Researchers: More than 4 billion birds stream overhead during fall migration

Fewer birds return to their breeding grounds after going through fall migration and spending months on their wintering grounds. But the researchers were surprised to find that the migrants arriving across the U.S. southern border had an average return rate of 76 percent during the 5 years of the study (2013 to 2017) and the birds wintering in the U.S. had only an average return rate of 64 percent.

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