What power source did Leonardo da Vinci's ornithopter rely on?

Leonardo da Vinci's ornithopter relied on human muscle power.

An ornithopter is a flying machine that produces lift by flapping wings rather than by using fixed wings or a conventional propeller. Leonardo studied birds and bats and sketched several designs in the late fifteenth and early sixteenth centuries. His concepts included wings operated by a person through pedals, levers, and other mechanical linkages.

Leonardo understood that a machine would need both lift and forward motion, but human muscles cannot provide enough sustained power for a large flapping aircraft carrying a pilot. His ornithopter therefore remained a design study rather than a successful aircraft.

The term ornithopter applies to many later machines, including modern experimental aircraft. Leonardo's design should also be distinguished from his separate aerial-screw concept, which used rotary motion instead of bird-like flapping.