Transcription: As a duck's wings make a downstroke, the air pressure on the underside of the wing forces the feathers on the trailing edge into a tight fan. On the upstroke, the feathers open like slats on a Venetian blind to let the air through and decrease resistance to the lifting of the wing. Smooth airflow over and under the wing allows for forward flight. A bird lands by dropping its tail and setting its wings more vertically to reduce speed.
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