Birds descend from dinosaurs who developed feathers. Those allow most of them to fly, which few other vertebrates can. Some birds gave up flying, like penguins, who specialize in diving and prove feather's fabulous insulating efficiency. Feathers are also key to courting, almost as varied as bird physiognomy and ways of solitary or social life almost all over the globe.
Stars: David Attenborough, Barrie Britton, Stephen Lyle