Document Type


Date of Degree Completion

Spring 2018

Degree Name

Master of Science (MS)



Committee Chair

Kristina A. Ernest

Second Committee Member

Paul W. James

Third Committee Member

Daniel D. Beck


Expanding transportation corridors have fragmented ecosystems throughout the world, restricting the movement of organisms or acting as complete connectivity barriers. Wildlife crossing structures (WCS) can increase the permeability of roads, allowing animals to move safely between habitats. Small mammals are especially vulnerable to the effects of reduced connectivity because of their limited mobility; however, few studies have evaluated their use of WCS. This study was conducted at a WCS under I-90 near Snoqualmie Pass, Washington. Our objective was to evaluate the small mammal species composition at the wildlife undercrossing in comparison to adjacent restoration sites and to the nearby forest. Additionally, we sought to evaluate small mammal preference for installed habitat features at all sites. We used live trapping, track tubes, and wildlife cameras to assess number of species, relative abundance, and habitat use. Our results indicated fewer species, and a greater abundance of generalist species, near the crossing structure than in the nearby forest. Small mammals showed no preference for any particular habitat features (rock piles, brush piles, fallen logs, or open) within the trapping grids, but were more likely to be captured near any feature than in open areas. Two years post-construction, the WCS contained a small subset of the species in the nearby forest. We expect the number of small mammal species using the crossing structure to increase in the future as the habitat develops and creates an environment more supportive of rich biodiversity.