Hair cortisol concentration in rehabilitating and free-ranging American black bears (Ursus americanus)

Noninvasive measures of health and stress are important in black bear rehabilitation settings to evaluate the impact of short-term managed care and potential for successful release. Increased stress can negatively affect immune function, healing, and growth. Hair cortisol has been evaluated as a marker of long-term stress in several ursid species. This study evaluated hair cortisol concentrations (HCC) of juvenile American black bears (Ursus americanus), undergoing rehabilitation, as a marker of stress during short-term management and compared HCC to that of free-ranging adults. Hair samples were collected upon intake and release of 23 juvenile black bears (n = 11 male, n = 12 female) that underwent successful rehabilitation in the southeastern United States. An additional 28 samples were obtained from free-ranging apparently healthy adult bears examined for management purposes. HCC was measured using an enzyme immunoassay. Statistical analysis showed higher HCC upon intake (median 135 pg/mg; range 6.8–380 pg/mg) compared to release (124 pg/mg; 5.6–152 pg/mg) (P = 0.007) from rehabilitation. No difference was found between intake or release samples compared with free-ranging bears. Sex, age, season, and reason for intake did not have significant effects on HCC. Results of higher HCC upon intake compared to release shows that cortisol decreased during rehabilitation of these bears. HCC should be considered as a non-invasive and objective wellness monitoring tool of rehabilitating black bears in future studies.