A simplified, non-invasive, and reproducible approach to monitoring stress in endangered bats using fecal cortisol assays

Background/Question/Methods Chronic stress in mammals is associated with elevated daily secretion of glucocorticoids.  Cortisol, the major glucocorticoid in bats, is a critical hormone that affects most organ systems and physiological processes. However, chronically elevated cortisol results in immunosuppression, increased incidence of metabolic disturbances, cardiovascular changes, and reduced fertility. Certain stimuli ("stressors") appear to be ubiquitously stressful in mammals. These include loud noise and seismic vibration, which are commonly encountered near military bases, airports, and active surface mines. While most of the circulating glucocorticoids in mammals are excreted in the urine, a small percentage of cortisol and its metabolites appear in the feces in proportion to plasma concentrations. Fecal assays have been developed as an indirect means of assessing stress in free-ranging or endangered mammals, without the need for invasive procedures or blood sampling. As part of a study investigating the response of endangered Indiana bats (Myotis sodalis) to activities associated with military training and operations, we have developed and validated a fecal collection and assay procedure. This procedure allows for multiple fecal samples to be extracted and assayed under a variety of conditions. 

Results/Conclusions To develop and validate this assay for Myotis sodalis, fecal samples were first collected from an abundant, non-endangered cogener, the little brown myotis (M. lucifugus), which served as a surrogate species. The procedure for extracting immunoreactive (ir) cortisol from fecal pellets of M. lucifugus was optimized for collection method, solvent type, duration of extraction, and recovery. Next, the fecal cortisol assay was validated for M. lucifugus by demonstrating an increase in fecal cortisol levels following an increase in plasma cortisol levels resulting from handling/blood-sampling stress. Finally, biochemical validations demonstrated that the assay accurately and precisely measured cortisol concentrations in fecal samples. Using these procedures, the presence of ir-cortisol was then demonstrated in feces from M. sodalis; values ranged from 0.35 to 3.89 ng/mg fecal mass. Continuing studies are being conducted to determine whether bats sampled at military sites have higher fecal ir-cortisol than bats sampled at non-impacted sites. The ability to assess stress is often an important aspect of ecological and conservation research. The procedure reported here will assist field researchers in efforts to quantify the physiological status of free-ranging and endangered bats and other mammals.