Roads are barriers to ecosystem connectivity, harming wildlife populations. Some animals live in modified habitats along roads, but their fitness in these stressful environments is poorly understood. Chronic stress alters behavior, and reduces reproduction and survival rates. In the Cascade Range of central Washington, American Pikas (Ochotona princeps) colonize rock embankment used for stabilization along Interstate 90 (I90). These small mammals live in an environment that presents multiple potential stressors, including road noise, pollutants, modified temperatures, and altered predation pressure. Pikas have low mobility, chronically exposing them to these potential stressors. Long-term monitoring shows that individuals survive multiple years and reproductive females have been found. However, no research to date has determined the fitness of this population. Our objective was to quantify stress levels of pikas along an interstate and assess possible causes of stress. We compared chronic stress levels of pikas living in 3 habitats: (1) rock embankment adjacent to I90, (2) similar rock embankment along a former railroad bed converted to a state park trail, and (3) natural talus patches. To measure chronic stress levels, we extracted fecal glucocorticoid metabolites (GCM) from fresh fecal samples. Glucocorticoids are hormones released when an animal is faced with a real or perceived threat. Fecal GCM are the metabolized product of glucocorticoids excreted in feces as hormones accumulate over the course of a few days. We assessed potential stressors at a subset of sites by measuring subsurface temperatures, elevation, and sound levels. A generalized linear mixed model in R was used to determine differences in GCM concentrations among habitats and assess the potential effects of these environmental variables on stress. Fecal GCM concentrations varied among the 3 habitats. I90 animals had significantly lower fecal GCM levels than pikas in the natural talus habitat; animals along the rail trail had intermediate levels. The variance in stress levels was significantly smaller along I90 than in natural talus. Subsurface temperatures did not differ significantly among all sites sampled. Elevation varied among habitats but showed no correlation with stress. Sound was negatively correlated with fecal GCM. Low fecal GCM in pikas living along I90 may indicate these animals have a suppressed stress response due to chronic exposure to stressors, as seen with European Starlings and Copperheads. Our findings may provide an indicator of stress expected for pikas, and other low mobility small mammals, as they colonize wildlife crossing structures being constructed to improve wildlife connectivity across I90. More research is needed identifying other stressors (air quality, forage availability) and assessing reproductive and survival rates along I90 and other major interstates to better understand the effect of stress on pika fitness in human-modified landscapes.
Terrestrial Wildlife and Ecosystem Interactions with Transportation