• We have developed an enzyme-linked immunoassay-based technique to measure hair cortisol concentration (HCC) in caribou.
• A minimum sample quantity of 100 mg hair (approximately a 2 cm by 2cm plucked or shaved patch of hair) is required for cortisol analysis.
• In general, assay performance in Rangifer is in line with our previous work in other wildlife.
• The high extraction efficiency (102.16 ± 5.20%) and low intra-assay coefficient of variation (CV=6.04%) indicate that the technique is accurate and precise.
• Inter-assay CV identified in caribou is greater than that observed in our work with other species but is still within acceptable limits.
• Parallelism between serially-diluted hair extracts and cortisol standards (r2=0.998, P< 0.0001) suggest that the assay is highly specific for cortisol.
• A low detection limit (0.32 pg cortisol per mg hair) indicates the technique is sensitive across the range of HCC determined in caribou to date (mean= 2.22 pg/mg, range= 0.60-6.90 pg/mg, n= 125).
• HCC varies among body regions in caribou. Owing to its low intra-region variability, we recommend collecting only shoulder or rump hair for HCC analysis.
• HCC does not vary with sex class in captive animals.
• HCC varies with age class in some free-ranging herds.
• HCC in quiescent hair is not influenced by adrenocorticotropic hormone (ACTH) challenge, a procedure that mimics short-term stress.
• Hair cortisol concentration is a promising measure of long-term stress in Rangifer.

Applications

Through this project, we are essentially developing and validating a new tool - a biomarker for long-term stress - to be used for the conservation of caribou. We anticipate this tool will be used by others to:

• Provide baseline background data needed to quantify the impact of human land use activities.
• Provide knowledge that is currently lacking to establish cause and effect between large-scale, human-caused environmental change and wildlife population declines.
• Provide "early warning" of potential negative impacts on wildlife population dynamics before they occur.
• Provide data needed to develop predictive models quantifying the response of wildlife populations in altered environments to understand how future problems can best be avoided.
• Evaluate the efficacy of conservation actions.