The Effectiveness of Vertebrate Passage and Prevention Structures: a Study of Boeckman Road in Wilsonville

Wildlife collisions on roads are a serious issue resulting in property damage costs, injury to and possible death of the driver and passenger, and typically fatal results for the wildlife. Given the impacts to both drivers and wildlife, which may include at-risk or endangered animals, more recent attention has been given to modifying or retrofitting roads to facilitate wildlife passage. There has not been sufficient research done to determine the actual utilization of various wildlife passage structures. In the city of Wilsonville, Oregon, the Boeckman Road Extension project will be concluding construction in spring 2008. This road provides a unique…

Wildlife collisions on roads are a serious issue resulting in property damage costs, injury to and possible death of the driver and passenger, and typically fatal results for the wildlife. Given the impacts to both drivers and wildlife, which may include at-risk or endangered animals, more recent attention has been given to modifying or retrofitting roads to facilitate wildlife passage. There has not been sufficient research done to determine the actual utilization of various wildlife passage structures.

In the city of Wilsonville, Oregon, the Boeckman Road Extension project will be concluding construction in spring 2008. This road provides a unique opportunity to examine the efficacy of multiple types of passage and prevention structures in a given area where no road existed previously. Wildlife passage was taken into great consideration in the construction of this road and as a result it includes a bridge, two large box culverts, and eleven small round culverts to facilitate wildlife passage. In addition, the road will be lined in key places with an amphibian wall and deer fence to prevent wildlife from getting onto the road. Both of the large culverts and three of the small culverts include elements that will allow natural light to penetrate the culvert. A mammal wildlife survey conducted at the Boeckman road site prior to construction found evidence of black tailed deer, raccoon, coyote, nutria, beaver, mink and river otter. Adjacent lands are considered prime red legged frog habitat and the presence of a pond as well as an upland island could someday provide essential western pond turtle habitat.

Using motion detection cameras and tracking methods coupled with road kill surveys, the types, frequency, and preferences of animal (mammal, amphibian and reptile) passage will be determined. We will also use cameras to monitor locations at transects parallel and perpendicular to the road. These transects will provide general information on movement and species of animals utilizing this location and will provide a comparison to usage rates of the passage structures. Pit traps will be used at strategic locations along the amphibian/reptile wall to verify its use and effectiveness and to determine species present. We will also manipulate light levels in the large and small culverts to determine the role of natural and artificial light on diurnal and nocturnal usage.

Determining the species-specific use of the different passage types and the efficacy of fencing will help identify best environmental practices for future projects and retrofits. This information should help match structure type to species of most concern, improving animal use and avoiding costs of less effective passages and fencing. The results of this study will also provide information valuable to assessing the proper passage structures in sensitive habitats, aiding transportation planners and wildlife biologists in working together to make the best assessment for the given area. The proposed project will be an important first step in a broader study that will include comparisons of other roadways, with and without culverts and fencing, and additional types of passage structures.