Road Ecology Center

Small mammal populations separated by highways may be partially or completely isolated from one another due to low dispersal capabilities, low probability of surviving highway crossing attempts, and/or avoidance of areas adjacent to highways. Threats to small mammals are problematic at the ecosystem level because of their importance as seed dispersers and their role as prey for predators, such as marten, wolverine, and raptors. Our objective is to determine how movement and gene flow are affected by two- and four-lane highways for small mammals in forested areas of western Montana. We trapped small mammals at five highways sites for two summers using a mark-recapture protocol. We gave each animal an individual mark so that we could follow their movements through time and collected either hair or a small tissue sample for genetic analyses. We are assessing potential fragmentation of small mammals populations by comparing movement rates and gene flow adjacent to the highway versus across the highway. Our preliminary results suggest that highways inhibit movement of small mammals. Movement was hindered more by four-lane than by two-lane highways. We observed stronger effects on red-backed voles and chipmunks, and weaker effects on deer mice. Deer mice were responsible for the vast majority of highway crossings, while only one vole and no chipmunks crossed four-lane highways. Through ongoing genetic and markrecapture analyses, we hope to determine whether or not this poses a biologically significant problem for forest small mammals.