Wingbeat Frequency

Because the bird in the Luneau video flies with rapid, steady wingbeats, we compared its wingbeat frequency with that of known Pileated Woodpeckers and with a measurement of wingbeat frequency from a known Ivory-billed Woodpecker.

The bird in the Luneau video flies in a straight, direct “beeline” flight without changing its wingbeat frequency for 4.5 sec before disappearing among the trees. This direct, powerful, straight-line flight is described by many who see the video for the first time as “duck-like.”  Indeed, the bird in the Luneau video flies with rapid wingbeats in a direct path for the entire time it is in view, completing 8 fully visible wingbeats in about 0.9 seconds, and 10 wingbeats (including two somewhat obscured ones) in about 1.2 seconds. Such escape behavior is extremely unusual among Pileated Woodpeckers, which typically change from a few rapid wingbeats to a slower, swooping or bounding flight soon after leaving their perch. Based on a standard video rate of 29.97 frames per second, we can calculate the wingbeat frequency of the Luneau video bird as follows: using the position where the wings are over the back forming an acute 'V' as an index point for each of eight wingbeats, we observe this position in fields 250 ("0"), 366.7 ("1"), 483.3 ("2"), 583.3 ("3"), 700 ("4"), 816.7 ("5"), 950 ("6"), 1066.7 ("7"), and 1183.5 ("8"). These eight wingbeats span 56 video fields. At 59.94 fields per second, this corresponds to 8 beats in 0.934 seconds, or a wingbeat frequency of 8.6 beats per second.

The wingbeat frequencies of Pileated Woodpeckers in our videos from Arkansas are 2-4 beats per second in level flight (many examples) and 4-7.5 beats for short periods during hasty departures (n = 5). Moreover, experts who have studied Pileated Woodpecker flight using video analysis timed the fastest departures at 7 beats per sec (Tobalske 1996, personal communication). Thus, wingbeat frequency of the woodpecker in the Luneau video is faster than any recorded Pileated Woodpecker.

Remarkably, in part of the historic audio recording of a pair of Ivory-billed Woodpeckers at their nest, the wingbeats of one of the birds flying rapidly from the tree are clearly audible. In this 1935 recording of Ivory-billed Woodpeckers interacting at the nest hole, kent, kent, kent calls are followed by the sound of 8 distinct wingbeats as one Ivory-billed Woodpecker departs from the tree. Tanner described Ivory-billed Woodpecker flight as powerful and unusually noisy. Listen to the recording.

The wingbeat sounds recorded by Arthur Allen and Peter Paul Kellogg in 1935 can be plotted on a sonogram and counted; their frequency is 8.4 beats per second. The frequency of the woodpecker’s take-off flight in the Luneau video is almost identical: 8.6 beats per second.

Sound spectrogram of wingbeats of an ivory-billed woodpecker taking flight, recorded in 1935 at the Singer Tract in Louisiana. The seven wingbeat cycles have a total duration of 836 ms, for an average period of 119 ms, and an average wingbeat rate of 8.4 beats/s.

Female Ivory-billed Woodpecker relieves male at nest in Louisiana in 1935. Photo by A.A. Allen and J.T. Tanner.

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