Abstract
Investigators of wildlife populations often utilize demographic indicators to understand the relationship between habitat characteristics and population viability. Assessments of corticosterone may enable earlier detection of populations at risk of decline because physiological adjustments to habitat disturbance occur before reproductive diminutions. Noninvasive methods to accomplish these assessments are important in species of concern, such as the greater sage grouse (GRSG). Therefore, we validated a radioimmunoassay that measures immunoreactive corticosterone metabolites (ICM) in fecal samples and used it to characterize the adrenocortical response of 15 GRSG exposed to capture, intravenous injection of 50 IU/kg adrenocorticotrophic hormone (ACTH) or saline, and 22 h of confinement. Those animals injected with ACTH exhibited a more sustained (P = 0.0139) and less variable (P = 0.0012) response than those injected with saline, indicating different levels of adrenocortical activity. We also found that potential field-collection protocols of fecal samples did not alter ICM concentrations: samples held at 4 degrees C for up to 16 h contained similar levels of ICM as those frozen (-20 degrees C) immediately. This study demonstrates a multiphasic adrenocortical response that varied with the level of stimulation and indicates that the assay used to measure this phenomenon is applicable for studies of wild GRSG.