Ecological and genetic connectivity of shrews (Sorex spp.) across Interstate-90 in the Snoqualmie Pass East Project, Washington State.

Jordan Ryckman, Central Washington University
Kristina Ernest, PhD, Central Washington University, Ellensburg, WA, USA
Topic Area
Terrestrial Wildlife and Ecosystem Interactions with Transportation

Roads fragment habitat and disrupt the movement of wildlife. This decreases genetic variability and habitat availability for these populations. Interstate-90 (I-90) bisects Washington State in a vulnerable part of the Cascade Range near Snoqualmie Pass. The Washington State Department of Transportation (WSDOT) has created wildlife crossing structures, including overpasses, bridges, and culverts, to increase ecosystem connectivity. Small mammals are being monitored to evaluate their use and colonization of these structures as part of assessing how effective the structures are in improving connectivity for these low-mobility species. This project focuses specifically on shrews, which are often neglected in biological research due to their high mortality rate but regularly become bycatch of other monitoring projects. While largely insectivorous, they are opportunistic feeders, and may consume other small mammals. The main objectives of the proposed study are to determine the habitat preferences of the several shrew species that live near the crossing structures, and to assess the population genetic structure of the most abundant species. We will live-trap shrews on three pairs of grids north and south of I-90; each grid includes aquatic (in-stream), riparian, and upland habitat. Sherman traps, pitfall buckets, and funnel traps will be baited with mealworms to attract primarily insectivores (and reduce bycatch of rodents) and to provide sustenance for the shrews (thus reducing mortality). Polyester bedding will be placed in traps as insulation to reduce mortality rates. In the summer of 2019 a total of 1,440 trap-nights will be carried out with preliminary results expected in late August. We will also do ground-cover surveys to quantify microhabitat at each trap station. We will evaluate habitat and microhabitat preferences from the live-trapping data. We hypothesize that habitat preferences differ among shrew species, and that the riparian habitat supports more species and high abundances than the other habitats. We also hypothesis that microhabitats with high ground cover of leaf litter or herbaceous plants provide better foraging areas, and thus we predict higher shrew capture rates and more shrew species in these microhabitats. The results of the habitat analysis will be used to inform WSDOT of shrew habitat requirements for sites being restored within and adjacent to the crossing structures, and to provide microhabitat information for future restorations and the design of crossing structure features. In late fall 2019, we will examine genetic variability for the shrew species with the highest number of captures. Populations on the same side of the highway will be compared to populations on opposite sides of the highway to determine if I-90 has affected population genetic structure. This will provide baseline information for future evaluation of whether restoring the landscape with crossing structures and habitat has been successful.

Abstract Keywords
small mammals
genetic connectivity
habitat preference.