Birds That Fly by Stars They Can No Longer See
Most songbirds, waders, and raptors that migrate over South Asia do it at night. Darkness gives them cooler, denser air to fly through, fewer predators to dodge, and a sky full of navigational cues, stellar constellations, the faint polarised light at dusk, and the planet's magnetic field sensed through iron-rich cells in their beaks. The bar-tailed godwit, the common swift, the Amur falcon crossing northeastern India toward Africa: all of them read the night sky the way a sailor reads a chart.
