[CTRL] The Sixth Extinction

[William Shannon]

http://www.nationalgeographic.com/ngm/9902/fngm/index.html



The Sixth Extinction

Text by 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