Is it possible to revive extinct animals? Technology has the answer…

Crispin Andrews

It went from the most abundant bird in the world to extinction within decades. But could modern technology resurrect the passenger pigeon?

The extinction of the passenger pigeon

There were so many birds that they blotted out the midday sun. A mile wide and 300 miles long, the flock took 14 hours to pass overhead. Some roosting sites went on for 40 miles. There were sometimes 100 nests per tree. Writers of the time called them “a living torrent”, “a feathered tempest”, and “a biological storm”. Only the Rocky Mountain locust gathered in greater numbers.

When the first Europeans arrived, North America had five billion passenger pigeons. In 1866, the Ontario flock alone was said to contain three and a half billion birds. Yet on September 1, 1914, the last passenger pigeon, called Martha in honour of President George Washington’s wife, died in Cincinnati Zoo—thousands of years of evolution destroyed in a few decades.

Fast forward 100 years, however, and we find that scientists are making serious attempts to bring back the doomed bird.

 

Is it possible to bring back extinct animals? 

The Passenger Pigeon: Once an Abundant Bird

On March 15 last year, a group of leading scientists, conservationists and researchers came to a conference in Washington—christened Revive and Restore after the organising non-profit group who set it up—to discuss whether humans, responsible for wiping out so many animals, should take advantage of modern technology and make efforts to revive them. This would include not only passenger pigeons but also thylacines, dodos, Steller’s sea cows, moas and woolly mammoths.

At the conference, several scientists, revealed that they’d been trying independently to revive extinct species for a while—such as the Australian gastric-brooding frog, which gave birth through its mouth, and the auroch, an extinct cow that used to roam the plains of Europe and Central Asia. It was also announced that scientists had been sequencing passenger-pigeon DNA since 2001.

Ben Novak, a geneticist working for Revive and Restore on the passenger-pigeon project, explains that DNA from a stuffed specimen is required to bring back an extinct animal. This isn’t a problem with the passenger pigeon; there are 1,532 stuffed specimens in museums and private collections around the world. Joel Greenburg, author of A Feathered River Across the Sky: The Passenger Pigeon’s Flight to Extinction, has a bird called Heinrich—named after German-American composer Anthony Phillip Heinrich, who wrote a whole symphony in 1858 about passenger-pigeon migration while Martha herself was frozen in a 300-pound ice cube when she died.

Unfortunately, DNA from an animal that died over a 100 years ago isn’t well-preserved enough to get the intact genome—just tiny fragments. It’s not like cloning Dolly the sheep from a live animal; DNA starts decaying as soon as an
organism dies.

“Even if you had a two-year-old taxidermy piece, you wouldn’t get whole strands of DNA,” says Novak. “You have to put together enough fragments from a specimen’s damaged cells to get as much of the genome as you can. It’s like tearing up ten copies of a book and then trying to make one book from all the fragments.”

Scientists also need a living animal’s genome to map their copy against—something similar with a high proportion of identical DNA, so they have a picture in front of them of the sort of thing they’re trying to build. Novak is using the passenger pigeon’s closest living relative, the band-tailed pigeon. “It’s virtually the same bird, except passengers had a longer tail, a peach-coloured breast and a stronger flocking mentality,” he says.

Novak thinks it will be at least ten to 15 years before the first passenger pigeon hatches—maybe less, depending on how much funding Revive and Restore can attract. To get there will require further breakthroughs in genome sequencing, and someone also needs to come up with a way of culturing a band-tailed pigeon’s germ cells. Then Novak can start thinking about altering the pigeon’s genetic code and eventually introducing living cells into a band-tailed pigeon embryo.

After that, it’ll be another ten to 15 years to build up a captive flock ready for release, and another 75 years before we see large flocks of pigeons in the skies again.

Find out which extinct animals we'd like to revive

Why the passenger pigeon ruled the roost

Reviving the Passenger Pigeon

Alone, the passenger pigeon was unremarkable; in flocks, it was like no bird we know today. Gigantic hordes of these birds travelled across North America, east of the Rocky Mountains, roosting and nesting in the vast deciduous forests.

For tens of thousands of years, the sheer size of these flocks protected the species from predators. Everything from mink, martens and weasels to hawks, eagles, wolves and bobcats would turn up at passenger-pigeon nesting grounds. Native Americans killed adult birds for food and baby birds for their oil, which they used like butter. But despite all the unwanted attention, nesting colonies were so big they still had a 90 per cent success rate and the species continued to thrive. Unfortunately, against European settlers with their guns and nets, a large flock simply meant a bigger target.

Early settlers caught passenger pigeons for food and feathers, and shot them as vermin. Their descendants shot the birds for sport and cleared forests, the pigeon’s habitat, for farming and wood. But it wasn’t until the mid-19th century, when railroads connected the east-coast cities with the inland settlements, that passenger pigeons became really big business.

“The cheapest protein around, locals called it,” says Greenburg. Hunters shot them out of the sky daily in their thousands—the birds flew so closely together that a single shot could kill a hundred. They were also shot from their nests or shaken out of the trees like leaves. Sometimes the trees were set on fire, or sulphur was burned underneath. Other hunters placed bait on the ground and threw huge nets, some large enough to trap 3,500 birds at a time, over those that landed.

Railroads transported the meat, preserved in ice, to big city markets. Some people even used new telecommunications technology to locate and track the pigeons. Every day, hundreds of hunters harvested thousands of birds. It’s no surprise that, before long, there were no birds left to harvest.

Greenburg says that the Americans started their environmental movement in the 1890s as a direct result of this catastrophe, and the same sense of collective guilt is behind the drive to bring the pigeon back.

 

Moral outrage?

Should we revive the passenger pigeon?

Despite all this, Many of today’s conservationists have concerns about the resources devoted to resurrecting extinct animals. Why should we bother, they argue, when there are so many living animals that desperately need our help to prevent them going the same way? And wouldn’t reintroduced animals face the same problems—such as habitat destruction, poaching and climate change—that wiped them out in the first place?

Even if scientists manage to produce some pigeons—or thylacines or mammoths, for that matter—would there be enough genetic diversity in the captive population to maintain a wild population? Would the cloned animals survive? A Pyrenean ibex, cloned in 2009 from an animal that had died nine years earlier, lived only a few moments. And if a genetically engineered animal does survive, will it be able to function, never mind function like the extinct animal? Will we have a passenger pigeon, or just a band-tailed pigeon that looks a bit like a passenger pigeon?

Ben Novak insists that it’ll be as if the last remaining passenger pigeon hybridised with band-tailed pigeons and the resulting offspring never again bred with band-tailed pigeons. “By our intent, they’ll look like passenger pigeons, flock like passenger pigeons, live as passenger pigeons, and their DNA will have passenger-pigeon genes,” he says.

Novak adds that it’s not mankind’s collective guilt that drives him to do this. It’s simply that there’s an ecological niche for an arboreal pigeon
in the Eastern US, and reinstalling the passenger pigeon would benefit the ecosystem. “Neither band-tailed pigeons nor rock pigeons have filled the ecological niche left by the passenger’s demise,” he says.

Joel Greenburg sees another long-term problem. “People in the US and Canada today won’t tolerate gigantic flocks of birds,” he says. But Novak is unyielding. “If we can’t have million-strong flocks, let’s have tens of thousands.”

 

The lesson of humanity

The thylacine, a wolf-like marsupial from Tasmania.

The Thylacine, a wolf-like marsupial from Tasmania, was killed off by settlers around the same time as the passenger pigeon.

Of course, there are deeper lessons to be learned from the passenger pigeon’s demise, such as what it tells us about human capacity for greed and denial.

“There were so many pigeons—people back then thought it was an endless resource,” says Greenburg. “When, at the height of the slaughter, pigeon numbers started getting lower, people just made up stories to convince themselves that everything was fine, rather than accept the truth.”

Some claimed, for instance, that pigeons nested 11 times a year, when in fact it was only once. Others speculated the birds had flown off to the Arizona Desert, the South American rain-forest, even through the Bermuda triangle.

Greenburg adds that the passenger pigeon is a cautionary tale for those who focus only on what they want today.

“If we’re not good stewards, then even the most abundant resource—fish stocks, oil, water—will eventually run out,” he warns.