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

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

The Suitability Of Large Culverts As Crossing Structures For Deer

Most researchers that have investigated the use of wildlife crossing structures have done so through counting the number of animals present in the structures or the number of animals that crossed the road using the structures. However, we argue that crossing structure acceptance, as a percentage of all approaches, is a better measure of suitability. Once the acceptance of certain types and dimensions of crossing structures is known for different wildlife species, agencies can select crossing structures that meet certain goals. We used this method for one particular type of crossing structure; large diameter culverts. We placed wildlife cameras (Reconyx™) at the entrance of nine corrugated metal arched culverts located along US Highway 93 on the Flathead Indian Reservation, Montana; to capture approach behavior. We specifically examined the number of successful and aborted crossing attempts. White-tailed and mule deer were the most frequently observed species and had an acceptance rate of 84 percent (n = 455) and 66 percent (n = 56) respectively. Only 49 percent (n = 426) of the groups that passed the structures successfully showed an alert posture versus 93 percent (n = 98) for the groups that aborted the attempts. The two deer species showed slightly different levels of alertness with an alert posture for 55 percent of white-tailed deer (Odocoileus virginianus) events and 68 percent for mule deer (O. hemionus)events for all crossing attempts combined. The data show that wildlife acceptance rates and behavior at structures can vary between species and data on varying structure type and dimensions will add to our understanding of structure acceptability for various target species