The American Ornithologists’ Union is nothing less than the oldest and largest organization in the New World devoted to the scientific study of birds. The AOU has roughly 4,000 members. While most of these are professional scientists, the AOU welcomes any individual dedicated to the advancement of ornithological science.

The AOU identifies its primary activity as the publication of scientific information relating to birds. The Auk, their quarterly journal of ornithology, contains the results of original scientific research and book reviews and is one of the foremost in the field. They also issue a host of other publications, all of great interest to the scientific community and less so to the average bird enthusiast. Their most significant contribution to birders is their A.O.U. Check-list of North American Birds; the AOU checklist is the basis for the American Birding Association checklist. The ABA checklist is the standard for birders throughout North America. Therefore, if you appreciate listing guidelines provided by the ABA (and who doesn’t really?), you can also thank the AOU.