This is a book for serious birders of the highest order. It's clearly written with ornithologists and animal scientists as the primary audience, but there is a wealth of information in it. If you keep a library, this book will be in it. If your a weekender, it's probably too detailed. If you want to really understand why migration evolved and how it works and what it is all about, then work through this book, which collects the experts in one spot and provides the answers. Pricey, but you get a lot of book.