This figure can only be guessed at. Most scientists agree with the bird expert James Fisher, who estimates that there are about 100 billion birds.
Of that number, about 6 billion are said to make their home in the United States. When scientists try to estimate how many different kinds of birds there are, they run into trouble.
Not everybody agrees on what bird belongs to what species. The number most people agree on is 8,600 different species on earth. Of these, the United States has 650 different kinds.
Whoever said the world is for the birds wasn’t too far wrong.