Mateo, J.M. & Cavigelli, S.A. 2005. A validation of extraction methods for non-invasive sampling of glucocorticoids in free-living ground squirrels. Physiological and Biochemical Zoology, 78, 1069-1084.
Fecal hormone assays provide a powerful tool for non-invasive monitoring of endocrine status in wild animals. Here we validate a protocol for extracting and measuring glucocorticoids in free-living and captive Belding's ground squirrels (Spermophilus beldingi). We first compared two commonly used extraction protocols to determine which performed best with commercially available antibodies. We next verified the preferred extraction method by correlating circulating and fecal glucocorticoid measures from a group of individuals over time. For this comparison, we used both a cortisol and corticosterone antibody to determine which had greater affinity to the fecal metabolites. Cortisol was the primary circulating glucocorticoid, but unlike in other sciurids both hormones were well above detectable concentrations in the blood. In addition, the cortisol antibody showed greater binding with the fecal extracts than did the corticosterone antibody. Finally we used adrenocorticotropic hormone and dexamethasone challenges to demonstrate that changes in adrenal functioning are reflected in changing fecal corticoid levels. These results suggest that our extraction protocol provides a fast, reliable assay of stress hormones in free-living ground squirrels, without the confound of short-term rises in glucocorticoids due to handling and restraint stress, and can facilitate ecological and evolutionary studies of stress in wild species.