We affect nature and birds in so many ways, not just from oil spills:

"Klem’s 1990 estimate was 100 million annual bird necks broken from flying into glass. He now believes that 10 times that many--I billion in the United States alone--is probably too conservative. There are about 20 billion total birds in North America. With another 120 million taken each year by hunting--that same pastime that snuffed mammoths and passenger pigeons--these numbers begin to add up." -Alan Weisman