Long distance migrations by large mammals are increasingly imperiled by human development. We studied
autumnmigratory patterns of caribou (Rangifer tarandus) in relation to an industrial road in northwestern Alaska.
Webuilt nullmovementmodels 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 (slowcrossers) and
those that did not differ from that expected from the null model (normalcrossers).We identified eight as slowcrossers
and 20 as normalcrossers. Slowcrossers took an average of 33.3±17.0 (±SD) days to cross the road compared
to 3.1± 5.5 days for normalcrossers. Slowcrossers had an average crossing date of 8 Nov. ± 7.7 days versus 25
Oct. ± 20.6 days for normalcrossers. Movement rates of the two classes did not differ before crossing the road,
but slowcrossers moved N1.5 times as fast as normalcrossers 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 normalcrosser. 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.