Pesticides kill 72 million birds directly, but an unknown and probably larger number ingest the poisons and die later unseen. Orphaned chicks also go uncounted.
And then there is flying into objects, which is most likely what killed the birds in Arkansas. The government estimates that strikes against building windows alone account for anywhere from 97 million to nearly 976 million bird deaths a year. Cars kill another 60 million or so. High-tension transmission and power distribution lines are also deadly obstacles. Extrapolating from European studies, the Fish and Wildlife Service estimates 174 million birds die each year by flying into these wires. None of these numbers take into account the largest killer of birds in America: loss of habitat to development.All of this explains why about a quarter of the 836 species of birds protected under th eMigratory Bird Treaty Act are in serious decline. For a third of the other birds there is not enough information to be sure about the health of their populations.
Read full story here. http://www.nytimes.com/2011/01/18/science/18birds.html