... I'm a researcher whose field of study includes animal movement and migration — Hugh Dingle is one of the premier scientists in this field of study, and this book is THE seminal work on the topic. I reference it regularly.
Rather than just describing all the different examples of migration, Hugh attempts to unify the field under one comprehensive theoretical framework. He succeeds magnificently, starting with an explicit working defininiton of what migration is, then using this to discuss the physiology, mechanisms, and evolution of this behavior. The book is filled with fascinating examples from the scientific literature that clearly illustrate the points he is trying to make. If there are gaps in the story, it is no fault of the author — there are many gaps in our knowledge. ...Hugh is obsessed with insects, there is a good reason for that. Insects make excellent test subjects for these studies — they perform impressive migrations, they are easy to deal with, and easy to manipulate experimentally. Consequently, a great deal of migration research has involved one kind of insect or another.
The book is articulate and highly readable, though I agree that a good background in the biological sciences will help. It is not intended for the casual reader. I highly recommend it (five stars isn't enough), though, for anyone who wants to really delve into the subject.