Social facilitation of risky habitats in woodland caribou: responses to fire and roads

Habitat change and subsequent trophic effects remain the dominant hypothesis for woodland caribou (Rangifer tarandus) population declines. Boreal forests are undergoing rapid changes, including expanding linear features and climate-induced increased wildfire activity. Within these landscapes caribou habitat selection and movement ought to maximize benefits while mitigating costs, e.g. predation risk, but spatial locations are likely not fixed in their cost-benefit ratio. For caribou, costs and benefits may vary seasonally and by social context. To test the effects of season and social context on caribou movement and selection of potentially risky habitats, we used a socially informed integrated step selection analysis (iSSA). We tested responses to two forms of risk in Terra Nova National Park, NL: roads and areas burned 2 - 75 years prior. Caribou avoided areas near roads irrespective of season. Burned area avoidance varied by season and burn age. Caribou avoided roads less and selected burns more in a social context. Social facilitation may permit the use of areas that were functionally unavailable to animals that were not in groups. As the most at-risk populations of woodland caribou exist at low density in highly disturbed landscapes, our results highlight the importance of considering sociality in maintaining access to resources.