Climate change may be why birds are migrating earlier across the United States
A large-scale analysis of bird migrations in the contiguous United States confirms what ornithologists and amateur birders already suspected: Overall, birds’ seasonal long-distance flights are happening earlier than they did a quarter of a century ago. This shift is probably due to higher temperatures, which have risen on average around half a degree Celsius per decade, researchers report December 16 in Nature Climate Change. Looking back over 24 years, the researchers found that warmer seasons often predicted earlier migrations. One reason for this could be that birds may rely on a variety of cues, including temperature and length of day, to sync their flights with the availability of food and nesting-friendly conditions. Previous studies of individual species have shown that some birds are migrating earlier in the year. But “that you can see these kinds of shifts at a broad scale… it’s a striking statement about how powerful these impacts of climate change can be,” says Andrew Farnsworth, a migration ecologist at Cornell...