The ivory-billed woodpecker, a spectacular bird long thought to be extinct, has been found alive in North America, Science magazine reports.
The broad bill continues to grow throughout its life and is worn down by hard pounding on trees
The news has stunned ornithologists worldwide, with some comparing the discovery to finding the dodo.
Researchers began an intense year-long search after a tip-off before finally capturing the bird on video.
The find has ignited hope that other "extinct" birds may be clinging on to survival in isolated places.
"This find is so significant that it is really difficult to describe," Alistair Gammell, of the UK's Royal Society for the Protection of Birds (RSPB), told BBC News. "We sadly won't rediscover the dodo, but it is almost on that level."
Frank Gill, of the US National Audubon Society, added: "This is huge, just huge. It is kind of like finding Elvis."
The "stunning" red, white and black woodpecker was formerly distributed across the south-eastern United States and Cuba.
The bird carves out a narrow niche for itself by drilling in mature trees, and logging and forest clearance for agriculture began to impinge on its environment.
By the 1920s, it was assumed to be extinct, although, in 1944, there was one more confirmed sighting in North America of a lonely unpaired female, above the remnants of an over-cut forest.
Since then, decades of searches yielded nothing and hope gradually faded away.
Now, finally, the bird has been seen again in the Big Woods of eastern Arkansas.
The discovery was first made on 11 February 2004, by Gene Sparling, of Hot Springs, Arkansas, who was kayaking in a reserve in Big Woods. He saw an unusually large red-crested woodpecker fly towards him and land on a nearby tree.
He said the creature did not look quite like anything he had seen before, so he contacted Cornell University's Living Bird magazine.
After a team of experts interviewed him, they felt they might be onto something special.
A second chance
John Fitzpatrick, of Cornell University, headed the search party, which included Tim Gallagher, editor of Living Bird.
Within a month, Dr Gallagher had seen the ivory-billed woodpecker for himself.
Describing the moment he first set eyes on it, he said: "Just to think this bird made it into the 21st Century gives me chills.
"It's like a funeral shroud has been pulled back, giving us a glimpse of a living bird, rising Lazarus-like from the grave."
The last confirmed sightings were in the '30s and '40s
The team finally went on to capture the bird on video, which allowed them to confirm its identity.
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.
"This provides hope for [other] species classified as potentially extinct," said Stuart Butchart, of BirdLife International.
It also offers an extra incentive to protect the habitat of the ivory-bill, as well as other birds.
"Amazingly America may have another chance to protect the future of this spectacular bird and the awesome forests in which it lives," Mr Fitzpatrick said.
"It is the most beautiful bird we could imagine rediscovering. It is a magical bird.
"For those of us who tenaciously cling to the idea that man can live alongside fellow species, this is the most incredible ray of hope."