Like one of the other reviewers, I also found this book an entertaining and informative read. It's a book written for a popular audience, so all kinds of readers should find something in this book.
While there are a few facts that Weidensaul could have attended to a bit more closely (Florence Merriam first published her first field guide, Birds Through an Opera Glass, in 1889, not 1899, for instance) ... the chapter discussing David Allen Sibley's guides is outstanding. Weidensaul interviewed Sibley for the book and, as a result, is able to tell the story of how Sibley's field guides came into being, were designed in the ways that they were, and function as texts.
I'm surprised Weidensaul does not attend more to American women writers such as Neltje Blanchan, Mabel Osgood Wright, and Olive Thorne Miller. These authors all published books about birds in the late 1800s and early 1900s, and to have included them in this story would have, I think, made Weidensaul's history of birding appear to have been less of a story about "great men."
With all of that said, Weidensaul's book is very compelling, personal, and full of facts. He ends making a very strong call for bird preservation in the book, claiming that birders could learn a lot from hunters (among which he counts himself a member). Birders in general have become so concerned with identifying birds that we've forgotten to spend as much or more effort preserving birds, Weidensaul claims. Without the birds, Weidensaul reminds us, we'd have nothing to look at and listen to.