Bird Launching into Flight
In addition to the pattern of the flying bird, we interpret the brief flash of white that appears to the left of the tree, just before the bird takes off.
When the fleeing woodpecker in the Luneau video first
appears in view it is jumping away from the tree trunk and turning its
body and tail. Above the tail, part of the bird’s right wing can be
seen as a white triangle with a black patch above.
We interpret this white triangle as a dorsal view of
the bird’s right wing beginning to open as the woodpecker pivots. This
position would be similar to that shown in the two film frames below (A
and B), taken from the Arthur Allen film shot in Louisiana's Singer
Tract in 1935. In such a position, a Pileated Woodpecker wing would be
all black, as shown on figure C (below).
Pattern at rest
This interpretation is further supported by examining the pattern on the wing of a mounted specimen of Ivory-billed Woodpecker, viewed from different angles (see image sequence below).
The proportional amount of white in the folded wing of
an Ivory-billed Woodpecker varies with the angle from which the bird is
viewed. In a woodpecker specimen seen from above the horizontal, the
wing is predominantly black (A, below). But in the same woodpecker seen
from slightly below the horizontal, or if turning away from the camera
as the woodpecker is in the Luneau video, the wing can appear
predominantly white (B).
When the Ivory-billed Woodpecker specimen's wing is
partly hidden by a tree trunk (C), a pattern results that is remarkably
similar to field 33.3 of the Luneau video (D).
A B C D
Could the white patch be the underwing of a Pileated Woodpecker?
Some have suggested that the white in field 33.3 of the Luneau video could be the extended underwing of a Pileated Woodpecker beginning its first full wing-flap. But note that the white “triangle” actually first appears in field 16.7 (below, white bar points to first appearance of wing), and it is not broadly bordered by black, as it would have to be if it were a Pileated Woodpecker underwing. Moreover, the bird is still vertical in fields 16.7 and 33.3, the tail begins to thrust laterally in field 50, and the tail is approximately horizontal in field 66.7. The wing patch turns at the same rate and angle as does the tail. This concerted movement makes sense if the wing above the tail is unfolding and turning with the tail and the body. These postures are consistent with a bird just beginning to open its wings as it launches, rather than a woodpecker already with its wings wide open in flight.
Our interpretation of a woodpecker pivoting its body from vertical to nearly horizontal before extending its wings in takeoff is supported by many videos we have obtained or viewed of woodpeckers launching into flight. Particularly good examples may be seen at www.manybirds.com; see, especially, the clip of Red-cockaded Woodpecker. See also the clips in Comparisons with Pileated Woodpecker in Flight, presented earlier, and the sequence of images below.
The underwing of a normal Pileated Woodpecker taking flight from the trunk would show a white patch at the top, with broad dark border to the left and below. Field 33.3 in the Luneau video (below left) shows exactly the reverse, with a narrow white triangle bordered only at the top by black.
Deinterlaced video stills showing the underwing pattern of Pileated Woodpecker opening its wings along a tree trunk
Pileated Woodpecker wing specimen coming around tree trunk.
Another possibility is that in field 33.3 of the Luneau video a vertically extended underwing of Pileated Woodpecker is seen. In this case, the black above the white triangle could be the black wingtip.
For at least two reasons this hypothesis fails. First,
the tail of the woodpecker is still pointed down vertically in field
33.3, meaning that the body of the woodpecker is perched vertically at
this moment. It is neither anatomically possible nor aerodynamically
accurate for a vertically oriented woodpecker to have its wings pointed
straight up at this moment of a take-off.
Second, the width:length ratio of the white patch in field 33.3 is 1: 3.1. The only view of a vertically extended underwing of Pileated Woodpecker that would yield a white patch near this ratio is a fully lateral view, as in the upper left picture below. But such an angle would also show a very broad black border left of the white patch in field 33.3. No such border exists. To reduce the black border requires that the wing be turned away or towards us as shown here, but this also makes the white wing patch narrower, even less similar to field 33.3 of the Luneau video.
Pileated Woodpecker wing specimen seen under various
angles. The red line indicates the slope of the tree trunk edge of
field 33.3 of the Luneau video. Numbers below pictures indicate width :
Wrist to tail measurements
Having concluded that the white patch to the left of the trunk is
the dorsal wing patch of an Ivory-billed Woodpecker launching into
flight, with the tail beginning to jut out below, we can make a
measurement that approximates the wrist-to-tail length of the bird on
the tree. By measuring this distance relative to the diameter of the
trunk where the bird is perched, we can convert this measurement into
an absolute measure of wrist-to-tail length.
Zoomed segment of fields 33.3 and 50 from the Luneau video, two consecutive fields in which the woodpecker's right wing is revealed immediately before flight. The large white area represents a dorsolateral view of the secondary flight feathers. The red line on each field marks the exposed distance between a spot near the bird's wrist and the tip of its tail, which is thrusting laterally upon takeoff. Parallel blue and yellow bars identify two diameters of the tree trunk, measured later for scale. Measurement of the tree trunk at the mid-point where the bird took off (photo above, far right) shows it to be 32 cm in diameter.
In Figure S4 in Fitzpatrick et al. (2005) (above) we demonstrated
that the wrist-tail distance of the bird in the Luneau video is in the
range of 34-39 cm. This is entirely consistent with Ivory-billed
Woodpecker and too large for Pileated Woodpecker, which measures 26-31
cm from wrist to tail tip.
Size of white wing patch on launching bird
The size of the white wing patch in the folded wings of Ivory-billed Woodpeckers varies considerably among individuals, as demonstrated by these specimens (below) from the American Museum of Natural History.
Two consecutive film frames (below) show a male
Ivory-billed Woodpecker, first with fully folded wings and then in the
first phase of wing extension. Note that during this wing extension,
the sizes of the wing patches increase by 11 and 17 %.
"Our estimates of the size of the white wing patch in field 33.3 of the Luneau video range from 15.5 to 17.5 cm, depending on how much of the edge-blur we include in our measurement of the white. These measurements are near the upper end of the range for Ivory-billed Woodpecker specimens with tightly folded wings, but are well within the range for measurements with the wing marginally opened, as we believe them to be in the Luneau video (see figure below).
Frequency distribution of length of white wing patches on museum
specimens of Ivory-billed Woodpeckers (N= 54 males, 48 females; sexes
pooled). The white was measured along its long axis parallel to the
wing chord, from the base of white on the secondaries to the
distal-most point on secondaries or primaries, on wings tightly closed
(red bars), and from the base of the innermost white secondaries to the
distal-most white on the primaries, with the primaries gently forced
open to the extent each specimen allowed (blue bars). Black bar shows
our estimate of the size of the white wing patch in the Luneau video
(Field 33.3; the range reflects extremes in the area of measurement
within the blurred edges of this white patch).
Continued on next page