Evaluation of Underpass Installed US Highway 30 at Nugget Canyon, Wyo. for Migrating Mule Deer: FWA-WY-03/01F
A 15-mile stretch of U.S. Highway 30 through Nugget Canyon between Kemmerer and Cokeville, Wyo. bisects the migration route of a subunit of the Wyoming Range mule deer herd. Consequently this highway is crossed by approximately 14,000 mule deer each fall and spring as they migrate between their winter range in Red Eye Basin and their summer range in the Wyoming Mountains.
An average of 130 mule deer per year have been killed in deer- vehicle collisions since 1990. An underpass was installed in association with 8-foot-high deer-proof fence at milepost 30.5 in the summer of 2001 in an attempt to mitigate this problem.
Starting in the fall of 2001 the Wyoming Department of Transportation (WYDOT) funded the Wyoming Cooperative Fish and Wildlife Research Unit (WCFWRU) to conduct a study to evaluate mule deer activity at the underpass and to determine the optimal size and potential locations of future underpasses to be built in Nugget Canyon.
We monitored the underpass using a videocamera system activated by infrared sensors to examine deer activity at the underpass. Starting in the spring of 2002, we initiated a series of trials in which we manipulated the size of the underpass using plywood dividers and gauged mule deer response to the underpass at different sizes. We collected data on the number of deer entering the underpass, the number of deer repelling from the underpass, the time needed for deer to enter the underpass, and behavioral indicators of hesitancy as deer approached the underpass. We also collected tracking data and analyzed mortality data provided by the Wyoming Game and Fish Department (WGFD) to assess deer activity in other locations between mileposts 27 – 42 in Nugget Canyon.
Based on video footage of the 2000-2003 migrations and herd estimates provided by WGFD, we found that between 8.4 percent and 11 percent of the mule deer crossing the highway in Nugget Canyon used the underpass at milepost 30.5. In the years the underpass was monitored the peak of fall migration occurred in December and the peak of spring migration occurred in March and April.
We found that deer approaching the underpass were more likely to repel in response to smaller underpass sizes than larger. Deer were more sensitive to changes in the width of the underpass than the height. Height reductions down to 8 feet did not appear to substantially impact deer willingness to use the underpass, but reductions to 6 feet resulted in a large increase in percentage of deer repelling from the underpass. Deer crossing traffic on U.S. Highway 30 was heaviest at mileposts 35 and 36, at the east end of the deer proof fence.
We recommend that future underpasses built in Nugget Canyon be at least 20 feet wide and 8 feet tall, and have an openness ratio of at least 0.8. At least one additional underpass should be built in Nugget Canyon near mileposts 35 and 36, and the deer-proof fence extended at least 3 miles east of its current extent to prevent deer from moving around the end of the fence.