CHAPTER I THE SIXTH EXTINCTION
Atelopus zeteki
The town of El Valle de Antón, in central Panama, sits in the middle of a volcanic crater formed about a million years ago. El Valle has one main street, a police station, and an open-air market. In addition to Panama hats and vividly colored embroidery, the market offers what must be the world’s largest selection of golden-frog figurines. There are golden frogs resting on leaves and golden frogs sitting up on their haunches and—rather more difficult to understand—golden frogs clasping cell phones. The golden frog, which is taxicab yellow with dark brown splotches, is considered a lucky symbol in Panama; its image is (or at least used to be) printed on lottery tickets.
As recently as a decade ago, golden frogs were easy to spot in the hills around El Valle. One creek was nicknamed Thousand Frog Stream. A person walking along it would see so many golden frogs sunning themselves on the banks that, as one biologist who made the trip many times put it to me, “it was insane—absolutely insane.”
The golden frogs of El Valle
Then the frogs around El Valle started to disappear. The problem was first noticed to the west, near Panama’s border with Costa Rica. An American graduate student happened to be studying frogs in the rain forest there. She went back to the States for a while, and when she returned, she couldn’t find any frogs. She had no idea what was going on, but, since she needed frogs for her research, she set up a new study site. At first, the frogs at the new site seemed healthy; then, the same thing happened. The blight spread through the rain forest until little corpses began showing up just outside El Valle.
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I first read about the frogs of El Valle in a nature magazine I borrowed from my kids. The article was illustrated with photos of the golden frog and other brilliantly colored species. It told the story of the spreading scourge and described biologists’ efforts to get out in front of it. The biologists had raced to save as many animals as possible, even though they had nowhere to keep them. So what did they end up doing? They put them “in a frog hotel, of course!” The “incredible frog hotel”—really a local bed-and-breakfast—agreed to let the frogs stay (in their tanks) in a block of rented rooms.
“With biologists at their beck and call, the frogs enjoyed first-class accommodations that included maid and room service,” the article noted. The frogs were also served delicious fresh meals—“so fresh, in fact, the food could hop right off the plate.”
Just a few weeks after I read about the “incredible frog hotel,” I ran across another frog-related article. It was titled: “Are We in the Midst of the Sixth Mass Extinction? A View from the World of Amphibians.” Its authors, a pair of conservation biologists, noted that there “have been five great mass extinctions during the history of life on this planet.” The first took place some 450 million years ago, when living things were still mainly confined to the water. The most recent mass extinction came at the close of the Cretaceous period; it wiped out the dinosaurs. The article argued that an event of a similarly catastrophic nature was currently underway. It was illustrated with just one photograph, of a dozen yellow-legged frogs—all dead—lying bloated and belly-up on some rocks.
I understood why a kids’ magazine had opted to publish photos of live frogs rather than dead ones. I also understood the impulse to play up the cute idea of amphibians ordering room service. Still, the notion that a mass extinction event would be taking place right now, more or less in front of our eyes, struck me as mind-boggling. Surely this story, too—the bigger, darker, far more consequential one—deserved telling. If a sixth mass extinction is underway, then those of us alive today are not only witnessing one of the rarest events in life’s history, we are also causing it. A few days after I read the article, I booked a ticket to Panama.
* * *
The El Valle Amphibian Conservation Center, or EVACC (pronounced “ee-vac”), was created to replace the “incredible frog hotel.” It lies along a dirt road near the open-air market where the golden-frog figurines are sold and is filled entirely with tanks. There are tall tanks for frogs that live in forest canopy, like the lemur tree frog. And shorter tanks for species that live on the forest floor, like the big-headed robber frog. A few dozen tanks are reserved for Panamanian golden frogs, Atelopus zeteki.
Golden frogs have an ambling gait that makes them look a bit like a dizzy person trying to walk a straight line. They have long, skinny limbs, pointy yellow snouts, and very dark eyes that look intelligent. In the wild, females lay their eggs in shallow, running water; males, meanwhile, defend their territory from the tops of mossy rocks. In EVACC, each golden-frog tank has its own running water, provided by its own little hose, so that the animals can breed near a simulation of the streams that were once their home. In one of the fake streams, I noticed a string of little pearl-like eggs. On a whiteboard nearby someone had noted excitedly that one of the frogs “depositó huevos!!”
EVACC sits more or less in the middle of the golden frog’s range, but it is entirely cut off from the outside world. Nothing comes into the building that has not been thoroughly disinfected, including the frogs, which, in order to gain entry, must first be treated with a solution of bleach. Human visitors are required to wear special shoes and to leave behind any bags or knapsacks or equipment that they’ve used out in the field.
EVACC’s director is Panamanian Edgardo Griffith. Griffith is tall and broad-shouldered, with a round face and a wide smile. He wears a silver ring in each ear and has a large tattoo of a toad’s skeleton on his left shin. Griffith told me that he thought a key part of his job was getting to know the frogs as individuals. “Every one of them has the same value to me as an elephant,” he said.
The first time I visited EVACC, Griffith pointed out to me several species that are now extinct in the wild. These included, in addition to the Panamanian golden frog, the Rabb’s fringe-limbed tree frog, which was first identified only in 2005. At the time of my visit, EVACC was down to just one Rabb’s frog. The frog, greenish-brown with yellow speckles, was about four inches long, with oversize feet that gave it the look of a gawky teenager. Rabb’s fringe-limbed tree frogs laid their eggs in tree holes. In an unusual, perhaps even unique arrangement, the male frogs cared for the tadpoles by allowing their young, quite literally, to eat the skin off their backs. Griffith said that he thought there were probably many species that had, by now, entirely vanished; it was hard to say how many, since most of them were probably unknown to science.
“Unfortunately,” he told me, “we are losing all these amphibians before we even know that they exist.”
He went on: “Even the regular people in El Valle, they notice it. They tell me, ‘What happened to the frogs? We don’t hear them calling anymore.’”
* * *
Amphibians are among the planet’s great survivors. Since they crawled out of the water some 400 million years ago, amphibians have adapted to conditions on every continent except Antarctica. The greatest numbers are found in the tropical rain forests, but there are some, like the sandhill frog of Australia, that can live in the desert. Several common North American frogs, including spring peepers, are able to survive the winter frozen solid, like Popsicles.
David Wake is one of the authors of the article that sent me to Panama. Initially he found it hard to believe that amphibians were disappearing. When Wake’s students began returning from frog-collecting trips in the Sierra Nevada empty-handed, he assumed that his students were going to the wrong spots, or that they just didn’t know how to look. Then a graduate student with several years of collecting experience told him that he couldn’t find any amphibians, 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.”
Part of what made the situation so mystifying was the geography; frogs were vanishing from populated areas but also from pristine places, like the Sierras and the mountains of Central America. Rare and highly specialized species were vanishing but so, too, were more familiar ones. In Ecuador, the jambato toad, a frequent visitor to backyard gardens, disappeared in a matter of years. And in northeastern Australia, the southern day frog, once one of the most common in the region, could no longer be found.
The first clue to the mysterious killer’s identity came not from the wild but from a zoo. The Smithsonian’s National Zoo, in Washington, DC, had been successfully raising blue poison-dart frogs, which are native to Suriname, through many generations. Then, more or less from one day to the next, the zoo’s tank-bred frogs started dropping. A veterinary pathologist took some samples from the dead frogs and ran them through an electron scanning microscope. He found a strange microorganism on the animals’ skin, which he eventually identified as a fungus belonging to a group known as chytrids.
Bactrachochytrium dendrobatidis (Bd fungus) under a microscope
Chytrid fungi turn up nearly everywhere; they can be found at the tops of trees and also deep underground. This particular species, though, had never been seen before; and so a new name had to be created for it. It was dubbed Batrachochytrium dendrobatidis—or Bd for short.
To make sure that Bd was the culprit, scientists at the National Zoo deliberately exposed healthy blue poison-dart frogs to the fungus. Within three weeks, they were dead. Subsequent research showed that Bd causes the frogs to suffer what is, in effect, a heart attack.
By now, Bd has spread through Panama and Columbia, and through the highlands of South America and the eastern coast of Australia. It has crossed into New Zealand and Tasmania. It has raced through the Caribbean and has been detected in Italy, Spain, Switzerland, and France. At this point, Bd appears to be, for all intents and purposes, unstoppable.
* * *
In ordinary times, extinction takes place only very rarely at what’s known as the background extinction rate. This rate varies from one group of organisms to another. For what’s probably the best-studied group, which is mammals, it’s been reckoned that you’d expect—very roughly—one species to disappear every seven hundred years.
Mass extinctions are different. Instead of a background hum there’s a crash, and disappearance rates spike. The background rate for amphibians is probably lower than it is for mammals. Probably, one amphibian species should go extinct every thousand years or so. That species could be from Africa or from Asia or from Australia. In other words, the odds of an individual’s witnessing such an event should be effectively zero. Already, Griffith has observed several amphibian extinctions. Pretty much every herpetologist working out in the field has watched several. (Even I, in the time I spent researching this book, encountered one species that has since gone extinct and three or four others, like the Panamanian golden frog, that are now extinct in the wild.)
“I sought a career in herpetology because I enjoy working with animals,” a herpetologist at Zoo Atlanta has written. “I did not anticipate that it would come to resemble paleontology.”
Today, amphibians are the world’s most endangered class of animals; it’s been calculated that the group’s extinction rate could be as much as forty-five thousand times higher than the ordinary background rate. But extinction rates among many other groups are approaching amphibian levels. It is estimated that one-third of all species of coral, a third of all freshwater mollusks, a third of sharks and rays, a quarter of all mammals, a fifth of all reptiles, and a sixth of all birds are headed toward oblivion. The losses are occurring all over—in the South Pacific and in the North Atlantic, in the Arctic and the Sahara, in lakes and on islands, on mountaintops and in valleys. If you know how to look, you can probably find signs of the current extinction event in your own backyard.
There are all sorts of disparate reasons that species are disappearing. But trace the process far enough and inevitably you are led to the same culprit: us.
Bd is capable of moving on its own. The fungus generates microscopic spores with long skinny tails; these propel themselves through water and can be carried far longer distances by streams, or in the runoff after a rainstorm. But Bd cannot leap over mountains or swim across oceans. So how did it get to so many parts of the world more or less simultaneously? One theory has it that Bd was moved around the globe with shipments of African clawed frogs, which were used in pregnancy tests. A second theory holds that the fungus was spread by North American bullfrogs, which are often exported for human consumption.
Either way, the logic is the same. Without being loaded by someone onto a boat or a plane, it would have been impossible for a frog carrying Bd to get from Africa to Australia or from North America to Europe. This sort of intercontinental reshuffling, which nowadays we find totally unremarkable, is probably unprecedented in the 3.5-billion-year history of life.
* * *
Even though Bd has already swept through most of Panama, Griffith still occasionally goes out collecting for EVACC, looking for survivors. I scheduled my visit to coincide with one of these collecting trips, and one day I set out with him and two American biologists through the rain forest.
The trail wound its way through the trees 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.
One of the Americans, 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, 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,” he assured me.
Howler monkeys screamed in the distance. Griffith pointed out jaguar prints in the soft ground.
After about an hour, we came to a farm that someone had carved out of the trees. There was some scraggly corn growing, but no one was around, and it was hard to say whether the farmer had given up on the poor rain forest soil or was simply away for the day. A flock of emerald-green parrots shot up into the air. After another several hours, we emerged into a small clearing. A blue morpho butterfly flitted by, its wings the color of the sky. There was a small cabin on the site, but it was so broken down that everyone elected to sleep outside. Griffith helped me string up my bed—a cross between a tent and a hammock that had to be hung between two trees.
That evening, Griffith prepared some rice on a portable gas burner. After eating it, 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 number one of rain forest safety: Never grab on to something if you don’t know what it is. After a particularly messy fall, a biologist pointed out to me a tarantula the size of my fist on a nearby tree.
Practiced hunters can find frogs at night by shining a light into the forest and looking for the reflected glow of their eyes. The first amphibian Griffith sighted this way was a glass frog, perched on top of a leaf. Glass frogs are so named because their translucent skin reveals the outline 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 completely still and then, with a heron-like 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. He put the Q-tip in a little plastic vial—it would later be sent to a lab and analyzed for Bd.
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 animal, 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 mating. Griffith left these two alone.
One of the amphibians 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—by this point we were walking in the stream—we heard the call, which seemed to be emanating from several directions at once. Griffith began imitating the call, making a cork-popping sound with his lips. Eventually, he gestured us over, and we found him standing in front of a large yellow frog with long toes and an owlish face.
“You are a beautiful boy,” he murmured to the frog.
Text copyright © 2023 by Elizabeth Kolbert
Illustrations copyright © 2023 by Jessica Roux
