Mostly I enjoyed this book, although the sharp transitions from dry scientific exposition to breezy asides sort of threw me for a loop. This is, I suppose, one of the dangers in trying to write popular science books: you want the reader to feel like he's learning something, but not like he's reading a textbook. It's a delicate balance.
I found Tudge's final chapter, which serves as a sort of call to arms on conservation funding and efforts, the most compelling section of the book, and I'm sure for people who are looking for a (mostly) accessible introduction to ornithology this would probably serve quite nicely.