The U.S. is officially saying goodbye to 21 species that have been feared gone for years. These animals, which include many birds and marine mammals, have been delisted from the Endangered Species Act because they are now declared extinct, the U.S. Fish and Wildlife Service said this week. One famous bird, the ivory-billed woodpecker, was meant to be included in this delisting but has been given another chance, as a group of dedicated birders wage an improbable fight to prove that it may still e