Climate change means springtime's arriving earlier across North America. But the season's onset isn't changing at the same rate across the nation. "Spring is not advancing as quickly in southern regions as it is in northern regions." Eric Waller, a biogeographer at the U.S. Geological Survey. He and his team analyzed more than a hundred years of data on when the first leaves and flowers emerge across North America. And they found that although spring has sprung earlier nearly everywhere, in certain wildlife refuges, the season hits extremely early. And that mismatch could be a problem for migratory birds, who might leave their temperate overwintering grounds down south at the usual time, only to find they've arrived up north too late. "Their food resources might be withering and they might not have as much food available to them. And that could affect their reproduction, their breeding." The analysis is in the journal PLOS ONE. The upshot: it may be more difficult than we thought to predict the effects of climate change on migratory birds. But the data might help land managers decide which plots of land to acquire, to augment existing reserves—and in doing so, ensure that even later birds still get the worm.