Ruby-throated hummingbirds are arriving in North America each spring several weeks earlier than in the past, and research indicates that higher temperatures in their winter habitat may be the reason.
Scientists at Clemson University in South Carolina, Taylor University in Indiana and the University of Nebraska have compared recent data showing the birds' first arrival times with information going back to the late 1800s.
The findings show that the tiny birds are arriving from their wintering grounds in Central America 12 to 18 days earlier than in the past.
That could be a challenge for the birds. The scientists say that though warmer weather in Central America may be forcing the birds to fly north earlier, the food they need when they arrive may not be available yet.