife-vehicle collisions each year, costing an estimated $66.4 million annually in damages. Research suggests that wildlife crossing structures can reduce ungulate-related wildlife-vehicle collisions by 80-90%. Appropriately sized wildlife crossing structures, combined with exclusionary fencing to guide animals to the structures, are the most effective mitigation options for reducing wildlife-vehicle collisions and restoring or maintaining habitat connectivity. Therefore, my study evaluated the effectiveness of phase I of a wildlife mitigation project constructed along a rural highway in northwestern Colorado. Wildlife use of the crossing structures was monitored using motion-triggered cameras for two-years post-construction to document species presence, movement behavior, and successful passage events. I also analyzed carcass and crash data to determine whether the mitigation successfully reduced wildlife-vehicle collisions within the mitigated area. Post-construction monitoring showed that mule deer were the most frequently detected species and used all crossing structures. Elk used the large underpass more consistently than the small underpass structure. Other species, including black bear, bobcat, coyote, mountain lion, moose and smaller mammals were also detected, indicating use from a diverse array of wildlife. In addition, carcass and collision data suggested an 86 to 97% decline in wildlife-vehicle collisions within the mitigated area post-construction. Overall, the first two years post-construction indicated a reduction in reported crashes and a diversity of species approaching and using the crossing structures. Monitoring will continue for three additional years to determine continued successful passages and movement behaviors within the mitigated area.