Leonardo da Vinci studied birds when designing his flapping-wing ornithopter.
An ornithopter is an aircraft intended to fly by flapping wings, imitating the action of birds or insects. Leonardo filled notebooks with observations of bird flight, wing movement, balance, and the relationship between air and motion. His proposed machines included wings that a human pilot would operate mechanically.
Leonardo understood that merely copying a bird's shape was not enough. A person could not generate the power required to flap wings of the necessary size, so his human-powered designs could not fly. Even so, his studies helped make flight a subject of systematic observation rather than only a matter of myth or speculation.