Bird migration is the one truly unifying natural phenomenon in the world, stitching the continents together in a way that even the great weather systems, which roar out from the poles but fizzle at the equator, fail to do. Scott Weidensaul follows the awesome kettles of hawks over the Mexican coastal plains, the bar-tailed godwits that hitchhike on gale winds 6,000 miles nonstop across the Pacific from Alaska to New Zealand, and the myriad songbirds whose numbers have dwindled so drastically in recent decades. Migration paths form an elaborate global web that shows serious signs of fraying, and Weidensaul delves into the tragedies of habitat degradation and deforestation with an urgency that brings to life the vast problems these miraculous migrants now face.