A well-developed and thorough examination of bird migration, including geographical routes, breeding cycles, evolutionary adaptations, wing flap variations, temperature lines, pituitary adjustments and answers to that recurrent question--how do they do it? In proceeding from the observable (where do they go, and why?) to the more complex factors, the author uses specific examples to suggest the range of variations and systematically tracks down natural rhythms and responses to light; inner timing and outside forces; memory and ability to learn. Explicit diagrams and drawings of birds are integrated effectively into the text and a brief, annotated bibliography indicates where to go for more information, even which volumes are available in paperback. This duplicates some of the material in the authoritative chapter in Hyde's Animal Clocks and Compasses on sun and star-pattern directives but omits the names of the researchers. It has the advantage, however, of dealing with the phenomenon as a whole.