Caribou encounters with wolves increase near roads and trails: a time-to-event approach

1. Caribou and reindeer Rangifer tarandus are declining across North America and Scandinavia in part from wolf Canis lupus-mediated apparent competition with more abundant ungulate prey species. While caribou generally persist in areas with low wolf density, wolf packs that overlap caribou ranges could trigger caribou declines. Moreover, anthropogenic linear features such as roads, trails and seismic lines are hypothesized to increase predation risk for caribou, yet few studies have examined the mechanistic effects of linear features or spatial overlap on wolf-caribou encounter rates and predation risk. 2. We used (a) time-to-event models of wolf-caribou encounters estimated from concurrent global positioning system (GPS) radio-collar data from wolves and caribou and (b) wolf resource selection models of travel locations, to determine the potential influence of wolf-caribou spatial overlap, linear features, elevation and season on encounter rates. Analyses were based on data from 35 adult female caribou and 37 male and female wolves from 11 wolf packs from Banff and Jasper National Parks, Canada, from 2002 until 2010. 3. Wolf-caribou encounter rates increased with high wolf-caribou overlap, proximity to linear features and lower elevations. Wolves strongly selected low elevations, especially during winter and spring. Selection for linear features as travel routes increased with elevation. 4. Caribou risk of encounter was highest during the summer and autumn when wolves spent the most time at high elevations. Most wolf-caused mortalities (n = 12) occurred during spring and summer. 5. Synthesis and applications. The presence of anthropogenic linear features and the amount of time wolves spend in caribou range could be equally as important as wolf density when prioritizing caribou recovery actions such as wolf or primary prey reductions or re-introductions. The use of GPS locations and time-to-event modelling offers a powerful tool for evaluating factors affecting predation risk of threatened and endangered species.