Every autumn monarchs do something no other butterflies do: they migrate unimaginably long distances. Monarchs born east of the Rockies typically go to Mexico. Those born west go for the most part to the California coast, often travelling between 40-50 miles a day, but sometimes as much as two hundred. How do butterflies know when it is time to leave their summer breeding ground, how do they navigate to reach their overwintering sites -- milions and millions returning, every year, to the same unlikely site: an unhospitable 50 acres ofoyamel pine forest, 100,000 feet in Mexico's transverse Neovolcanic mountains. Mernory does not guide them -- as no single butterfly makes the round trip (3 generations separate those that spend the winters in Mexico from those that go there).

In "Four Wings and a Prayer", Halpern recounts the mesmerizing story of this mystery -- how the first clues were pieced together, the discoveries of the Canadian biologist Fred Urquhart and his wife who first encouraged amateur lepidopterists to tag butterflies, to Lincoln Brower, perhaps the pre-eminent monarch scientist, who has first certified the regularity of the monarch's migratory pattern, to Don Davis, tireless tagger, who holds the record for the most monarchs ever recovered in a single year (10) and the monarch that covered the greatest distance (2880 miles). At the same time Halpern conveysthe delicate magic of the butterflies and how each encounter we have with them -- whether with millions or with a single one -- is a moment of transcendent delight.