Pikas Rock! Use of linear infrastructure rock embankment and wildlife crossing structures by the American Pika (Ochotona princeps), a rocky habitat specialist

The American pika is a small mammal species in western North America that plays a key ecosystem role by consuming many plant species, creating food caches that other species may consume, adding nutrients via their latrines, and serving as prey for owls, hawks, weasels, and other predators. Pikas are habitat specialists, inhabiting patches of broken-rock habitat (e.g., talus slopes). Due to their patchy habitat and poor dispersal capacity, pikas have a classic metapopulation structure with limited dispersal between subpopulations (rock patches). Roadways that create barriers for dispersal make connectivity between subpopulations and metapopulations even more tenuous. Wildlife crossing structures with appropriate rock habitat have the potential to help restore connections within and among metapopulations. Here, I combine new and previously-reported data to provide a long-term context for how pikas respond to mitigation measures in a transportation project.
I conducted surveys for pikas in the I-90 Snoqualmie Pass East Project (SPEP) area of Washington State’s Cascade Range across multiple years to compare occupancy of natural and anthropogenic rocky sites and track colonization of new sites, including wildlife crossing structures. A subset of 10-15 of the potentially suitable rocky habitat sites in the 15 x 2 mile (24 x 3 km) study area was surveyed most years between 2009 and 2022. Occupancy surveys at each site consisted of 15-minute focal observations to watch for pikas and listen for their vocalizations, followed by walking transects across the site to search for haypiles and latrines (signs that pikas occupy the site). I summarized data by year, site, and site type to assess patterns of subpopulation dynamics (local extinction and colonization events, and time to colonization). Overall percent of sites occupied was high (80-90%) over the study area. Time to colonization of new rocky habitats varied from < 1 yr at one rock embankment site to > 8 yr at a site with anthropogenic rock piles. Pikas were detected at two of five wildlife crossing structures. As other studies have shown for larger species, long-term monitoring is also critical for assessing functionality of constructed habitat and wildlife crossing structures for smaller species with lower mobility. Due to limited dispersal and small body size, pikas may not colonize new or restored sites for several to many years. Time to colonization likely varies with distance from occupied patches and the matrix habitat through which pikas must disperse.
The methods and results of this study are relevant to other locations and other habitat specialist species, especially those with limited dispersal capacity. Long-term monitoring of wildlife crossing structures and constructed habitats along roadways and other linear infrastructure is critical for capturing variable colonization rates and for understanding population dynamics and success of connectivity enhancements.