Given the overwhelming popularity and extraordinary usefulness of Cornell Lab of Ornithology’s All About Birds web page, it isn’t surprising at all that the content of it would eventually be employed for the creation of a printed field guide.
When it comes to identifying raptors on the wing – or for that matter most any North American bird in the midst of more or less any other activity – there are few who can rival Pete Dunne in accuracy. His “Hawks in Flight; The Flight Identification of North American Migrant Raptors,” written with David Sibley and Clay Sutton, has become veritably canonical for bird watchers.