The Best American Science and Nature Writing 2010

by Tim Folger

  The first time I visited, Griffith pointed out various tanks containing frogs that have essentially disappeared from the wild. These include the Panamanian golden frog, which, in addition to its extraordinary coloring, is known for its unusual method of communication; the frogs signal to one another using a kind of sema phore. Griffith said that he expected between a third and a half of all Panama's amphibians to be gone within the next five years. Some species, he said, will probably vanish without anyone's realizing it: "Unfortunately, we are losing all these amphibians before we even know that they exist."

  Griffith still goes out collecting for EVACC. Since there are hardly any frogs to be found around El Valle, he has to travel farther afield, across the Panama Canal, to the eastern half of the country.

  One day this winter, I set out with him on one of his expeditions, along with two American zookeepers who were also visiting EVACC. The four of us spent a night in a town called Cerro Azul and, at dawn the next morning, drove in a truck to the ranger station at the entrance to Chagres National Park. Griffith was hoping to find females of two species that EVACC is short of. He pulled out his collecting permit and presented it to the sleepy officials manning the station. Some underfed dogs came out to sniff around.

  Beyond the ranger station, the road turned into a series of craters connected by ruts. Griffith put Jimi Hendrix on the truck's CD player, and we bounced along to the throbbing beat. (When the driving got particularly gruesome, he would turn down the volume.) Frog collecting requires a lot of supplies, so Griffith had hired two men to help with the carrying. At the very last cluster of houses, in the village of Los Ángeles, they materialized out of the mist. We bounced on until the truck couldn't go any farther; then we all got out and started walking.

  The trail wound its way through the rainforest in a slather of red mud. Every few hundred yards, the main path was crossed by a narrower one; these paths had been made by leaf-cutter ants, making millions—perhaps billions—of trips to bring bits of greenery back to their colonies. (The colonies, which look like mounds of sawdust, can cover an area the size of a suburban back yard.) One of the Americans, Chris Bednarski, from the Houston Zoo, warned me to avoid the soldier ants, which will leave their jaws in your shin even after they're dead. "Those'll really mess you up," he observed. The other American, John Chastain, from the Toledo Zoo, was carrying a long hook, for use against venomous snakes. "Fortunately, the ones that can really mess you up are pretty rare," Bednarski said. Howler monkeys screamed in the distance. Someone pointed out jaguar prints in the soft ground.

  After about five hours, we emerged into a small clearing. While we were setting up camp, a blue morpho butterfly flitted by, its wings the color of the sky.

  That evening, after the sun set, we strapped on headlamps and clambered down to a nearby stream. Many amphibians are nocturnal, and the only way to see them is to go looking in the dark, an exercise that's as tricky as it sounds. I kept slipping and violating Rule No. 1 of rainforest safety: never grab onto something if you don't know what it is. After one of my falls, Bednarski showed me a tarantula the size of my fist that he had found on a nearby tree.

  One technique for finding amphibians at night is to shine a light into the forest and look for the reflecting glow of their eyes. The first amphibian sighted this way was a San José Cochran frog, perched on top of a leaf. San José Cochran frogs are part of a larger family known as "glass frogs," so named because their translucent skin reveals the outlines of their internal organs. This particular glass frog was green with tiny yellow dots. Griffith pulled a pair of surgical gloves out of his pack. He stood entirely still and then, with a heronlike gesture, darted to scoop up the frog. With his free hand, he took what looked like the end of a Q-Tip and swabbed the frog's belly. Finally, he put the Q-Tip in a little plastic vial, placed the frog back on the leaf, and pulled out his camera. The frog stared into the lens impassively.

  We continued to grope through the blackness. Someone spotted a La Loma robber frog, which is an orangey red, like the forest floor; someone else spotted a Warzewitsch frog, which is bright green and shaped like a leaf. With every frog, Griffith went through the same routine—snatching it up, swabbing its belly, photographing it. Finally, we came upon a pair of Panamanian robber frogs locked in amplexus—the amphibian version of sex. Griffith left these two alone.

  One of the frogs that Griffith was hoping to catch, the horned marsupial frog, has a distinctive call that's been likened to the sound of a champagne bottle being uncorked. As we sloshed along, the call seemed to be emanating from several directions at once. Sometimes it sounded as if it were right nearby, but then, as we approached, it would fall silent. Griffith began imitating the call, making a cork-popping sound with his lips. Eventually, he decided that the rest of us were scaring the frogs with our splashing. He waded ahead, while we stood in the middle of the stream, trying not to move. When Griffith gestured us over, we found him standing in front of a large yellow frog with long toes and an owlish face. It was sitting on a tree limb, just above eye level. Griffith grabbed the frog and turned it over. Where a female marsupial frog would have a pouch, this one had none. Griffith swabbed it, photographed it, and put it back in the tree.

  "You are a beautiful boy," he told the frog.

  Amphibians are among the planet's great survivors. The ancestors of today's frogs and toads crawled out of the water some 400 million years ago, and by 250 million years ago the earliest representatives of what became the modern amphibian clades—one includes frogs and toads; a second, newts and salamanders—had evolved. This means that amphibians have been around not just longer than mammals, say, or birds; they have been around since before there were dinosaurs. Most amphibians—the word comes from the Greek meaning "double life"—are still closely tied to the aquatic realm from which they emerged. (The ancient Egyptians thought that frogs were produced by the coupling of land and water during the annual flooding of the Nile.) Their eggs, which have no shells, must be kept moist in order to develop. There are frogs that lay their eggs in streams, frogs that lay them in temporary pools, frogs that lay them underground, and frogs that lay them in nests that they construct out of foam. In addition to frogs that carry their eggs on their backs and in pouches, there are frogs that carry them in their vocal sacs, and, until recently, at least, there were frogs that carried their eggs in their stomachs and gave birth through their mouths. Amphibians emerged at a time when all the land on Earth was part of one large mass; they have since adapted to conditions on every continent except Antarctica. Worldwide, more than 6,000 species have been identified, and while the greatest number are found in the tropical rainforests, there are amphibians that, like the sandhill frog of Australia, can live in the desert and also amphibians that, like the wood frog, can live above the Arctic Circle. Several common North American frogs, including spring peepers, are able to survive the winter frozen solid.

  When, about two decades ago, researchers first noticed that something odd was happening to amphibians, the evidence didn't seem to make sense. David Wake is a biologist at the University of California at Berkeley. In the early 1980s, his students began returning from frog-collecting trips in the Sierra Nevada empty-handed. Wake remembered from his own student days that frogs in the Sierras had been difficult to avoid. "You'd be walking through meadows, and you'd inadvertently step on them," he told me. "They were just everywhere." Wake assumed that his students were going to the wrong spots or that they just didn't know how to look. Then a postdoc with several years of experience collecting amphibians told him that he couldn't find any either. "I said, 'OK, I'll go up with you and we'll go out to some proven places,'" Wake recalled. "And I took him out to this proven place and we found, like, two toads."

  Around the same time, other researchers, in other parts of the world, reported similar difficulties. In the late 1980s, a herpetologist named Marty Crump went to Costa Rica to study golden toads; she was forced to change her project because, from one year to the next, the
toad essentially vanished. (The golden toad, now regarded as extinct, was actually orange; it is not to be confused with the Panamanian golden frog, which is technically also a toad.) Probably simultaneously, in central Costa Rica the populations of twenty species of frogs and toads suddenly crashed. In Ecuador the jambato toad, a familiar visitor to back-yard gardens, disappeared in a matter of years. And in northeastern Australia, biologists noticed that more than a dozen amphibian species, including the southern day frog, one of the more common in the region, were experiencing drastic declines.

  But as the number of examples increased, the evidence only seemed to grow more confounding. Though amphibians in some remote and—relatively speaking—pristine spots seemed to be collapsing, those in other, more obviously disturbed habitats seemed to be doing fine. Meanwhile, in many parts of the world there weren't good data on amphibian populations to begin with, so it was hard to determine what represented terminal descent and what might be just a temporary dip.

  "It was very controversial to say that amphibians were disappearing," Andrew Blaustein, a zoology professor at Oregon State Uni versity, recalls. Blaustein, who was studying the mating behavior of frogs and toads in the Cascade Mountains, had observed that some long-standing populations simply weren't there anymore. "The debate was whether or not there really was an amphibian population problem, because some people were saying it was just natural variation." At the point that Karen Lips went to look for her first research site, she purposefully tried to steer clear of the controversy.

  "I didn't want to work on amphibian decline," she told me. "There were endless debates about whether this was a function of randomness or a true pattern. And the last thing you want to do is get involved when you don't know what's going on."

  But the debate was not to be avoided. Even amphibians that had never seen a pond or a forest started dying. Blue poison-dart frogs, which are native to Suriname, had been raised at the National Zoo, in Washington, D.C., for several generations. Then, suddenly, the zoo's tank-bred frogs were nearly wiped out.

  It is difficult to say when, exactly, the current extinction event—sometimes called the sixth extinction—began. What might be thought of as its opening phase appears to have started about 50,000 years ago. At that time, Australia was home to a fantastic assortment of enormous animals; these included a wombatlike creature the size of a hippo, a land tortoise nearly as big as a VW Beetle, and the giant short-faced kangaroo, which grew to be ten feet tall. Then all of the continent's largest animals disappeared. Every species of marsupial weighing more than two hundred pounds—there were nineteen of them—vanished, as did three species of giant reptiles and a flightless bird with stumpy legs known as Genyornis newtoni.

  This die-off roughly coincided with the arrival of the first people on the continent, probably from Southeast Asia. Australia is a big place, and there couldn't have been very many early settlers. For a long time, the coincidence was discounted. Yet thanks to recent work by geologists and paleontologists, a clear global pattern has emerged. About 11,000 years ago, three-quarters of North America's largest animals—among them mastodons, mammoths, giant beavers, short-faced bears, and saber-toothed tigers—began to go extinct. This is right around the time the first humans are believed to have wandered onto the continent across the Bering land bridge. In relatively short order, the first humans settled South America as well. Subsequently, more than thirty species of South American "megamammals," including elephant-size ground sloths and rhinolike creatures known as toxodons, died out.

  And what goes for Australia and the Americas also goes for many other parts of the world. Humans settled Madagascar around 2,000 years ago; the island subsequently lost all mammals weighing more than twenty pounds, including pygmy hippos and giant lemurs. "Substantial losses have occurred throughout near time," Ross MacPhee, a curator at the American Museum of Natural History, in New York, and an expert on extinctions of the recent geological past, has written. "In the majority of cases, these losses occurred when, and only when, people began to expand across areas that had never before experienced their presence." The Maori arrived in New Zealand around eight hundred years ago. They encountered eleven species of moas—huge ostrichlike creatures without wings. Within a few centuries—and possibly within a single century—all eleven moa species were gone. While these "first contact" extinctions were most pronounced among large animals, they were not confined to them. Humans discovered the Hawaiian Islands around 1,500 years ago; soon afterward, 90 percent of Hawaii's native bird species disappeared.

  "We expect extinction after people arrive on an island," David Steadman, the curator of ornithology at the Florida Museum of Natural History, has written. "Survival is the exception."

  Why was first contact with humans so catastrophic? Some of the animals may have been hunted to death; thousands of moa bones have been found at Maori archaeological sites, and man-made artifacts have been uncovered near mammoth and mastodon remains at more than a dozen sites in North America. Hunting, however, seems insufficient to account for so many losses across so many different taxa in so many parts of the globe. A few years ago, researchers analyzed hundreds of bits of emu and Genyornis newtoni eggshell, some dating from long before the first people arrived in Australia and some from after. They found that around 45,000 years ago, rather abruptly, emus went from eating all sorts of plants to relying mainly on shrubs. The researchers hypothesized that Australia's early settlers periodically set the countryside on fire—perhaps to flush out prey—a practice that would have reduced the variety of plant life. Those animals which, like emus, could cope with a changed landscape survived, while those which, like Genyornis, could not died out.

  When Australia was first settled, there were maybe half a million people on Earth. There are now more than 6.5 billion, and it is expected that within the next three years the number will reach 7 billion.

  Human impacts on the planet have increased proportionately. Farming, logging, and building have transformed between a third and a half of the world's land surface, and even these figures probably understate the effect, since land not being actively exploited may still be fragmented. Most of the world's major waterways have been diverted or dammed or otherwise manipulated—in the United States, only 2 percent of rivers run unimpeded—and people now use half the world's readily accessible freshwater runoff. Chemical plants fix more atmospheric nitrogen than all natural terrestrial processes combined, and fisheries remove more than a third of the primary production of the temperate coastal waters of the oceans. Through global trade and international travel, humans have transported countless species into ecosystems that are not prepared for them. We have pumped enough carbon dioxide into the air to alter the climate and to change the chemistry of the oceans.

  Amphibians are affected by many—perhaps most—of these disruptions. Habitat destruction is a major factor in their decline, and agricultural chemicals seem to be causing a rash of frog deformities. But the main culprit in the wavelike series of crashes, it's now believed, is a fungus. Ironically, this fungus, which belongs to a group known as chytrids (pronounced "kit-rids"), appears to have been spread by doctors.

  Chytrid fungi are older even than amphibians—the first species evolved more than 600 million years ago—and even more widespread. In a manner of speaking, they can be found—they are microscopic—just about everywhere, from the tops of trees to deep underground. Generally, chytrid fungi feed off dead plants; there are also species that live on algae, species that live on roots, and species that live in the guts of cows, where they help break down cellulose. Until two pathologists, Don Nichols and Allan Pessier, identified a weird microorganism growing on dead frogs from the National Zoo, chytrids had never been known to attack vertebrates. Indeed, the new chytrid was so unusual that an entire genus had to be created to accommodate it. It was named Batrachochytrium dendrobatidis—batrachos is Greek for "frog"—or Bd for short.

  Nichols and Pessier sent samples from the infected frogs to a mycologist at t
he University of Maine, Joyce Longcore, who managed to culture the Bd fungus. They then exposed healthy blue poison-dart frogs to it. Within three weeks, the animals sickened and died.

  The discovery of Bd explained many of the data that had previously seemed so puzzling. Chytrid fungi generate microscopic spores that disperse in water; these could have been carried along by streams or in the runoff after a rainstorm, producing what in Central America showed up as an eastward-moving scourge. In the case of zoos, the spores could have been brought in on other frogs or on tracked-in soil. Bd seemed to be able to live on just about any frog or toad, but not all amphibians are as susceptible to it, which would account for why some populations succumbed while others appeared to be unaffected.

  Rick Speare is an Australian pathologist who identified Bd right around the same time that the National Zoo team did. From the pattern of decline, Speare suspected that Bd had been spread by an amphibian that had been moved around the globe. One of the few species that met this condition was Xenopus laevis, commonly known as the African clawed frog. In the early 1930s, a British zoologist named Lancelot Hogben discovered that female Xenopus laevis, when injected with certain types of human hormones, laid eggs. His discovery became the basis for a new kind of pregnancy test and, starting in the late 1930s, thousands of African clawed frogs were exported out of Cape Town. In the 1940s and '50s, it was not uncommon for obstetricians to keep tanks full of the frogs in their offices.