Leonardo da Vinci studied birds’ flight for his ornithopter designs.
An ornithopter is a machine intended to fly by flapping wings, rather than by using fixed wings or a rotating rotor. Leonardo investigated bird anatomy, wing structure, balance, and the movement of air while developing several flying-machine concepts. His notebooks include observations of birds and proposals for machines with flapping wings.
Leonardo understood that human muscles alone could not easily power a large flapping aircraft. Some of his designs therefore included mechanical assistance, while others remained studies of anatomy and motion. None of his ornithopters achieved sustained human flight.
Bats also appear in discussions of Leonardo’s flying machines, especially because their wing membranes and skeletal arrangement offered useful design ideas. However, when the question asks which animal’s flight he studied for ornithopters in general, birds is the standard answer. The term itself comes from Greek words meaning “bird” and “wing.”