If you want to own a book that has every recognized species of bird with every subspecies and where each species and subspecies is found and a nice little space for you to write in the date and location where you first saw or heard the bird, this book is for you (It's definently for me!!!) This is the checklist used by most of the world's top birder's and since the passing of Mr. Clements, the list is now being managed by Cornell University. Another piece of essential birding gear.