Effects of roads on individual caribou movements during migration

Abstract

Long distance migrations by large mammals are increasingly imperiled by human development. We studied autumn migratory patterns of caribou (Rangifer tarandus) in relation to an industrial road in northwestern Alaska. We built null movement models to determine the expected time to cross the road if caribou movements were not affected by the road. We then identified individuals that took longer to cross than expected (slow crossers) and those that did not differ from that expected from the null model (normal crossers). We identified eight as slow and 20 as normal crossers. Slow crossers took an average of 33.3±17.0 (±SD) days to cross the road compared to 3.1±5.5days for normal crossers. Slow crossers had an average crossing date of 8 Nov.±7.7days versus 25 Oct.±20.6days for normal crossers. Movement rates of the two classes did not differ before crossing the road, but slow crossers moved >1.5 times as fast as normal crossers after crossing the road. Movement patterns were partially explained by environmental attributes, but were most strongly affected by how far a caribou was from the road and whether it was classified as slow or normal crosser. While avoidance is an important aspect of the effects of roads on populations, our results show the importance of other factors, such as how long individuals are delayed in crossing when assessing the influence of development on wildlife.