ACCEPTANCE OF WILDLIFE CROSSING STRUCTURES ON US HIGHWAY 93 MISSOULA,MONTANA

Jeremiah P. Purdum, The University of Montana

Abstract

Wildlife and humans have always interacted on the landscape. However, growing transportation infrastructure and its associated use are causing a large increase in direct and indirect effects on wildlife populations. Humans can also directly be affected, for example, through wildlife-vehicle collisions that impact human safety and lead to economic costs for individuals and society. In some cases transportation and wildlife agencies have implemented substantial mitigation measures along roadways in an attempt to reduce wildlife-vehicle collisions and to provide for safe crossing opportunities for wildlife. Wildlife-specific crossing structures are now increasingly considered in road construction. Reconstruction projects and a range of studies have reported on the effect of structural attributes on wildlife use to help guide crossing structure design and improved effectiveness. However, measuring wildlife use of structures does not account for the effect of varying population sizes or the willingness of wildlife to come close to the highways and the crossing structures. Passage success (number of successful passage attempts/number of total approach events) may be a more biologically meaningful measure of crossing structure effectiveness. I investigated the acceptance of wildlife crossing structures by wildlife species using 17 wildlife crossing structures associated with US Highway 93 on the Flathead Indian Reservation north of Missoula, Montana. Overall acceptance was high among most species including 80% or higher for black bear (Ursus americanus), bobcat (Lynx rufus), coyote (Canis latrans), and white-tailed deer (Odocoileus virginianus) while mule deer (Odocoileus hemionus) exhibited a lower acceptance rate of 67%. I used logistic regression to predict the probability of acceptance given the immediate structural attributes of the crossing structures. Species showed varying relations to crossing structure attributes. White-tailed deer acceptance was most positively associated with the height of a structure. Mule deer acceptance of crossing structures was associated with their ability to see past the exit of a crossing structure and the absence of a water channel in a structure. Acceptance by a group of carnivores (black bear, coyote, and bobcat combined) showed a positive association with the height of a structure as well as the ability to see past the exit of the crossing structure. I recommend that decision makers use acceptance of structures as a parameter rather than use alone when choosing the appropriate type and dimensions of crossing structures given certain target species.