Jan Geisler

Climate change is causing an earlier onset of spring, requiring migratory birds to accelerate their spring migration to avoid arriving late at the breeding grounds. This acceleration hinges on the capacity to shorten the time spent building energy reserves (fuelling) for migratory flight, which is currently thought to be very limited. Combining multiyear global-positioning-system tracking and body mass data from five large-bodied Arctic-breeding waterfowl species, we demonstrate that there is considerable scope for the studied species to migrate faster by shortening the fuelling time, either before departure or at stopovers. With the exception of one species (brent goose), populations were able to largely or fully offset their spring departure date with subsequent fuelling time en route. Still, under the current rates of Arctic warming, this may allow them to mediate only a few more decades of spring advance by migrating faster.