For example about twenty years ago scientists decided the Baltimore Oriole was really the same bird as the Bullock's Oriole. The Baltimore Oriole lives in the Eastern United States and the Bullock's Oriole lives in the Western United States. Both birds were called the Northern Oriole. There seems to be a trend today toward splitting birds. This is because better methods of research are now available to examine birds at the microscopic level.
Today there are many scientists investigating birds.
They work at places like The Academy of Natural Sciences in Philadelphia or Cornell Laboratory of Ornithology or Pennsylvania State University or Louisiana State University. It is certain that their work will make bird species appear and disappear as they continue lumping and splitting. That is why a computerized list of the world's birds makes more sense than a printed list in a book. You can update your computer and always have the best, most current classification list possible. A book listing all the birds of the world is obsolete by the time you read it.