As autumn deepens in the subarctic mudflats of Alaska’s Yukon-Kuskokwim Delta, a quiet physiological revolution takes place. A medium-sized wading bird, the bar-tailed godwit ( Limosa lapponica baueri ), prepares for one of the most grueling athletic feats in the natural world. Within weeks, these birds nearly double their body weight, packing on layers of high-density fat that will serve as fuel for an uninterrupted journey across the vast, featureless expanse of the Pacific Ocean. This is not a journey taken in easy stages. The godwits do not glide, nor do they soar on thermal updrafts like eagles; instead, they flap their wings continuously for up to eleven days and nights without a single moment of rest, sleep, or hydration. Recent tracking data from the past year has illuminated the extraordinary sensory and physiological mechanisms that allow these avian mariners to navigate this perilous, trans-oceanic highway. ...