Pereira, P., Fandos Esteruelas, N., Nakamura, M. et al. 2022. Hair cortisol concentration reflects the life cycle and management of grey wolves across four European populations. Scientific Reports 12(1), 5697.

Hair can be preferred over other biological matrices for ethical reasons. Hair samples can be obtained non-invasively, thus addressing the pressing issues of animal welfare in wildlife research. Additionally, hair collection is simple and inexpensive when performed on specimens in archives and on recently dead animals. This facilitates achieving larger sample sizes and wider spatial–temporal coverage than with invasive sampling. Cortisol in blood or feces reflects the activation of the HPA axis from minutes to a few days before sample collection. In contrast, cortisol is hypothesized to be integrated into the hair over a longer time frame, providing a picture of the activation of the HPA axis over a time frame of weeks to months. Hence, this method offers an opportunity to study the physiological responses of wildlife to natural processes and potential long-term stressors such as social interactions, infectious diseases, or human perturbation. Our aim was to assess the effects of intrinsic and methodological determinants on the hair cortisol concentration (HCC) of wolves from four European populations under different legal management. We determined HCC by an enzyme-linked immune assay in 259 hair samples of 133 wolves from the Iberian, Alpine, Dinaric-Balkan, and Scandinavian populations. The HCC showed significant differences between body regions. Mean HCC in lumbar guard hair was 11.6 ± 9.7 pg/mg (range 1.6–108.8 pg/mg). Wolves from the Dinaric-Balkan and Scandinavian populations showed significantly higher HCC than Iberian wolves, suggesting that harvest policies could reflected in the level of chronic stress. A significant negative relationship with body size was found. The seasonal, sex and age patterns are consistent with other studies, supporting HCC as a biomarker of chronic stress in wolves for a retrospective time frame of several weeks.