The writer of a field guide to North American birds and three academic colleagues have challenged the videotape evidence offered as proof of the existence of an ivory-billed woodpecker in Arkansas' Big Woods region. Long believed to be extinct, the bird made headlines around the world last April when scientists announced that they had spotted it several times and caught it on film.

But David Sibley and his team argue that the low-quality video shows the more common pileated woodpecker, not the ivory-bill, preparing to take flight from a tupelo tree and then flapping into the distance. The flying bird in the video lacks as many white feathers as one would expect to see on an ivory-bill, they assert. They also dispute that a "vague pale blur" on the bird's back could be the ivory bill's distinctive white stripes, instead ascribing the feature to either the head markings of a pileated woodpecker, sunlight reflected on the bird's back or a flaw in the video itself.

Ornithologist John Fitzpatrick of Cornell University and his colleagues, including engineering professor David Luneau of the University of Arkansas, who shot the video, dismiss these arguments in an accompanying response. Both teams engaged in the kind of frame by frame analysis usually reserved for forensics work. Fitzpatrick's team also used tests with models to disprove Sibley's contentions about the bird's flight mechanics and initial posture--and therefore how much white or black should be visible--and it supplied audio evidence of wingbeats in the same range as an ivory bill recorded in 1935.

Although the teams disagree on the identity of the bird in the video, they concur that the ivory-bill may persist in the southern U.S., and that conservation efforts aimed at preserving its habitat should therefore continue. Both papers appear in the current issue of Science.