Nearly a century after it went extinct, the passenger pigeon -- at one time one of the most common birds on Earth, numbering in the billions -- may be coming back, thanks to geneticists and DNA from stuffed birds in museums.

In the 18th and 19th centuries, flocks of billions of passenger pigeons were a common sight, with migrating streams of the birds sometimes darkening the skies overhead for days on end.

Because they stayed together in flocks, the birds were easily caught and killed, and were so plentiful they were regarded as a poor man's food, experts said.

But by the later decades of the 1800s, land clearance for agriculture and overhunting saw the passenger pigeon on an inexorable slide toward extinction.

By 1900 none were left alive in the wild and the last surviving passenger pigeon, dubbed Martha -- named for Martha Washington -- died in 1914 at the Cincinnati Zoo & Botanical Garden.

Her death brought home a sobering fact to the public, that extinction wasn't something that just happened in the distant past to species like dinosaurs.

"Here was a bird like the robin that everybody knew and within a generation or two, it was gone -- and we were its cause," Duke University ecologist Stuart Pimm says.

It was the speed of its extinction -- in evolutionary terms, a blink of an eye -- that was so extraordinary, experts said.

"Nobody ever dreamed that a bird that common could be brought into extinction that quickly," University of Minnesota evolutionary biologist Bob Zink said.

But the passenger pigeon might be resurrected from the dead, other experts say.

Scientists at a San Francisco-based nonprofit dedicated to species "de-extinction" say they will attempt to use genetic engineering techniques to create new, living specimens of the long-extinct bird.

Researchers at Revive & Restore say they've collected DNA samples from passenger pigeons preserved in a number of museums, with the goal of creating live passenger pigeons in a laboratory.

The experiment would breed band-tailed pigeons, a living relative of the extinct pigeon, and then engineer their DNA using the collected passenger pigeon genetic material and transfer it into band-tailed bird's genomes.

The effort is likely to have a price tag in the millions and could take at least 10 years, Revive & Restore researcher Ben Novak acknowledges.

With many species in the world hovering on the edge of extinction, there is reason to attempt bringing back at least this one, he says.

It might offer "a type of justice for what we're doing now" and also teach people about species conservation, he says. "It's so much easier to keep something alive than to bring it back to life."

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