Descent Into The Air

Flight evolves in Archaeopteryx; it leaps through treetops in search of insects. Birds are the only dinosaurs which will survive the coming Cretaceous-Tertiary mass extinction. Flight gives birds a leg up: they evolve long-distance seasonal migration, which permits them to respond to Earth's hard times.

Like all migrating animals, birds have a series of preferred and back-up migration systems. They read the stars for orientation; they read the landscape through sounds of water flow and low-frequency sound waves around mountain peaks and passes; they track magnetic fields by use of internal compasses.