Validation and utility of hair cortisol analysis as a measure of long-term physiological stress in the Pallas's squirrel Callosciurus erythraeus.

In various mammalian species, there has been an increase in the use of hair cortisol analysis to evaluate long-term stress. This trend is because of some advantages relative to the standard tools, such as hormone analysis using blood, urine, or feces. Here, I carried out assay validation and adrenocorticotrophic hormone (ACTH) challenge to measure long-term stress in Pallas's squirrel Callosciurus erythraeus. In addition, I investigated the effects of sex, body condition, season, and reproductive conditions on hair cortisol concentrations (HCC) in free-living individuals. The assay validation was reported in this study. Hair cortisol concentrations in squirrels given repeated ACTH injections were significantly higher than those that received a single-ACTH injection and a saline injection. I found a negative effect of body condition on adult HCC. In contrast, body condition had a positive effect on HCC in juveniles. I found no effects of other factors in either adult or juvenile squirrels. Furthermore, although I investigated whether reproductive conditions, such as pregnancy, lactation, and non-breeding in females or testis size in males, affected HCC, I found that there were no effects of reproductive conditions. This study validated the assay and utility of hair cortisol analysis to assess long-term stress, and continuous investigation of the relationship between HCC and fitness is important for determining whether hair cortisol analysis is a reliable method for estimating population health in Pallas's squirrels.