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America's Corn Belt acts as barrier for migrating songbirds

The vast agricultural landscape of the U.S. Midwest, known as the Corn Belt, acts as a barrier for migrating landbirds, causing them to adjust their flight behaviors similar to when crossing natural barriers like the Gulf of Mexico, according to a study from the Cornell Lab of Ornithology.

In research in the journal Conservation Biology, the team analyzed five years of weather radar data from 47 stations across the eastern United States to examine how birds modify their migration patterns when crossing the Corn Belt, compared to more forested landscapes.

They found that birds fly faster and are more selective about flying with favorable tailwinds when crossing the Corn Belt—a vast agricultural region where more than 76% of the original forests and grasslands have been converted primarily to cornfields since the 1850s.

"Birds are showing clear behavioral changes when crossing this agricultural landscape compared to more forested landscapes," said lead author Fengyi Guo, a postdoctoral researcher at the Cornell Lab of Ornithology. "They increase their powered flight speed and carefully adjust their flight time and height to take advantage of tailwinds, much like they do when crossing natural barriers like the Gulf of Mexico."

However, unlike the trans-Gulf migration, during which birds must make a nonstop flight, the Corn Belt's scattered forest patches appear to serve as important "stepping stones" where birds can stop to rest and refuel.

"For those birds that do not cross the Corn Belt in a single flight, the radar pattern also shows that they are more likely to make stops in areas with more forest cover within the Corn Belt," Guo said.

This research shows that human changes to the Corn Belt landscape can alter migratory behavior.

"What makes the Corn Belt a somewhat easier barrier to cross (than the Gulf of Mexico) is its narrower width, the presence of forest fragments throughout the agricultural matrix, and the fact that birds can land if needed," Guo said. "Still, we found that birds tend to concentrate in areas with more forest cover within the Corn Belt, highlighting how important these remaining woodlands are for migrating birds."

The researchers recommend protecting existing forest patches and restoring additional forest "stepping stones" within the Corn Belt to help birds successfully navigate this agricultural landscape. They also emphasize the importance of preserving woodlands along the Gulf Coast where birds make the first landfall after crossing that natural barrier.

"With continuing agricultural expansion and coastal development, both the Corn Belt and Gulf Coast are becoming increasingly challenging for migrating birds," said co-author Adriaan Dokter, research associate at the Cornell Lab. "Conservation efforts should focus on maintaining and creating high-quality stopover habitats in both regions to support the billions of birds that migrate through them each year."