How a bird turns by beating one wing
The beating wing likened to an oar rowed on one side to steer the flight
Leonardo explains how a bird turns in the air: it beats its wings many times on one side only, pivoting about the wing it holds still, rowing the beating wing back toward the tail. He compares this to a boatman who rows repeatedly with one oar on the side from which he wishes to swing away while keeping the other oar motionless. A small sketch of a bird in flight appears at the top of the page, which also carries the stamp of the Institut de France.
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Turning about the motionless wing
To turn, the bird beats one wing many times while the other stays fixed, so that it pivots around the still wing. The beating wing rows toward the tail, exactly as a rower drives a boat by pulling one oar on the side he wishes to leave while holding the other oar steady.