Geographic redistributions are insufficient to mitigate exposure to climate change in North American birds.

As climate change accelerates, many species must move poleward or upslope to conserve their environmental niches and limit their exposure. While such geographic redistributions have been extensively reported, an assessment of species' success in limiting their exposure to novel conditions is missing. Here we report on a method to account for biases in tens of millions of species observations and evaluate how 406 bird species native to the United States and Canada have mitigated their environmental niche loss using geographical redistribution. We find that most redistributions have only been partially effective at mitigating exposure to climate change. Over 20 years, species, on average, have redistributed their summertime ranges by ~0.64° north, averting their expected exposure to warming by ~1.28 °C, which is roughly half the warming they would have experienced if they had remained stationary. Meanwhile, species have only mitigated ~0.47 °C (11% of expected warming) in winter, and nearly all have experienced warming of >2 °C. Species moving the farthest north and possessing traits associated with dispersal have succeeded most in limiting their niche loss. Species' historical niches are becoming increasingly mismatched with contemporary climates, even in a highly mobile taxon, raising concerns about the ability of other wildlife to persist in a warmer world.