Less than 200 years ago, passenger pigeons were the No. 1 bird in North America, and possibly on Earth. They numbered around 5 billion at their peak, forming huge flocks that stretched up to a mile wide and 300 miles long. They could block the sun for days at a time as they thundered overhead.

"The pigeon was a biological storm," conservationist Aldo Leopold once wrote. "He was the lightning that played between two opposing potentials of intolerable intensity: the fat of the land and the oxygen of the air. Yearly the feathered tempest roared up, down, and across the continent, sucking up the laden fruits of forest and prairie, burning them in a traveling blast of life."

And then, within a few decades, it all came crashing down. One of the planet's most successful birds went from billions to one, dwindling down to a final survivor named Martha who lived her entire life in captivity. She was found dead in her cage at the Cincinnati Zoo around 1 p.m. on Sept. 1, 1914, completing one of the fastest and most dramatic extinctions ever witnessed by humans.

We weren't exactly bystanders, of course. People hunted passenger pigeons to extinction, based on the fallacy that nothing of such abundance could be wiped out by human hands. And now, as we reach the 100th anniversary of being proven wrong about that, Martha has become more than just the last of her species — she's a symbolic reminder not to make the same mistakes again.

"It's a powerful cautionary tale that no matter how abundant something is — it could be water, fuel or something alive — if we're not good stewards we can lose it," says naturalist Joel Greenberg, author of "A Feathered River Across the Sky: The Passenger Pigeon's Flight to Extinction," which was published earlier this year. "And if something as abundant as the passenger pigeon can disappear in just a few decades, something rarer could disappear in an instant."

beech forest

Beech forests, like this one in Wisconsin, were a popular hangout for passenger pigeons. (Photo: Joshua Mayer/Flickr)

Birds of a feather

A lone passenger pigeon might have looked unremarkable — sort of like a larger, more colorful mourning dove — but their flocks were legendary. "The air was literally filled with pigeons," John James Audubon wrote in 1813, describing a flight he encountered in Kentucky. "The light of noon-day was obscured as by an eclipse, the dung fell in spots, not unlike melting flakes of snow; and the continued buzz of the wings had a tendency to lull my senses to repose."

Many descriptions of passenger pigeons would seem dubious if they weren't so plentiful and consistent. "People wrote over 300 years in five or six languages describing these birds darkening the skies over major cities of the Eastern U.S. and Canada," Greenberg tells MNN. The flocks would fill forests as they devoured acorns and beechnuts, helping spread white oaks and beech trees while providing a feast for predators like bobcats, eagles, foxes, hawks, minks, owls and wolves.

That's a tactic known as "predator satiation," similar to what cicadas do. By periodically flooding a habitat with pigeons, the species could sustainably satisfy its predators. All but one predator, that is.

A trailer for the 2014 documentary "From Billions to None," which details the story of passenger pigeons' extinction.

A bird in hand

Humans hunted passenger pigeons for food and feathers long before Europeans came to North America, but something changed in the 1800s. Technology turned the hunts into an industrial slaughter, with pigeoners using the telegraph to track flocks and the railroad to move their spoils.

People used all kinds of maniacal tactics to kill pigeons, including burning down nest trees, baiting the birds with alcohol-soaked grain, trapping them in huge nets and even luring them with captive pigeons on small perches — the origin of the term "stool pigeon." On top of that, loggers had shrunk and fragmented swaths of old-growth forest by the 1880s, providing pigeons with fewer places to flee.

And when pigeon populations began to plummet, the hunters doubled down.

"There were 600 to 3,000 professional hunters who did nothing but chase the birds all year long," Greenberg says. "The people hunting them knew they were decreasing, but instead of saying 'let's hold off,' they hunted them more intensely. Toward the end, they just started raiding all the nests. They wanted to get every last bird, squeeze every last penny out of them before they were gone."

As with many of today's environmental issues, there was also an effort to obscure the missing pigeons. "People were making things up to allay concerns that the birds were decreasing," Greenberg adds. "They would say things like the birds lay eggs all year long, even though they just laid an egg once per year. Or they would say the birds moved to South America and changed their appearance."

For anyone who had seen torrents of passenger pigeons in the 1860s and 1870s, it was hard to believe they were nearly extinct in the 1890s. After the final holdouts in Michigan vanished, many people assumed the birds moved farther west, maybe to Arizona or Puget Sound. Henry Ford even suggested the entire species had made a break for Asia. Eventually, though, denial gave way to grim acceptance. The last-known wild passenger pigeon was shot April 3, 1902, in Laurel, Indiana.

passenger pigeons

Captive passenger pigeons perch at a Chicago aviary in 1896. (Photo: Wikimedia Commons)

Martha's swan song

Three captive flocks of passenger pigeons made it into the 1900s, but cages were poor substitutes for forests that once hosted up to 100 nests per tree. Without their natural population density — or modern captive-breeding standards — these highly social birds didn't stand a chance. Two captive flocks in Milwaukee and Chicago were dead by 1908, leaving just Martha and two males at the Cincinnati Zoo. After those males died in 1909 and 1910, Martha was the "endling" of her species.

MarthaNamed after first lady Martha Washington, Martha (pictured) was born in captivity and spent her life in cages. She was a celebrity by the time she died, reportedly at age 29. She had suffered an apoplectic stroke several weeks earlier, requiring the zoo to build a lower perch since she was too weak to reach her old one.

Martha's body was immediately frozen in a 300-pound block of ice and shipped by train to the Smithsonian Institution in Washington, where she was preserved as a taxidermy mount and anatomical specimen. You can now see a 360-degree view of her as part of the Smithsonian's "Once There Were Billions" exhibit on extinct North American birds, which runs through October 2015.

"In the case of the passenger pigeon, it was so clear Martha was the last of her species," says Todd McGrain, a Cornell University art professor and co-creator of the Lost Bird Project, which honors extinct birds with memorial statues. "It's rare for a species to go extinct like that, out in public view."

Life after extinction

Even rarer than watching a species go extinct, however, is watching one come back. And thanks to a "Jurassic Park"-esque effort known as Revive & Restore, supported by the San Francisco-based Long Now Foundation, that might actually happen one day for the passenger pigeon.

Revive & Restore isn't quite "Jurassic Park," though, and not just because it can't bring back a T-rex. Its goal is to revive more recently extinct species, and to return them to the wild rather than hoarding them in a theme park. In hopes of kicking off the de-extinction era with a crowd favorite, its flagship project is The Great Passenger Pigeon Comeback, which aims to produce live passenger pigeons using their sequenced genome along with that of the related band-tailed pigeon.

band-tailed pigeon

Band-tailed pigeons, which inhabit western North America, are the passenger pigeon's closest living relatives. (Photo: Shutterstock)

"De-extinction is not a 'quick fix' science," Long Now co-founder Stewart Brand writes on the group's website. "Passenger pigeons, for example, will initially be bred in captivity by zoos, then placed into netted woods, and then finally re-introduced to portions of their original habitat — America's eastern deciduous forest. Before that happens, the U.S. Fish and Wildlife Service and regulatory agencies in the relevant states will have to agree to welcome the resurgent birds."

The idea is intriguing, but many conservationists and bird enthusiasts are skeptical. It would need to produce another captive-breeding program, for example, which can be difficult and expensive even under normal circumstances. Passenger pigeons' habitats have also been transformed since they last saw them, raising questions about their viability in the wild (although a recent study does suggest they could survive in smaller flocks). And more broadly, critics say the allure of de-extinction might soften our respect for the finality of extinction, making wildlife conservation seem less urgent.

"I completely understand the motivation," says McGrain, whose passenger pigeon sculpture (pictured) is part of the Once There Were Billions exhibit at the Smithsonian Gardens. "I'm fascinated by the passenger pigeon, and have been since I was a kid. I dream about what it must have been like to see those flocks. But I have real problems with that as a focused initiative."

Greenberg is cautious, too, pointing out that rewilded passenger pigeons could be mistaken for mourning doves, which are legally hunted in the U.S. And even if they thrive, he adds, there will inevitably be friction with people. "We live in an age when golfers get upset if a goose poops on their shoe," he says. "And there are descriptions of [passenger pigeon] droppings falling like snow. It was a different era back then. Horses were everywhere. I think we just gross out a little more easily now."

Any passenger pigeon revival is decades away, though, giving us time to reflect on the centennial of its extinction without getting ahead of ourselves. Maybe we will bring the species back, but that won't do much good if we still haven't learned our lesson from losing it.

Earth is now on the cusp of a mass extinction event, which has happened five times before but never in human history — and never with human help. The largely man-made crisis may have already raised the natural or "background" extinction rate by a factor of 1,000. Iconic animals such as tigers, sharks, gorillas and elephants could follow Martha if more isn't done to protect them.

"Forgetting is the first step to completely removing something from our cultural collective memory," McGrain says. "A society that remembers is a healthier society than one that keeps restarting from scratch. We applied a great deal of our modern ingenuity to harvest those birds, and we did it without reflecting on the effect it would have on the birds or on the broader ecosystem. I think there's a great lesson in that about where we need to apply our creativity and our technology."

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