How Birds Rise, Soar on the Wind, and Glide to Rest
Condensing air under the wings to climb; the kite gaining impetus and gliding without beating
A fragment continues a note about the reflex motion made under the wind on the opposite side, then Leonardo explains how a bird climbs by beating its wing-tips toward itself and condensing the air between the tips and its breast, whose condensation lifts it. He observes that the kite and birds that beat their wings little seek the course of the wind, flying high when the wind reigns high and low when it reigns low. When there is no wind the kite beats its wings to gain impetus, then glides a long way without beating, resting on the air after the fatigue of the beat, as do all birds that fly in bursts.
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Climbing by condensing air under the wing-tips
To rise, the bird raises its shoulders and beats its wing-tips toward itself, condensing the air interposed between the tips and its breast; the condensation of that air lifts the bird on high.
The kite soaring, gaining impetus, and gliding to rest
The kite and birds that beat their wings little seek the wind's course, flying high or low as the wind reigns high or low. Where there is no wind the kite beats its wings to gain impetus, then glides a long way without beating, resting on the air after its fatigue, as do all birds that fly in bursts.