A pair of whooping cranes look for food at Necedah National Wildlife Refuge in Wisconsin. A new study shows that migrating birds could suffer as climate change shift the onset of spring. (Credit: critterbiz/shutterstock) Thanks to climate change, spring now comes earlier. But how much sooner the season arrives varies across the U.S. That’s according to a new study published Wednesday in the journal PLOS ONE that assessed the first appearance of leaves and flowers in nearly 500 U.S. National Wildlife Refuges over more than 100 years. Researchers found the irregular seasonal changes affect migratory birds' breeding sites, an outcome that could endanger many species.