Mule deer use of underpasses in Western and Southeastern Wyoming

Underpasses have been found to be a valuable mitigation tool in increasing permeability of roads to wildlife while preventing roadside mortality. Underpasses are currently used in Wyoming on Interstate 80 near Arlington and Walcott Junction in conjunction with 2.4meter-high fencing to allow mule deer to pass under two stretches of road that bisect migration routes of mule deer. One experimental underpass has been installed in Nugget Canyon on U.S. Highway 30 between Kemmerer and Cokeville in western Wyoming to assess the effectiveness of underpasses in mitigating deer-vehicle collisions along a 15-mile stretch of highway that bisects the migration route of a subunit of the Wyoming Range mule deer herd consisting of 14,000 animals. A monitoring study using 35mm cameras activated by Trailmaster TM1500 infrared sensors was initiated in fall of 2001 to assess mule deer use of six underpasses on Interstate 80. Results from this study were used to inform a project examining the response of mule deer to manipulations of the openness ratio of the Nugget Canyon underpass which entailed video monitoring of the underpass to gather data on deer behavior. We found that of the six underpasses we monitored along Interstate 80, only one was consistently used by mule deer. This underpass had a high openness ratio and was located near a historic mule deer migration route. At the Nugget Canyon underpass, we found that percentage of mule deer repelling from the underpass was significantly correlated with underpass openness. Mule deer responded more to alterations in underpass width than height. Based on our results, we recommend that future underpasses constructed in Nugget Canyon be at least 20 feet wide and 8 feet tall and have an openness ratio of at least 0.8