Humans use birds for all kinds of reasons, which is a blessing and a curse. They are used for their meat and eggs and for their feathers. Indeed, ostriches and egrets were nearly driven to extinction just because milliners wanted to use their feathers to adorn their hats. Bird guano is used for fertilizer. Many birds are kept as pets, others such as falcons and cormorants are used to help humans hunt and fish. Other birds are hunted. Sometimes, like the passenger pigeon, they are hunted to extinction. Many people simply watch birds and set up feeders in their yards to attract them.