Disturbance and chronic levels of cortisol in boreal woodland caribou

Disturbance by anthropogenic activities may cause chronic (long-term) stress in wildlife and contribute to population declines. Although declines of boreal woodland caribou (Rangifer tarandus caribou) across Canada have been attributed to anthropogenic disturbance, the physiological stress response of caribou to disturbance is not well understood. As a measure of chronic stress, we assessed cortisol concentrations in guard hair from 89 female caribou between 2009 and 2011 in eastern Manitoba. We compared cortisol concentrations among 5 caribou populations occupying areas with varying levels of disturbance, and estimated home ranges of 55 collared caribou to examine how home range size varied with cortisol concentrations. Within each home range, we quantified disturbance characteristics (roads, transmission lines, cottages, and logged and burned areas) and landscape features (lakes, black spruce [Picea mariana], and jack pine [Pinus banksiana]), and used model selection to determine the combination of disturbance features that best explained variation in caribou cortisol concentrations. Hair cortisol concentrations differed among the 5 caribou populations and increased with decreasing home range size. The proportion of the home range logged in the previous 6-21 years best explained variation in cortisol concentrations. Our results suggest that caribou respond negatively to logging, and caribou occupying the southern extent of their range could be vulnerable to disturbance. Although disturbance affects caribou cortisol concentrations, the consequences of increased cortisol concentrations on caribou survival and reproduction are unknown and need to be examined for effective management of populations. (c) 2017 The Wildlife Society. We evaluated the effects of disturbance on chronic levels of cortisol in boreal woodland caribou, and found that cortisol levels increased with increasing logging disturbance and decreasing home ranges. Minimizing logging and other anthropogenic disturbance, particularly from the southern extent of the caribou's range, could reduce cortisol levels in caribou.