Taking the reader from the mountains of Appalachia to a coffee plantation near Bogotá, Colombia, this investigation into the plight of the cerulean warbler—a tiny migratory songbird—describes its struggle to survive in ever-shrinking bands of suitable habitat. This elusive creature—a favorite among bird watchers and the fastest-declining warbler species in the United States—has lost three percent of its total population each year since 1966. This precipitous decline means that today there are 80 percent fewer ceruleans than 40 years ago, and their numbers continue to drop because of threats including deforestation, global warming, and mountaintop-removal coal mining. With scientific rigor and a sense of wonder, Fallon charts their path across more than 2000 miles and shows how the fate of a creature weighing less than an ounce is vitally linked to that of our own.