Every spring, billions of warblers, thrushes, sparrows, and other small songbirds undertake something remarkable: these thoroughly diurnal creatures — birds that spend their days foraging, singing, and defending territories in broad daylight — flip their internal clocks and launch themselves into the night sky for marathon nocturnal migratory flights. The reasons are compelling and complementary. Nighttime air is cooler and more stable than daytime air, which helps small birds avoid overheating during sustained flight and reduces the turbulence that would otherwise cost them precious energy. Flying in darkness also dramatically lowers their exposure to aerial predators like hawks and falcons that rely on vision to hunt. And by reserving the night for travel, songbirds free up the entire day for foraging at stopover sites — critical refueling stops where they must rebuild fat reserves before the next leg of their journey. Migrating songbirds navigate using the stars, the Earth's magnetic field, and even polarized light patterns at sunset to chart their course across hundreds or thousands of miles.
Researchers continue to learn about how birds prepare for and manage their nocturnal migration journeys. For example, a recent study of free-living Red-backed Shrikes revealed that their migratory flights are organized in a highly structured pattern, with flights grouped into consistent segments that were remarkably similar across tracked individuals.