It's a yearly occurrence. Birds fly great distances looking for proper food and habitat. But a recent report on bird migration indicates a disturbing trend.
According to the National Audubon Society, more than half of 305 selected bird species in North America are spending winter farther north than they did 40 years ago. Some by hundreds of miles. The birds sampled include purple finch, ring-neck duck, swallows, and other common species.
Bird patterns change. Urban sprawl, deforestation, even backyard feeders affect migration. But researchers say the reason why so many birds are wintering farther north is global warming.
Stephen H. Schneider, of Stanford University: "By looking at melting glaciers, by looking at when plants bloom in the spring and birds come back in migration. They're all consistent. There's a warming trend."
Audubon hopes the report will move the more than 40 million U.S. bird-watchers to help aid conservation efforts and help others recognize the impact climate change is having here and now.