The bald eagle is officially the national bird of the U.S.
North American migratory birds getting smaller, their wings wider due to climate change according to study by University of Michigan published in journal 'Ecology Letters'.
The American Bird Conservancy released a study indicating that the bird population in North America had reduced by around 3 billion.
Researchers discovered that as many as 600 million birds die in the US every year after flying into skyscrapers.
San Francisco's skies went dark after millions of birds flew across the city's western side.