Dorsal Views Visible During Flapping Flight
Some critics suggest that the extensive white patches visible on both wings in the Luneau video can be explained entirely as the bird's underwing surface, as this surface is often visible on a flying bird seen from caudal view. However, many studies of flapping flight in birds reveal that the dorsal wing surface is prominently visible from behind on each wingbeat, especially during the upstroke and immediately prior to the power motion of the downstroke. This is nicely illustrated by a clip of Franklin's Gull (Larus pipixcan) as it takes off rapidly from the water, showing both ventral and dorsal surfaces of its wings. Note especially that the upper surface of the left wing is visible at the top of each upstroke, showing the white trailing edge extending to the body. This is the same wing position in which we see white on the upper surface of the bird’s left wing in many frames of the Luneau video.
You can scroll manually through these video clips by moving the round button at the bottom of the QuickTime movie frames with your mouse, or by using the left-arrow and right-arrow keys on your keyboard. This will allow you to see the individual video frames and see the pattern on the wings in various positions during slow-motion flight.
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