This book by Bridget Stutchbury is an excellent introduction to the behavior and social lives of birds. Using North and Central American birds as examples, she explores such topics as mating, divorce, finding territories, migration, and more.
I've read a good bit about bird behavior, but I still found the information presented here fascinating and learned a great deal. Anyone wanting to learn more about how birds live and interact with each other should check it out.
Full Review of The Private Lives of Birds