Wow! As a longtime birder, I know quite a lot about birds but his intimate descriptions of migration is exciting to read, and I recommend this book to birders AND non-birders.
As to his comments on migrations of other wildlife: I did an Earthwatch expedition on 1000 lb leatherback turtles in Costa Rica. The scientist asked the government to ban poachers on the beach during nesting season, but was told there were over 1000 nesting each year. When we put ID's on the females, we found each nested 8 or 9 times every other year - so there were only about 200!. Then when we put satellite tracking on them, we found that the C.R. turtles went south to Ecuador, and ones feeding off Monterey, CA, where they thought ours went, were actually from Indonesia!