Synchronicity of movement paths of barren-ground caribou and tundra wolves

Movement patterns of highly mobile animals can reveal life history strategies and ecological relationships. We hypothesized that wolves (Canis lupus) would display similar movement patterns as their prey, barren-ground caribou (Rangifer tarandus groenlandicus), and that movements of the two species would co-vary with season. We tested for interspecific movement dynamics using animal locations from wolves and caribou monitored concurrently from mid-October to June, across the Northwest Territories and Nunavut, Canada. We used a correlated random walk as a null model to test for pattern in movements and the bearing procedure to detect whether movements were consistently directional. There was a statistical difference between the movements of caribou and wolves (F1,9 = 13.232, P = 0.005), when compared to a correlated random walk, and a significant interaction effect between season and species (F1,9 = 6.815, P = 0.028). During winter, the movements of caribou were strongly correlated with the 80°–90° ($$\overline{X}$$X¯r = 0.859, SE = 0.065) and 270°–280° ($$\overline{X}$$X¯r = 0.875, SE = 0.059) bearing classes suggesting an east–west movement gradient. Wolf movements during winter showed large variation in direction, but were generally east to west. Peak mean correlation for caribou movements during spring was distinct at 40°–50° ($$\overline{X}$$X¯r = 0.978, SE = 0.006) revealing movement to the north-east calving grounds. During spring, wolf movements correlated with the 80°–90° ($$\overline{X}$$X¯r = 0.861, SE = 0.043) and 270°–280° ($$\overline{X}$$X¯r = 0.850, SE = 0.064) bearing class. Directionality of movement suggested that during winter, caribou and wolves had a similar distribution at the large spatial scales we tested. During spring migration, however, caribou and wolves employed asynchronous movement strategies. Our findings demonstrate the utility of the correlated random walk and bearing procedure for quantifying the movement patterns of co-occurring species.