Variation of hair cortisol in two herds of migratory caribou (Rangifer tarandus): implications for health monitoring

Abstract

Migratory caribou (Rangifer tarandus sspp.) is an ecotype of conservation concern that is experiencing increased cumulative stressors associated with rapid climate change and development in Arctic Canada. Increasingly, hair cortisol concentrations (HCCs) are being used to monitor seasonal hypothalamic–pituitary–adrenal axis activity of ungulate populations; yet, the effect of key covariates for caribou (sex, season, sampling source, body location) are largely unknown. The objectives of this research were 4-fold: first, we assessed the impact of body location (neck, rump) sampling sites on HCC; second, we assessed key covariates (sex, sampling method, season) impacting HCCs of caribou; third, we investigated inter-population (Dolphin and Union (DU), Bluenose-East (BNE)) and inter-annual differences in HCC and fourth, we examined the association between HCCs and indices of biting insect activity on the summer range (oestrid index, mosquito index). We examined hair from 407 DU and BNE caribou sampled by harvesters or during capture-collaring operations from 2012 to 2020. Linear mixed-effect models were used to assess the effect of body location on HCC and generalized least squares regression (GLS) models were used to examine the impacts of key covariates, year and herd and indices of biting insect harassment. HCC varied significantly by body location, year, herd and source of samples (harvester vs capture). HCC was higher in samples taken from the neck and in the DU herd compared with the BNE, decreased linearly over time and was higher in captured versus hunted animals (P < 0.05). There was no difference in HCC between sexes, and indices of biting insect harassment in the previous year were not significantly associated with HCC. This study identifies essential covariates impacting the HCC of caribou that must be accounted for in sampling, monitoring and data interpretation.

An integrative and multi-indicator approach for wildlife health applied to an endangered caribou herd

“…There are no reference values for hair trace minerals in caribou and we can only compare our results with those from other Rangifer populations. Most element concentrations in the DU caribou were lower than those in a domestic reindeer herd from the University of Calgary (unpublished results, neck location n = 13, medians Ca: 1565.51; Mn: 2.62; Fe: 34.53; Zn: 114.25; Se: 0.52; Mo: 0.24 ppm), and Se was lower than the Bluenose East herd (comparison only with neck location, Se: 0.39 ppm) 31 . In a northern contaminants study of the DU caribou, Cu and Se in kidneys of bulls were lower than those in other barren-ground caribou herds 53 .…”

“…Cortisol concentrations in DU caribou hair and feces had a peak at the beginning of the study period and decreased over the years. Hair cortisol most likely reflected cumulative stressors during the main hair growth period (summer), or perhaps throughout the year 31 , yet a significant decrease was documented. This pattern followed by both faecal and hair cortisol is coincident with the most accelerated declines of the DU caribou herd and the subsequent stabilization in the last population estimates, between 2018 and 2020, at low numbers.…”

“…Fecal stress hormone levels reflect physiological status from approximately the last 24–48 h before sample collection. Hair values largely reflect the accumulation of cortisol during the hair growth period from late spring to fall, representing conditions over several months during the previous summer and fall, and possibly also reflecting stressors during the non-hair growing season 31 . Cortisol concentrations (hair from the neck) and corticosteroid metabolites (feces) were quantified by enzyme immunoassay 32 (Supplementary Appendix S3 ).…”

“…Hair cortisol from 2015–2017 to 2018–2021 was analyzed in different laboratories (Supplementary Appendix S3 ). Part of the results on hair cortisol were previously published 31 .…”