Scientists in the US are arguing over the identity of a bird filmed in 2004 which was heralded as the long-extinct ivory-billed woodpecker.
Researchers in Massachusetts said the interpretation of several of the bird's features was "mistaken".
However, experts at Cornell University, who identified the bird two years ago, have dismissed the new claims.
The discovery in Arkansas' Big Woods stunned ornithologists worldwide, with some comparing it to finding the dodo.
The find also ignited hope that other "extinct" birds may be clinging on to survival in isolated places.
'Kick in the stomach'
David Sibley, head of the research group in Massachusetts, said he had analysed the video, audio tapes and other sighting reports and concluded the evidence was not sufficient to prove the bird was an ivory-billed woodpecker.
Mr Sibley, a bird illustrator, said the bird's posture had been interpreted wrongly and that it was more probably a common pileated woodpecker.
He said his findings were like "a kick in the stomach".
However, John Fitzpatrick, of the Cornell Laboratory of Ornithology, said data on the bird's wingspan and flight characteristics point to it being an ivory-billed woodpecker.
He said his critics were using inaccurate models of take-off and flight behaviour and were mistaking "video artefacts" as feather patterns.
Public interest
Ornithologists in California also questioned the identification of the bird last year, prompting the Cornell University researchers to provide audio tapes of the bird's call.
The recordings included the unusual double-rap sounds that ivory-bills produce as well as distinctive nasal sounds they have been known to make.
Whatever the outcome of the row, the search for the woodpecker has boosted tourism in Arkansas by 30% - a woodpecker celebration day was even held in February.
And despite their conflicting interpretations of the video, all the researchers involved in the debate agree on the need to continue conservation efforts that would benefit the ivory-billed woodpecker.
Among the world's largest woodpeckers, the ivory-bill is one of six North American bird species suspected or known to have gone extinct since 1880.
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