Using physiological samples to measure stress in American pikas

The American pika (Ochotona princeps) is considered a sentinel species for detecting ecological effects of climate change, but previous studies have focused on local pika extinction as a metric of change. We have validated simple procedures designed to provide an earlier warning signal, based on non-invasive sampling and analysis of physiological stress in living pikas.  Pikas were sampled at the Niwot Ridge LTER for the measurement of stress hormones (glucocorticoid metabolites, GCMs) in fecal samples as well as glucocorticoid concentration (GC) in plasma samples. Trapped pikas underwent data collection procedures known to induce stress, including blood sample collection via retro-orbital bleeding. Individuals were then held on site for up to 24 hours in a chamber specifically designed for non-invasive collection of fecal samples. Fecal samples were collected every 1-2 hours, and animals were released back into their home territories at the end of the collection period. All samples were frozen immediately, and later transferred to a lab for extraction and measurement. Collected fecal samples were analyzed for GCM concentrations, and comparisons were made between GCM levels measured in samples collected at different times subsequent to capture. Results reflect the expected increase in GCM level following a stressful event, and also identify the time delay (12.5 hours) between a pika’s exposure to a known stressor and subsequent elevation of its GCM level. GC measured in plasma samples reflects individual variation seen in GCM levels, and further validates the techniques used. This is the first study to measure stress hormone metabolite levels in fecal samples for any species of pika. Non-invasive collection of fecal samples may prove useful in assessing the physiological condition of pikas inhabiting different environments, to determine whether local habitat variables specifically related to climate can explain levels of physiological stress in pikas.