Non-invasive monitoring of physiological stress in the Western lowland gorilla (Gorilla gorilla gorilla): Validation of a fecal glucocorticoid assay and methods for practical application in the field

► We validated a group specific fecal cortisol metabolite (FGCM) assay for the lowland gorilla. ► A field hormone extraction method performed as well as a laboratory method. ► Dried FGCM extracts at ambient temperature were equally stable as fecal extracts stored at −20 °C over 1 yr. ► FGCMs in alcohol were stable up to 28 days at ambient temperatures. ► FGCMs in un-preserved gorilla feces degrade to 50% of original value over 6 h.