Their own video analysis, Sibley's team writes, shows that "all observed features are consistent with a typical pileated woodpecker."
Standing by Their Bird
For their part, the original team that identified the bird as an ivory-bill dismisses the challenge to their finding in a response also published in tomorrow's Science. John Fitzpatrick of the Cornell Lab of Ornithology in Ithaca, New York, led the original team.
Standing by their identification, the researchers argue that their interpretation of the bird's posture is more accurate than Sibley's team's version.
The original posture interpretation, Fitzpatrick's team says, supports their calculations of the extent of white feathers on the bird's back in the video.
They note that white plumage seen on the bird's back doesn't match the pattern of a pileated woodpecker, nor does the absence of black trailing edges on the underwings of the bird in the video.
Fitzpatrick's team concludes that available data on wingspan and flight style does indeed indicate an ivory-billed woodpecker. The researchers also point out that the video was presented to the Arkansas Audubon Society, which voted unanimously to accept it as proof of the bird's existence.
David Luneau, the bird enthusiast who filmed the woodpecker, says Sibley and his colleagues—the skeptics—offer no video evidence to support their contention that some features shown are typical of a pileated woodpecker.
"All of the flight videos of pileateds that we have examined are markedly different in many ways than the bird in the video," Luneau said.
But David Sibley says the burden of proof is on the Cornell-led team. It's up to them, he says, to show that the species is not a pileated woodpecker.
"Nothing in the video is inconsistent with [a] pileated woodpecker, and many of our key points are not refuted by the Cornell team's response," Sibley said. "Therefore the video cannot be proof of the existence of [an ivory-bill]."
Sibley suggests the poor quality of the video may have helped mislead the ornithologists who first studied it.
"The image [of the bird] is extremely small, occupying only a few pixels. It's out of focus, and it's blurred by motion," Sibley added.
Other, unconfirmed sightings of ivory-billed woodpeckers have been reported in recent years. But "without proof, it comes down to a matter of opinion, which is all we've had since the 1940s," Sibley said.
Sound Test
Last year another group of bird experts planned to contest the video evidence. But in August they dropped their challenge after the Cornell lab presented audio recordings taken in the Big Woods region. The audio was suggestive of two ivory-bills rapping on wood.
Richard Prum is an ornithologist at Yale University in New Haven, Connecticut. He said at the time that the sound recordings "provide clear and convincing evidence" that the bird wasn't extinct.
But Sibley said this week, "The Cornell team has always said that the audio evidence is inconclusive. I agree."
According to Luneau, who filmed the bird, there are now "additional interesting sound recordings" which are being analyzed.
Luneau is an associate professor of electronics and computers at the University of Arkansas at Little Rock. He says the results of searches during the fall and winter, when reduced leaf cover makes woodpeckers easier to spot, will be reported soon.
"I am optimistic that there will soon be additional hard evidence," he added.
"The Big Woods of Arkansas is a large area of bottomland forest, much of which is difficult to access," he said. "As John Fitzpatrick said when we began the search in 2004, 'Let's keep in mind that the bird has the upper hand here.'"
Despite their conflicting views, both sets of researchers agree on the need to continue conservation efforts that could benefit the ivory-billed woodpecker.
Whether the ivory-bill is there or not, Sibley said, "The value of saving and restoring the bottomland forest habitat—for other species such as Swainson's warbler, Mississippi kite, and black bear, as well as for our own benefit—is immeasurable."
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