Using fecal samples to measure physiological stress in American pikas

Background/Question/Methods

The American pika (Ochotona princeps) is considered a sentinel species for detecting ecological effects of climate change.  Pikas are declining within a large portion of their range, and recent research implicates climate change in the extinction of local pika populations.  Pikas have a narrow thermal tolerance; when ambient temperatures increase, pikas reduce their activity levels and rely on access to cooler microclimates within the talus to shed heat passively.  Because pikas behaviorally thermoregulate, it can be difficult to assess the impact of local habitat characteristics on persistence.  We developed a simple procedure designed to provide more direct evidence of physiological stress in pikas.  Pikas were sampled at several locations in the Rocky Mountains, and we measured levels of stress hormone metabolites in collected fecal samples.  Trapped pikas underwent a variety of data collection procedures known to induce stress.  Individuals were held on site for up to 24 hours in a holding 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 once the collection period was over.  Samples were frozen immediately, and later transferred to a lab for extraction and measurement of stress hormone metabolites.  

Results/Conclusions

Analyses of stress hormone metabolites in fecal material are increasingly employed to evaluate stress in sensitive populations of mammals, and concentrations of fecal glucocorticoid metabolites (GCMs) have become one of the best used of these stress metrics.  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.  Results also display individual variation in measured GCM levels, and overall higher GCM levels in samples that had been urinated on when compared to those without urine.  This is the first study to measure stress hormone metabolite levels in fecal samples for any species of pika, and the utility of GCM assays as a metric of stress in American pika populations has now been validated.  Non-invasive collection of fecal samples can be utilized to assess the physiological condition of pikas inhabiting different environments, and to determine whether local habitat variables specifically related to climate can explain levels of physiological stress in pikas.