Environment & Forests

The SIXTH Extinction

Virginia Morell

The first orange rays of the sun are just beginning to touch the saw grass prairie of Everglades National Park in Florida when our helicopter pilot lifts off from a small airport nearby. He turns low over the park, skimming above the gray-green grasses and morning mist. Here and there small stands of pencil-thin native slash pine show dark green against the pale grasslands. But it’s the open marshy prairie that we seek, home to the endangered Cape Sable seaside sparrow. Heading south, the pilot searches for a particular point on a transect map, then banks and flies due west. Twenty minutes later we’re on the ground. “Here’s your first spot,” he says over the radio to Stuart Pimm, the conservation biologist seated beside me in the back. In front another biologist, Sonny Bass, gives us the thumbs-up sign. Pimm and I, dressed in olive green flight suits and white helmets, jump into the wet marsh and run a short way from the helicopter.

For a moment this seems almost like a scene from Apocalypse Now. The helicopter’s blades whip the air, bending the grasses in a wide swath all around and obliterating every sound except the wap-wap-wap of its rotors. As it peels away, ferrying Bass to the next site a kilometer away, Pimm removes his helmet and turns to me. “Welcome,” he says, his voice rising above the fading roar of the helicopter, “to the front lines of saving biodiversity.”

An avuncular researcher from the University of Tennessee, Pimm is not merely being theatrical. Based on his and his colleagues’ calculations, some 50 percent of the world’s flora and fauna could be on a path to extinction within a hundred years. And everything is affected: fish, birds, insects, plants, and mammals. By Pimm’s count 11 percent of birds, or 1,100 species out of the world’s nearly 10,000, are on the edge of extinction; it’s doubtful that the majority of these 1,100 will live much beyond the end of the next century. The picture is not pretty for plants either. A team of respected botanists recently reported that one in eight plants is at risk of becoming extinct. “It’s not just species on islands or in rain forests or just birds or big charismatic mammals,” says Pimm. “It’s everything and it’s everywhere. It’s here in this national park. It is a worldwide epidemic of extinctions.”

Such a rate of extinction has occurred only five times since complex life emerged, and each time it was caused by a catastrophic natural disaster. For instance, geologists have found evidence that a meteorite crashed into Earth 65 million years ago, leading to the demise of the dinosaurs. That was the most recent major extinction. Today the Earth is again in extinction’s grip—but the cause has changed. The sixth extinction is not happening because of some external force. It is happening because of us, Homo sapiens, an “exterminator species,” as one scientist has characterized humankind. The collective actions of humans—developing and paving over the landscape, clear-cutting forests, polluting rivers and streams, altering the atmosphere’s protective ozone layer, and populating nearly every place imaginable—are bringing an end to the lives of creatures across the Earth. “I think we must ask ourselves if this is really what we want to do to God’s creation,” says Pimm. “To drive it to extinction? Because extinction really is irreversible; species that go extinct are lost forever. This is not like Jurassic Park. We can’t bring them back.”

In Pimm’s eyes people should be stewards of their neighboring species. That’s why he’s here at dawn in the Everglades, fighting to save the life of a little brown-and-white songbird with a smattering of gold feathers above its eyes.

Found only in this park, Big Cypress National Preserve, and nearby areas, the Cape Sable sparrow was once fairly common in the Everglades’ hundred square miles [160.9 square kilometers] of prairie lands, which lie adjacent to its better known “river of grass.” In 1992 the sparrow’s population registered a healthy 6,400 individuals. By 1995 the sparrow’s numbers had taken a nosedive: Its population dropped by 60 percent to 2,600. “It was clearly on its way out,” says Pimm, turning to set his helmet on the ground. “And to me that was unconscionable. In a national park of this size [the Everglades encompasses 1.5 million acres] (.6075 million hectares) and in the richest country in the world, species shouldn’t be going extinct because of our actions. These areas, after all, were set up for their protection.”

Raising his binoculars, Pimm surveys the surrounding grasses, then cups his ear to listen for the sparrow’s call. “Ahhh, there’s one. Do you hear it? Listen for a chit-chit-tweeeee,” he says, imitating the bird’s short, quick notes and insect-like buzz. We stand silently, and a few moments later the call comes again, clear and brazen in the still morning air. “That’s the male defending his territory; the birds have just started nesting, and so this is the best time to get a count of their population.” Through our binoculars we spot this throaty male, perched at the end of a swaying grass stalk, his beak open, singing to the sky.

Throughout the three-month nesting period Pimm and Bass make these counts, flying a different line of their transect map each dawn and stopping at sites spaced precisely a kilometer (0.6 mile) apart to look and listen for the birds. The resulting data give them not only a count of the number of eligible males but also a map of where the birds prefer to build their nests. And that, in turn, has revealed what is harming them: Too much water. “The birds start nesting in the middle of April,” Pimm says. “They weave the grasses together to form a bowl about three inches [76.2 millimeters] off the ground.”

Because they nest so close to the ground, there can’t be any standing water if they’re to raise a brood successfully. But water throughout and around the Everglades is managed and controlled by two agencies, the South Florida Water Management District and the Army Corps of Engineers. Water, which naturally would have flowed throughout the park, is held in reservoirs, channeled in dikes, and, above all, prevented from spilling into bordering farms and the suburbs of Greater Miami. To water managers, say Pimm and Bass, the drying western prairies of the Everglades in the spring look like an excellent place to dump excess water, which is what happened for several years beginning in 1993. While this protected some homes and roads, it has proved a disaster for the sparrow and, the biologists suspect, for other species, including many wading birds, such as egrets and herons whose nesting patterns have also been disrupted. “We’re losing the sparrow and probably other species just because of water management decisions,” says Bass on the flight back to the airport.

“Admittedly, it is a big problem managing the water here, especially in stormy years. But all it takes is holding off a couple of months, as the agencies did last year, to let the birds nest and rear their young. It’s a matter of making the right decision.”

If the Cape Sable sparrow’s nesting grounds are not flooded, Pimm and Bass think their population will begin to increase.

For other species, though, no decision will change their fate; they are simply doomed to disappear from Earth.

In London, at the Royal Botanic Gardens at Kew, two horticulturists lead the way through a greenhouse, stopping to point out plants, from shrubs to spindly trees, that no longer exist in the wild. Kew researchers hope eventually to return some to their homelands. But for others the greenhouse is the end of the line.

“Now that poor thing, an Encephalartos woodii, hasn’t had sex in about a hundred years,” says Stefan Czeladzinski, a horticulturist-in-training, referring to one of the trees. “It’s one of our living dead.” The plant, about five feet [1.5 meters] tall with leathery leaves, is from Natal in South Africa. It is a dioecious species, meaning that its individuals are either male or female. In this case the plant is a male, and no females are known to exist. “Botanists have combed Natal looking for one, but they’ve never found it,” says Czeladzinski. This survivor comes from cuttings from the last wild plant, which was moved to a botanical garden decades ago. All E. woodii plants alive today, including the lonely Kew specimen, are clones of that wild male; they are genetically identical and will never reproduce naturally unless a female is found.

And it’s not just the Encephalartos that has been lost. Most of the native flora of many islands is extinct, beaten out by species that settlers introduced from Europe more than 300 years ago. “In some islands the habitats were already destroyed by the time the first botanists arrived,” says Michael Maunder, a tall, dark-haired conservation biologist at Kew who specializes in the recovery of critically endangered plants. “We’ve managed to piece the flora together by reading travelers’ diaries, collecting pollen from soil samples, and having bits of wood identified. But we only have a shadow of an idea of what was once there.”

Because the species on islands are often endemics—meaning that they are found nowhere else in the world—their populations are typically small and consequently more prone to extinction. When a foreign plant is introduced—for example, the Chinese guava tree that blankets much of Mauritius, an island off Madagascar—it can become a weed that ends all others.

Kew Gardens and the Mauritian Wildlife Foundation have launched a project basically to weed the island of Mauritius. On the wall of his office Maunder has a large photo of an area known as the Black River Gorge, which retains remnants of Mauritius’s original forest. These plots, some a mere acre[0.41 hectare] in size, are caged in chain-link fences to keep out the deer and pigs, also introduced from Europe. Outside, as if biding its time, grows a thick, tangled mat of similarly introduced guava and privet.

“The plots are weeded every year,” Maunder says. “We can keep these small plots of natives going, but how do we extend them? Can we ever fully restore Mauritius?” Maunder only shakes his head.

Throughout the islands of the Indian Ocean and the South Pacific, the tale is much the same: extinctions being driven by species introduced by European explorers a few hundred years ago. But there was an even earlier round of extinctions in these and other places as humans moved out of Africa and into new lands. In Australia the arrival of the first people 50,000 to 60,000 years ago may have led to the demise of that island continent’s megafauna, which included 20 species of giant kangaroos, the marsupial lion, and diprotodons—herbivorous marsupials that resembled cow-size rodents.

“I’ve no doubt that people hunted them to extinction,” says Tim Flannery, a mammalogist at the Australian Museum in Sydney, who has investigated his country’s extinctions, past and present. “It’s the same story in New Guinea and New Zealand. There you can still find some of the evidence, such as piles of bones from the giant moas [large, flightless birds] that the Maori killed until there were no more.”

“The same thing happened here,” says Dolores Piperno, an archaeologist at the Smithsonian Tropical Research Institute in Panama, giving a quick smile and a sigh almost simultaneously. “Let me show you something.” She walks briskly across the tile floor of her office and riffles through a row of files. From one she pulls out a large chart and unfolds it on her desk. It’s a graph of plant fossils collected from sediments taken from a lake in central Panama, and it spans a period from 14,000 years ago to the present.

Fourteen thousand years ago the diversity of trees and plants was relatively modest, reflecting the tail end of the last ice age in the tropics. But by 11,000 years ago, as Panama began to warm up, the variety of flora increased dramatically. Piperno traces this burst of plant life with her forefinger as the graph makes an upward spike, but then the line takes a sudden downward plunge, as if tracking the collapse of the stock market in 1929. “That,” she says, tapping the graph, “is when people began practicing slash-and-burn agriculture here, about 7,000 years ago. That’s what people can do to a forest with a stone ax and fire. It shows that the idea of the noble savage—that people in the past in simpler societies lived in harmony with the natural world—isn’t true. We humans have short-term goals. That’s what makes saving species and conserving the environment for the long term so hard. We want results now.”

But that short-term outlook can also work against people by eliminating potentially useful species. “We have not yet identified all the plants on Earth,” says Sir Ghillean Prance, the director of Kew Gardens, “and we’re losing them, I’m afraid, faster than we can catalog them.” Because so many of our most effective medicines, from aspirin to morphine, come from plants, Prance worries that in losing the flora of the world, we’re also losing the possibility of finding new drugs and chemicals.

“Every time we lose a species, we lose an option for the future,” he says. “We lose a potential cure for AIDS or a virus-resistant crop. So we must somehow stop losing species, not just for the sake of our planet but for our own selfish needs and uses.” The Cape Sable sparrow, of course, is not likely to lead to a cure for cancer or to any other earthshaking discovery. Nor are most species around us. What would it matter if this little bird, or any of the 1,100 others on Pimm’s list, becomes extinct? That thought crosses my mind one morning while joining his team of bird banders in the Everglades.

To trap the sparrows, the team watches the males to identify each individual’s nesting territory. The banders then set up a mist net nearby and play a tape recording of another male’s song, fooling the resident male into thinking a rival has arrived to court his mate. That kind of cheeky behavior elicits an immediate response from the male in this territory. He swoops in low over the grass, stops for a few seconds atop a single blade to sing his own territorial song, and then flies determinedly into the net, where he thinks his competitor is lurking.

Two banders rush forward to catch him. They weigh and measure him and gently fasten two yellow bands onto his left leg. “Would you like to let him go?” asks Dave Okines, the chief bander. He shows me how to hold the sparrow’s legs between my first and second fingers, so that he sits upright on the top of my hand. For a brief moment, I keep him there, feeling his warmth, admiring the bright gold of his eyebrow feathers. Then I open my hand and he’s gone in a flash, and I allow myself the thought that the sixth extinction is not inevitable. If humans are the cause, they can also be the solution.

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