Hawks from Every Angle: How to Identify Raptors In Flight by Jerry Liguori, foreword by David Sibley, Princeton University Press, 2005, 132 pages, softcover.
Hawks in Flight: The Flight Identification of North American Migrant Raptors by Clay Sutton; Pete Dunne; David Allen Sibley; David Allen Sibley (Illustrated by), Houghton Mifflin, 1989, 272 pages, paperback.
Hawk Watch-A Video Guide to Eastern Raptors - DVD by Richard K. Walton & Greg Dodge. Superb videography and instructional narrative are combined to provide an effective method for learning hawk identification in the field.
Raptors of Eastern North America by Brian K. Wheeler, Princeton University Press, paper-2005; cloth-2003; 456 pages.