The expansion of highways for traffic accommodation and safety improvements presents opportunities for improving wildlife connectivity (and reducing wildlife-vehicle collisions) by installing wildlife crossing structures and restoring adjacent habitats. The I-90 Snoqualmie Pass East Project was conceived to expand Interstate-90 in the Cascades Range of Washington State from 4 lanes to 6 lanes, improve highway safety, and reduce winter highway closures due to avalanches. Mitigation for expansion onto National Forest lands required the highway project to address ecological connectivity and reduce the barrier effect of the highway for wildlife and ecosystem processes. The project covers a 15-mile section of highway just east of the crest of the Cascade Range and incorporates > 20 major wildlife crossing structures. The project is unique in its scope and vision, working to improve ecological connectivity between the northern and southern Cascades across a broad array of taxa and ecosystem functions. Pre-construction monitoring began in 2008 and has expanded to include post-construction monitoring on the completed half of the project area. Washington State Department of Transportation (WSDOT) and others have monitored larger-bodied taxa (carnivores, ungulates), while Central Washington University research teams have focused on lower-mobility species including aquatic invertebrates, fish, amphibians, reptiles, and small mammals. Target species, locations, and methods varied with taxonomic group but were all conducted with a collective goal of identifying the local distribution, habitat use, population abundance, and population genetic structure of target species before and after construction. Connectivity was assessed by movement of marked individuals, colonization of crossing structures, detection by remote camera and genetic sampling. Early successes indicated by the movement of animals into crossing structures and across the highway were seen with cutthroat trout, coastal giant salamanders, shrews, deer mice, pikas, and larger-bodied mammals. We discuss the framework for decisions on monitoring, which involved meetings with the multiagency Wildlife Working Group. Challenges included multiple teams working independently on taxa requiring differing methods and spatial and temporal frequencies of monitoring; and study design for multiple structures that varied in type (over vs. under), dimensions, timing of installation, and adjacent habitat and landscape features. Early monitoring results have provided an opportunity for input into decision making by WSDOT on placement, design, and habitat features of upcoming crossing structures in the project, allowing adaptive management of the design and monitoring components of a comprehensive wildlife structure program.
Wildlife movement: connectivity, safety, across eco-tones
wildlife crossing structure