Human disturbance effects and cumulative habitat loss in endangered migratory caribou

As human development intensifies in northern ecosystems, negative impacts of anthropogenic disturbances on wildlife could increase. Many caribou and reindeer populations are declining across the northern hemisphere, and human disturbances have been suggested as a potential cause for these declines. We evaluated the effects of human disturbances in the summer and winter ranges of two migratory caribou herds in northern Quebec and Labrador, Canada. We captured and collared 510 caribou between 2009 and 2015. We first assessed caribou avoidance of human disturbances at a large spatial scale by comparing the density of mines, mining exploration sites, power lines, roads and human settlements within seasonal ranges to their density within available ranges. We estimated the area avoided by caribou (ZOI; zone of influence) around disturbances located within seasonal ranges and evaluated the resulting cumulative habitat loss. We also evaluated the barrier effect of roads and their influence on caribou movement rates. The density of many disturbance types was lower within caribou seasonal ranges than within available ranges, suggesting they avoided disturbances over a large spatial scale. Within seasonal ranges, caribou avoided all disturbance types except power lines. ZOIs were highly variable among disturbance types and years, ranging from no avoidance to 23 km. Cumulative habitat loss could reach as much as 30% of seasonal ranges and 38% of high-quality caribou habitat. We demonstrate that human disturbances have broad negative effects on caribou behavior, but whether this could translate into population decline remains to be investigated.