Why didn’t the caribou (Rangifer tarandus groenlandicus) cross the road? The barrier effect of traffic on industrial winter roads

Barren-ground caribou are in steep decline due to the combined effects of climate change, natural population fluctuations, and anthropogenic disturbance. For the Indigenous peoples that rely on caribou for subsistence and cultural continuity, this decline presents a grave threat to a way of life. Wildlife managers are concerned about the potential effects of winter roads on the use of space by caribou. Roads, especially those with high levels of traffic, act as barriers to movement by ungulates. In the central Northwest Territories, Canada, the Tibbitt to Contwoyto Winter Road services diamond mines located on the winter range of several populations of barren-ground caribou. Impeded movement could restrict the distribution or influence the habitats used by caribou during winter. We investigated the influence of traffic volume and other disturbance and environmental variables on the road-crossing decisions of caribou. We used logistic regression to contrast observed and available crossing events by caribou that were recorded using high-precision GPS collars during 2018–2020. Of 62 collared caribou that moved near the winter road, only 33 crossed the winter road, for a total of 100 crossing events. Caribou rarely crossed the road when any level of traffic was present; the level of traffic, not the road right-of-way, was the underlying explanatory factor for that behavioural decision. Our results suggest that mitigation and associated monitoring should focus on strategies that minimize traffic volume or provide breaks in traffic when caribou are adjacent to winter roads.