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Pictured is Martha - the last remaining passenger pigeon - who died in 1914, marking the rapid extinction of a bird species due to human activity

In 1866, a billion-strong flock of passenger pigeons, 300 miles long and one mile wide, darkened the skies of Ontario for 14 hours as they flew overhead.

But less 50 years later, these impressive creatures, once abundant in North America, became extinct as a result of cutting down forests and hunting by humans.

Now geneticists in San Francisco are hoping to bring the passenger pigeon back to life using centuries-old DNA.

The company, Revive and Restore, will use a process known as 'de-extinction' which, if successful, could also be used to bring back hundreds of other extinct species.

The process involves using passenger pigeon DNA taken from museum specimens. Scientists can then fill in the blanks with fragments from the band-tailed pigeon.

This reconstructed genome would be placed into stem cells of a band-tailed pigeon, which would transform into a cell that could become a sperm or an egg.

The scientists would then inject these so-called germ cells into band-tailed pigeons.

Their hope is that, as those birds mate, their chicks would have some passenger pigeon genes.

'The genomes of the two birds will be compared in close detail, to determine which differences are most crucial,' the company said on their website.

'The data and analysis will begin with the process of converting viable band-tailed DNA into viable passenger pigeon DNA.'

The process involves using passenger pigeon DNA taken from museum specimens. Scientists will then fill in the blanks with fragments of DNA from the band-tailed pigeon.This reconstructed genome would be placed into stem cells of a band-tailed pigeon. The scientists would then inject these so-called germ cells into band-tailed pigeons. Their hope is that, as those birds mate, their chicks would have some passenger pigeon genes

A century ago, Martha, a red-eyed, grey and brown bird famous as the last surviving passenger pigeon, keeled over, marking an extinction of a species.

Revive and Restore will take the long-dead pigeon out of the file cabinets of history as part of their project.

'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 said.

In the 18th and 19th centuries the passenger pigeon was the most abundant bird species on Earth.

Unlike the domesticated carrier pigeon used for messages, these were wild birds. They were easy to catch because they stayed together.

But they were considered a poor man's food; domestic workers complained about eating too much passenger pigeon.

In the 18th and 19th centuries the passenger pigeon was the most abundant bird species on Earth. Unlike the domesticated carrier pigeon used for messages, these were wild birds. They were easy to catch because they stayed together

Band-tailed Pigeon (pictured) could help bring extinct Passenger Pigeon back to life, according to scientists

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

Examination of the passenger pigeon's genetic code shows that their population grew and fell regularly from as much as five billion to as few as tens of millions.

The chief causes of the extinction - cutting down Eastern U.S. forests and hunting - were man-made, Professor Zink added.

By 1900, there were no passenger pigeons left in the wild. By 1914, there was just one - 29-year-old Martha at the Cincinnati Zoo.

Then on September 1, 1914, Martha was found lying on the bottom of her cage. The passenger pigeon was now extinct.

Pictured are stem cells made from the cell nucleas. These will be a crucial part of the 'de-extinction' process

It was the first public extinction, something people used to think happened only to relics of the past like dinosaurs, or critters stuck on islands like dodos, Pimm and other scientists said.

Bringing the passenger pigeon back would cost millions and take at least a decade, said Ben Novak who is leading the project.

Some scientists, however, don't believe the idea is ethical or practical.

But Professor Novak sees a world on the verge of a mass extinction of many species and feels something has to be done about it.

Reviving some long-lost species, he said, may offer 'a type of justice for what we're doing now and also teach people it's so much easier to keep something alive than to bring it back to life.'

MARTHA: THE LAST REMAINING PASSENGER PIGEON 

On September 1, 1914, Martha  - the last remaining passenger pigeon - (pictured) was found lying on the bottom of her cage

By 1900, there we no passenger pigeons left in the wild. By 1914, there was just 29-year-old Martha at the Cincinnati Zoo. People lined up to see her.

Then on September 1, 1914, Martha was found lying on the bottom of her cage meaning the passenger pigeon had become extinct. It had gone from billions of birds to zero in around a century.

It was the first public extinction, something people used to think happened only to relics of the past like dinosaurs, or animals stuck on islands like dodos.

Martha, the last of her kind, was put in a 300-pound block of ice and shipped to Washington D.C. and the Smithsonian.

She was stuffed and mounted.

When she travelled back to Cincinnati or to San Diego for a big conservation conference, she flew in a first class seat.

For the last 15 years, she has been in a metal filing cabinet in the bowels of the Smithsonian, stuck on the same stick with an older stuffed unrelated pigeon named George.

On Monday, they were separated, George was put back in storage and Martha was ready for a comeback.

An exhibit on her extinction and the 100th anniversary starts June 24 at the Smithsonian.