Barrier impermeability is associated with migratory ungulate survival rates

Barriers can affect the movement, migratory patterns, and demographic rates of ungulates. Even in highly remote areas with relatively little development, like northwest Alaska, isolated roads can alter the movements of ungulates such as caribou (Rangifer tarandus). Here, a solitary, 80-km long industrial road connecting a large zinc and lead mine to a port affects caribou migrations. Using location and survival data from 366 GPS collared, adult female caribou representing > 850 caribou-years from 2010 to 2023, we assessed whether caribou whose fall movements were altered by the road experienced higher mortality risk compared to those whose movements were unaltered. Of the 101 caribou-years that came within 20 km of the road, 58% displayed altered movements. The survival rate of caribou whose movements were unaltered by the road was 20% higher than those caribou whose movements were altered by it, though difference was not significant (p > 0.05). Increased movements, delayed migration, and/or changes in habitat selection related to altered movements could still have energetic and demographic consequences. Caribou that crossed or circumvented the road had significantly higher survival rates (78.5% survived until calving) than caribou that did not cross or circumvent the road (i.e., it acted as an impermeable barrier and the caribou wintered north of it; 57.9%). Given our results, we posit that enhancing the permeability of roads could improve the survival of caribou in the region.