Caribou movement as a correlated random walk

Movement is a primary mechanism coupling animals to their environment, yet there exists little empirical analysis to test our theoretical knowledge of this basic process. We used correlated random walk (CRW) models and satell ite telemetry to investigate long-distance movements of caribou, the most v agile, non-volant terrestrial vertebrate in the world. Individual paths of migratory and sedentary female caribou were quantified using measures of me an move length and angle, and net squared displacements at each successive move were compared to predictions from the models. Movements were modelled at two temporal scales. For paths recorded through one annual cycle, the CR W model overpredicted net displacement of caribou through time. For paths r ecorded over shorter intervals delineated by seasonal behavioural changes o f caribou, there was excellent correspondence between model predictions and observations for most periods for both migratory and sedentary caribou. On the smallest temporal scale, a CRW model significantly overpredicted displ acements of migratory caribou during 3 months following calving; this was a lso the case for sedentary caribou in late summer, and in late winter. In a ll cases of overprediction there was significant positive autocorrelation i n turn direction, indicating that movements were more tortuous than expecte d. In one case of underprediction, significant negative autocorrelation of sequential turn direction was evident, indicating that migratory caribou mo ved in straightened paths during spring migration to calving grounds. Resul ts are discussed in light of known migration patterns and possible limiting factors for caribou, and indicate the applicability of CRW models to anima l movement at vast spatial and temporal scales, thus assisting in future de velopment of more sophisticated models of population spread and redistribut ion for vertebrates.