Knock knock, the twitchers are all a-flutter

The ivory-billed woodpecker, feared extinct for 60 years, has been seen in a remote part of Arkansas. Picture / Reuters

The four seconds of blurry videotape has been labelled the twitcher's version of the Zapruder film, the intensely scrutinised footage that recorded the assassination of President John F. Kennedy. Shot from a boat deep in the swamp forests and bayous of the Big Woods of Arkansas, on April 25, 2004, the film provided a tantalising glimpse of a near mythical bird last seen in 1944: the ivory-billed woodpecker.

"A large black and white woodpecker flashed off the side of a tree," says David Luneau, the amateur ornithologist who shot the tape.

Luneau was checking remote sensor cameras, mounted as part of a major ivory bill research project by Cornell University's Lab of Ornithology, when he saw the bird. "I had left my digital video camera running in case I ever saw one," he recalls. "But I had my hands full with a paddle."

Luneau grabbed his camera and pointed it. "The bird was gone in four or five seconds. All I ever saw was the rear view. Pretty much like you see on the video. It was a very unsatisfactory look. The bird became a dot."

Nonetheless, Luneau's footage appeared to confirm two recent sightings of Campephilus principalis - the world's second-largest woodpecker, distinguished in males by a red crest - made in the same area with recordings of the ivory bill's distinctive call and double-rap "drumming", made when the bird hammers its bill into trees for insects.

Announced in the journal Science, the discovery was greeted with hosannas by ornithologists. The "Lazarus bird's" rescue from assumed extinction was likened to finding a dodo. The federal government stumped up US$10 million ($16 million) for ivory bill conservation, and Arkansas reported a 30 per cent jump in tourism as birders homed in.

In an era of escalating species extinction, the woodpecker's dramatic reappearance made world headlines, a good news story and a ray of hope that some species may buck the odds.

That was then. Now comes the letdown. Several sceptical reports have appeared in the past nine months. Last month Science published a frame-by-frame video analysis by David Sibley, the author of The Sibley Guide to Birds, and three fellow ornithologists.

After examining plumage colours visible in the upstrokes and downstrokes of the flying bird, the authors felt the evidence fell short of an ivory bill resurrection.

"The bird is flying away," Sibley tells me. "So the only really useful part is about one second, or eleven wing beats. You can see a lot of white, but you can't be sure which part of the bird it shows. That's the difference between our interpretation and Cornell's. They assume the white is on the upper side of the wing, which would means an ivory bill. We think the white is on the under wing of a pileated woodpecker."

This cuts no ice at Cornell, where the video has been scrutinised almost pixel by pixel. Luneau admits the quality is "lousy," but says repeated examination has only confirmed the belief that Cornell struck gold.

"Our interpretation is that it's an ivory bill," says Ron Rohrbaugh, director of Cornell's Ivory-Billed Woodpecker Research Project. "We've had numerous sightings from experienced wildlife biologists, who are trained observers of birds. Those are definitive, high-quality sightings. And we have acoustic evidence that suggests the bird is there."

Nonetheless, the onus is on Cornell to come up with irrefutable proof. The ivory-billed woodpecker has almost legendary status among American twitchers. Sibley tells the tale of Alexander Wilson - the most famous 19th-century US bird illustrator after James John Audubon - who captured an ivory bill and took it back to his room, so he could paint it.

"He tied the bird to a table leg, and went out to dinner. When he returned the ivory bill had chiselled its way through the table leg and had almost chiselled its way through the hotel wall and escaped."

The bird went into steep decline from the 1870s, when much of the primeval southern forest that stretched from the Atlantic to the Mississippi was clear-cut. The bird was placed on the Endangered Species List in 1967, when the only evidence that it survived was a possible call heard in East Texas.

"As the forest went, so went the bird," says Luneau. "It's an indicator species, representative of what we did to the forests. Having it return is perhaps a sign that the forests and habitat are coming back as well."

Today, Cornell has hit the Big Woods, which covers 222,500ha, fielding 22 full-time biologists and 112 volunteers around a forested and flooded area the size of Rhode Island, searching for just two woodpeckers.

"It's the biggest search in history for the ivory bill," Rohrbaugh says. A bit like looking for a needle in a haystack? "Yes. But the needle flies."

"We don't look for the bird itself so much," explains Martjan Lannertink, a research biologist. "It has a wide range and the chances of a person and a bird being in the same place are astronomically small." The video, he says, was a "planned fluke".

Instead, searchers are looking for feeding signs - identified by the ivory bill's habit of tearing away bark - or, best of all, roosting sites. This means eyeballing every tree suitable for roosting, plus dying wood that might provide woodpecker grub.

If they find a roost site the project will change from a search to a research mode. "It's the breakthrough we're working towards," says Lannertink, who is convinced the bird exists.

Sibley would like to agree. "This was definitely one of the hardest things I've done," he says of the Science paper. At first he kept his doubts to himself, then shared them with other sceptics and spoke privately to people at Cornell. "I didn't want to do this. I wish the bird in the video was an ivory-billed woodpecker. But the truth is more important."

Meanwhile, as the Big Wood steams up, the mosquitoes swarm, and water moccasins slither through the swamps, the hunting season is drawing to an end. Despite his doubts, Sibley, like every other birder, hopes solid proof will emerge that this charismatic bird survives.

"The ivory bill will most likely be found by an amateur, searching in some out-of-the-way place," he muses. With birding emerging as one of America's fastest-growing leisure pursuits, who knows? Knock on wood.