Testing the forage preference of the American pika (Ochotona princeps) for use in connectivity corridors in the Washington Cascades

One of the aims of the Snoqualmie Pass East Project (SPEP) in the Cascades of central Washington is to construct nearly 30 wildlife crossing structures along a 15-mile stretch of Interstate-90. American Pikas (Ochotona princeps) are being monitored for the SPEP because they have specific habitat requirements and are poor dispersers. Making the crossing structures “pika-friendly” will encourage these low-mobility animals to use the structures. Recent research suggests that the presence of quality vegetation may help pika populations avoid declines and extirpations, so planting suitable forage within and adjacent to the crossings will be essential. During the summer and fall of 2015, we completed 70 cafeteria-style preference experiments using 10 forage species that were common in pika-occupied habitats. In these trials, pikas were given equal forging access to 5-6 species at the same time. The results of these trials were analyzed using the Jacobs’ Selectivity Index, Hotelling’s T tests, and one-sample t-tests. Douglas fir (Pseudotsuga menziesii), Sitka alder (Alnus viridis), willow (Salix spp.), and black cottonwood (Populus balsamifera trichocarpa) were the most selected species, and were recommended for planting in the upcoming crossing structures. Samples of each of the tested plant species were also analyzed for nutritional components and some plant secondary metabolites. Linear regression was used to evaluate which plant components influenced pika forage preference. Pikas selected for plants that contained either 23 alkaloids or high levels of tannins. However, when both alkaloids and high levels of tannins occurred within the same plant, forage preference declined. Introduction As human populations grow at an almost exponential rate, more roads are constructed and widened to accommodate increased travel and development in new areas. The fragmentation of natural habitats by roads can have many effects on ecosystems, including reduced amount and quality of available habitat, restricted access to resources and migration routes, increased mortality from animal-vehicle collisions, and segregated populations that may experience declining genetic diversity (Beckmann et al., 2010). One strategy that can help ameliorate several ecological impacts of roadways is the construction of wildlife crossing structures such as wildlife bridges, underpasses and expanded culverts. These structures are already popular in Canada and parts of Northern Europe and Australia, and are starting to be used in the United States. Underand overcrossings that are already in operation around North America have reduced the number of animal-vehicle collisions for some species and have also aided in reconnecting wildlife populations (Foster and Humphrey, 1995; Huijser et al., 2007). As aging highways across the country require major repairs and lane expansions, opportunities arise to include crossing structures within the construction plans (Forman et al., 2003). In the Cascade Mountain Range (the Cascades) of central Washington State, one such project is taking place on Interstate-90 (I-90), a divided, 4 to 6-lane federal interstate highway. The Snoqualmie Pass East Project (SPEP) is currently making several improvements to I-90 that will repair failing infrastructure, ease congestion, and enhance 24 human safety. The project is also constructing nearly 30 different fish and wildlife crossing structures throughout a 24-km stretch of highway (Long et al., 2012). These crossings will include widened, bottomless culverts for improved continuity within aquatic habitats, and also several small and large overand under-crossings that will help reconnect terrestrial wildlife populations. The crossing structures will be planted with native vegetation, including trees, and will contain rock piles, downed logs, and other features necessary to help imitate the surrounding natural habitat. Most previous connectivity projects in the North America have focused on the movements of high-mobility animals, usually ungulates and mammalian carnivores (Cain et al., 2003; Forman et al., 2003). The crossings for the SPEP, however, are also making considerations for a variety of small native species, including small mammals, reptiles, amphibians, fish, and invertebrates, that are often over-looked in crossing projects. The SPEP is also focused on ecological processes because the overall goal of the project is to attempt to reconnect every part of the local ecosystem, not just populations of large mammal species (WSDOT, 2006). One small mammal that is being monitored with respect to the SPEP is the American pika (Ochotona princeps). Pikas are small, generalist herbivores of the order Lagomorpha (rabbits and hares) that inhabit rocky talus slopes, usually in mountainous areas. These talus slopes are often dispersed across mountainsides in discrete patches (Krear, 1965). Pikas rely on the talus for thermoregulation and for protection from predators, so they rarely stray more than a few meters from the edge of the talus even to