Leonardo da Vinci’s ornithopter designs mainly imitated bird flight.
An ornithopter is an aircraft intended to fly by flapping wings rather than by using fixed wings or a conventional propeller. Leonardo studied birds closely and produced sketches of wing mechanisms, harnesses, and frames intended to transfer human effort into flapping motion.
His designs were important studies of aerodynamics and anatomy, but they were not practical human-powered aircraft. Human muscles cannot normally supply enough sustained power to lift a person with a flapping machine of the kind Leonardo proposed.
Leonardo also explored gliding and other forms of flight, so not every flying-machine sketch was an ornithopter. The defining feature is the planned flapping movement, not simply the presence of wings.