Hawk Migration - websites
Thermals - explanation of thermals and birds - Gary Taylor discusses thermal structure and aerodynamics
Through the lens Radio Controlled Soaring at

Careau, V., J.F. Therrien, P. Porras, D. Thomas, K. Bildstein. 2006. Soaring and gliding flight of migrating Broad-winged Hawks: behavior in the Arctic and Neotropics compared. Wilson Journal of Ornithology 118(4): 471-477.
Hawk Identification Books
A Field Guide to Hawks of North America by William S. Clark and Brian K. Wheeler, Houghton Mifflin, Second Edition (2001).   
Hawks from Every Angle: How to Identify Raptors in Flight by Jerry Liguori, Princeton University Press (2005).
Hawks in Flight by Pete Dunne, David Sibley, and Clay Sutton, Houghton Mifflin (1988).  
Hawk Watch: A Guide for Beginners by Pete Dunne, Debbie Keller, and Rene Kochenberger, Cape May Bird Observatory (2002).  
A Photographic Guide to North American Raptors by Brian K. Wheeler and William S. Clark, Academic Press (1995).

The Crossley ID Guide: Raptors by Richard Crossley, Jerry Liguori, and Brian L. Sullivan

Hawks at a Distance: Identification of Migrant Raptors by Jerry Liguori with a foreword by Pete Dunne
Facebook Hawk ID Group

The Birder's Library has a nice post reviewing the above references.
Paul M. Roberts has a nice post reviewing the above references plus some additional references.

Hawks on the Wing, by Joshua Haas (2015) - a DVD video describing Hawk ID by one of Michigan's own!

Other links
Recent Publications
See Publications in sidebar at left. 
[Last updated 07/2017]