By Jeff Burrell
[This is the third installment of a multi-part blog from the field at Trapper’s Point, Wyoming by WCS Scientists working to protect the Path of the Pronghorn.]Pronghorn (Antilocapra americana) are unique to the grasslands and sagebrush steppe of western North America — they are found nowhere else in the world. This pronghorn buck shows the characteristic pronged horns that gives this species its common name. Jeff Burrell ©WCS
For more than a decade, scientists from the Wildlife Conservation Society have conducted research and worked with partners to protect pronghorn migration to and from Grand Teton National Park along a more than 100-mile long migration corridor known as the Path of the Pronghorn. The animals migrate along this corridor between summer range in and around Grand Teton National Park and winter range in the Upper Green River Valley south of Trapper’s Point in western Wyoming. If this migration corridor is severed, pronghorn will be lost from Grand Teton National Park.
Pronghorn must overcome many obstacles during their migrations. Some, like steep cliffs and fast moving rivers, are found in nature. Others, including subdivisions, fences, and highways, are human-made. Trapper’s Point is at a natural bottleneck along the Path of the Pronghorn where the Green River and New Fork River pinch together. At this location, houses, fences, and US highway 191 further constrict an already narrow portion of the Path.
As traffic volume along US 191 has substantially increased, collisions between vehicles and pronghorn trying to cross the highway have likewise increased. As we reported in our first two blogs, the Wyoming Department of Transportation committed almost $10 million to construct fences, two overpasses and six underpasses to allow pronghorn, mule deer and other wildlife to move across the highway safely.
As part of WCS’s long term effort to protect the Path of the Pronghorn (the only federally-designated wildlife migration corridor in the United States) my colleagues Renee Seidler, Jon Beckmann, and I are combining data gathered from GPS collars worn by pronghorn with direct observations to assess how well the crossings are working. WCS research as well and photo-documentation work conducted by the group Western Ecosystems, Inc. will help us to improve these crossings and future wildlife crossing structures in other locations.
We set as our original goal to learn the answers to two questions: 1) Would construction activities disrupt pronghorn migrations; and 2) How well would pronghorn use the overpasses and underpasses? As we previously reported, while construction did sometimes cause confusion and stress for pronghorn, the migration was not disrupted. When pronghorn came to the new 8-foot high woven wire fence, they first tried to find a way under it. The fence worked as designed and blocked pronghorn from going onto the highway. Not finding a way under the fence, pronghorn sought another path, and the only path open to them was the new overpass. While pronghorn herds would sometimes take hours before using the overpass, they did all eventually use it to cross safely over US 191 as they continued their fall migration last year. Construction was completed in early October 2012.
We did also observe a few pronghorn reluctantly use one of the underpasses. This reluctance was as expected since pronghorn depend upon their incredible speed and equally incredible long-distance vision to keep them safe; going through a tunnel limits both. Mule deer on the other hand are comfortable going through underpasses and readily used both underpasses and the overpass.
We returned to Trapper’s Point for the spring 2013 migration. Some groups would move directly to and cross over the overpass, but others would again try their old route, be successfully blocked by the new fence, and only then find and use the overpass. Fortunately, all eventually did use the overpass.
This brings us to fall 2013. Would we see a repeat of the spring pattern or would pronghorn move directly to and use the overpass? We can now report the latter. Groups numbering from a few to more than 200 all directly moved to and used the overpass with little hesitation and little apparent stress or concern.
To sum up our findings to date, these highway crossings structures are a success. During the past year, these structures have allowed thousand of pronghorn and mule deer to cross US 191 – saving wildlife and preventing collisions. Credit for this success certainly goes to the Wyoming Department of Transportation for their decision to commit a sizable amount of funding for this work, and for contracting engineering firms for their outstanding wildlife overpass design and construction.
We’ll be back at Trapper’s Point for the spring 2014 migration to continue our study and assessment of the effectiveness of the crossing structures.
Jeff Burrell is the Northern Rockies Program Coordinator for the Wildlife Conservation Society. WCS efforts to protect the Path of the Pronghorn are supported by grants from the National Fish and Wildlife Foundation. For more information visit: http://www.youtube.com/watch?v=FjU44eVYJis