Based on historical accounts of a duck-like flight, the flap style of the Ivory-billed Woodpecker was thought to be duck like, with the wings remaining extended throughout the flap cycle. Details about the flap style are absent from most historical accounts, but a description by Eckleberry (1961) of a “straight ducklike flight in which there seemed to be very little movement of the inner wing” seems to suggest duck-like flaps. In recent years, Hill et al. (2006) reported a “loon-like flight with stiff wingbeats,” which also seems to suggest duck-like flaps. In a painting of woodpeckers in flight by Julie Zickefoose, who painted the cover of the leading contemporary text on the Ivory-billed Woodpecker (Jackson 2004), the Pileated Woodpecker is correctly shown folding its wings against the body in the middle of the upstroke, while the Ivory-billed Woodpecker is shown with the wings remaining extended throughout the flap cycle.

From a vantage point about 75 feet above the water in a cypress in the Pearl River at 8:51 a.m. on March 29, 2008, I spotted a large bird approaching from far down a small channel (see the image above). I initially thought it was a duck based on the speed and directness of the flight. Just before it passed directly below, I saw two white stripes on the back. These field marks are diagnostic of Ivory-billed Woodpecker, but this species was thought to be ruled out after inspecting the video, which revealed a flap style quite different from the expected duck-like flaps. This mystery was resolved when Dalcio Dacol discovered a historical photo of an Ivory-billed Woodpecker in flight with the wings folded closed against the body. This clue about the flap style was apparently overlooked for many years. The 2008 Pearl video was obtained about 840 meters from the site where the 2006 Pearl video was obtained.

Wingspan. In order to estimate wingspan, I returned to the observation position on June 18, 2008, and took photos of a 24-inch reference object. Since the reference photo was obtained after the observation tree had fully leafed out, it was necessary to lean slightly to the side in order to get an unobstructed view of the two large tupelos that were used to scale the reference photo. Since the reference object matches the width of the partially extended wings, it’s clear that the span is significantly greater than 24 inches when the wings are fully extended. The length of the reference object was chosen to be the wingspan of the Belted Kingfisher in order to eliminate that species from consideration.



Flap Style. This movie (half speed) shows part of the cruising flight as the bird approached the observation tree (note that the reflection of the bird from the water is very dark as are the reflections of trees in the image above). This movie (quarter speed) shows part of the cruising flight reflected off the water after the bird passed the observation tree. Note that the wings are folded against the body during the middle of the upstroke. There are only three species that (a) have been recorded in Louisiana, (b) have a wingspan significantly greater than 24 inches, and (c) fold their wings against the body during the flap cycle. There is only one record of Ringed Kingfisher in Louisiana, and that was in the western part of the state. The other species are Pileated Woodpecker and Ivory-billed Woodpecker. In the images below, the top row shows two consecutive frames from the video in which the wings are extended and then folded against the body. The other image in the top row is cropped from a photo obtained by Tanner in 1939 that shows an Ivory-billed Woodpecker in flight with the wings folded against the body. The bottom row shows the reflection of the bird off the water in three consecutive frames that provide a different perspective on the folding of the wings against the body.



Wing markings and other characteristics. The images below illustrate various characteristics of the wings of the bird in the video. The top row shows the reflection of the bird off the water in two consecutive frames in which the wingtips appear to be pointed and swept back. The other image in the top row is cropped from a photo obtained by Tanner in 1939 that shows an Ivory-billed Woodpecker in flight in which the wingtips appear to be swept back. The middle row shows the reflection of the bird off the water in two consecutive frames in which the wings appear to have a high aspect ratio. The other image in the middle row illustrates the relatively low aspect ratio wings of a Pileated Woodpecker. The bottom row shows three consecutive frames in which large white patches are visible on the dorsal surfaces of the wings (dark plumage apparently blends in with the dark mud in the background). The white patches on the wings rule out Ringed Kingfisher.



Wingtip curves. Experts in flight mechanics, such as Bret Tobalske, use wingtip curves to analyze wing motion. Toblaske digitized the wingtip elevation and span from the 2008 video that appear in the top set of curves below. The lower set of curves corresponds to a Pileated Woodpecker (Tobalske 1996). Both sets of curves have the same key characteristics. As indicated by the dashed lines, the span has a small value in the middle of the upstroke and a large value in the middle of the downstroke. The shaded areas indicate brief intervals during which the wings were held fixed in the middle of the upstroke. Such pauses are typical in the flaps of woodpeckers, but they had never been reported for the Ivory-billed Woodpecker.



Flap rate. Two definitions of flap rate are used for woodpeckers since many species have intermittent flights. The raw flap rate is computed by simply dividing the number of flaps by the elapsed time. The intrinsic flap rate is obtained by subtracting out intervals in which the wings are folded against the body. The raw flap rate varies from 6.6 Hz during the approach (15 flaps in 2.27 s) to 7.5 Hz just beyond the observation tree (4 flaps in 0.533 s). This is much higher than any raw flap rate that has been reported for a Pileated Woodpecker in cruising flight. The mean value of the raw flap rate of the Pileated Woodpecker is 3.7 Hz according to Tobalske (1996), and this value is consistent with data obtained by Cornell in Arkansas. For the Pileated Woodpecker, the mean intrinsic flap rate is 5.2 Hz with a 0.4 Hz standard deviation (Tobalske 1996). The intrinsic flap rate of the bird in the video is about 10 Hz, which is more than ten standard deviations greater than the 5.2 Hz mean of the Pileated Woodpecker. The high flap rate of the bird in the video is consistent with Ivory-billed Woodpecker in terms of Tanner’s account of a high flap rate and the predictions of flap rate models.

Flight speed. The bird in the video has a fast and direct flight, which is consistent with historical accounts of the Ivory-billed Woodpecker. Using reference objects that appear in the video and measurements made at the site, I determined that the bird flew about 37.5 m during a 2.48 s interval, which corresponds to 15.1 m/s or 33.8 mph (two similar estimates were obtained using different segments of the flight path). This is the first data-based estimate of the flight speed of the Ivory-billed Woodpecker, which had never before been filmed in cruising flight, and this value is significantly greater than the flight speeds of 7.5 to 11.6 m/s for the Pileated Woodpecker that were reported by Tobalske (1996).

Eckleberry, D. R. (1961). in Discovery: Great Moments in the Lives of Outstanding Naturalists. ed Terres, J. K. Lippincott, New York, New York, USA, pp 195–207.

Hill, G. E., D. J. Mennill, B. W. Rolek, T. L. Hicks, and K. A. Swiston (2006). Evidence suggesting that Ivory-billed Woodpeckers (Campephilus principalis) exist in Florida. Avian Conservation and Ecology 1: on-line.

Jackson, J. A. (2004). In Search of the Ivory-billed Woodpecker. Smithsonian, Washington, D.C., USA.

Tobalske, B. W. (1996). Scaling of muscle composition, wing morphology, and intermittent flight behavior in woodpeckers. Auk 113, 151–177.