[INDISTINCT BACKGROUND SOUNDS] [MUSIC PLAYING] “We might call that a cold case, right? There’s no evidence. There’s no — there’s no murder weapon. There’s no crime. It’s a crime scene, but the culprit, the criminal, has left. It was just — it was incredible, because everything was big, abundant, weird, fascinating birds and animals running all over the place. And the first night we were there, we go out into this beautiful stream.” [FOREST SOUNDS] “There is moss everywhere. It’s just draping the trees. It’s on the ground. And everything is wet and sodden. And the most amazing frog is sitting on a leaf right in front of us. And it kind of glows in the light of our lamps. It’s fluorescent. So it’s green, and it’s spiny. And it’s got this white chin pouch. And every time the male calls, he goes, ‘Peep!’ And you can see this white thing expand. And the white and the green shine in the light of our lights. So they sort of look like little jewels. And so we’re like, ‘What are these things?’ And it turned out that these frogs were really cool. They had on their thumbs a whole bunch of little black spines they use as weapons. And so what apparently happens is a new male will show up on a transect. And he’ll see a really nice territory. And he’ll want to sit there and call for females there. Well, if there’s a resident male there, one who’s already there, he’ll be like, ‘No, this is my plant. I’m staying here. This is the best plant for those females.’ And they will fight.” [SUSPENSEFUL MUSIC] “They kind of arm — they wrestle like little sumo wrestlers. And they use their thumbs to scratch. So you’ll see, like, around their neck and shoulders, scratches. And so what you would see is you would see a really great male. He was the king of that stream. A few of them got almost all the girls, all the eggs, all the tadpoles. Most of them got nada, nothing.” [UNDERWATER SOUNDS] “For almost two years, I lived in this little shack we called La Casita. And I would collect all these tadpoles and bring them into my house. And I would raise these tadpoles up to try and figure out, well, how long does it take a tadpole to metamorph into an adult frog? So every afternoon, I would sit there and measure hundreds and hundreds and hundreds of tadpoles, listening to bad Costa Rican music. And then at night, I’d go back out and study mom and dad.” [FOREST SOUNDS] “Well, when I catch them, I do admit that I, like, ‘Ohhh, it’s male No. 2. Hello.’ That was sort of their name, like male No. 2, male No. 22, female 305. You really did come to understand the little personalities. You knew who was dominant. You knew which guy the girls really liked. You knew who had a really great territory. You knew the ones who were out all the time but were never successful. They tried and tried, but nada.” [MUSIC PLAYING] [DOOR OPENING] “And after about two years living in this little shack on the mountain, I go back to the University of Miami, write up all the research I’ve done. And I had to — I had to go back for one short little experiment. And when I go back, the frogs are gone.” [MUSIC PLAYING] “All of them. And I thought, ‘Well, you know, maybe it’s my fault. Maybe I bothered them too much. Maybe they really got scared and went away. And maybe I just need to wait long enough, and they’ll come back. Maybe it’s the weather. Maybe it’s not rainy enough.’ So I waited, and I waited, and I waited for a whole summer. And they never reappeared. I was left with no answer, which meant it had to be something I couldn’t see. But there was no smoking gun. And I started thinking about a place I had been to once in Panama. Very similar to this site in Costa Rica. Amazing little frogs. Tons of frogs all over the place. And so that became my new site. And for the next two or three years, I would go down, and I would count the numbers of species and how many of different sorts were out there.” [FOREST SOUNDS] “The third year I was there, after a couple days, we start noticing that many of them don’t look very good. They’re sick. They’re not able to move. They’re kind of shaking some of the time. And every day, we found more dead frogs. And as I sat there, I was thinking, ‘Oh, my goodness. This is probably what happened at my last site. But now I’m watching it.’” [MUSIC PLAYING] “We sent them off to labs and said, ‘Tell us why they died.’ And the person I sent them to, Dr. David Green, looked at them and said, ‘You know what? I’ve noticed that maybe 70 percent of them have some weird skin problem. I’ve never seen this before. I don’t know what it is.’ And they publish a picture in The New York Times of the thing in the skin. We don’t even know what to call it. And of course, it’s The New York Times, which goes all around the globe. And it turns out that people in Australia had a weird thing in the skin of their dead frogs. People in the National Zoo in Washington, D.C., had had a big die-off of frogs in their collection. And they had the same weird thing in the skin. And so these people called me up, and they said, ‘It kind of looks like this weird kind of fungus.’ This is probably the answer. The fungus needs frogs to reproduce. It tries to detect the skin of a frog. And if it does, the head of this little spermlike zoospore attaches to the skin, somehow is able to bury into the skin of the frog. It drops off the tail. And that head part then changes and makes this round, spherelike thing that becomes hollow. In the middle of it, new zoospores are produced. So this is the life cycle of the chytrid fungus. And that round sphere in the skin of the frog has a little tube, a little tunnel, that opens up to the outside. And those zoospores then pop out and either go swimming in the water or drop onto the skin of the frog and again drop their tail, create another hollow sphere, where they create more zoospores. It physically disrupts the skin. And the skin of an amphibian is very important. The frog can’t get oxygen. It also can’t get water. And at some point, the heart gives out, and the frog dies. So when you have a really high number of frogs that are infected, they are just pumping out millions and millions of zoospores that are then infecting all the other frogs. All these chytrids are moving about in the live animal trade, primarily for pets but also for things like food. People are taking a chytrid from Asia and moving it to Brazil. The chytrid that only lives in Brazil is being moved by us humans to the United States. The chytrid that is only found in the tip of South Africa has been moved into Europe. We have made it super easy for infectious diseases of all sorts to leave the jungle and get to a major city in a couple of hours. So it’s everywhere at this point. Even today, we don’t know how to cure wild frogs. We can treat captive frogs. No problem. You give them a bath in this antifungal mixture, and you can get rid of their infection. But in the wild, there’s no way to do that. There’s no way to stop that killer. You just simply have to watch them die. I mean, you sit there, and you feel terrible.” [HOSPITAL SOUNDS] “To remember what it was like to walk down a trail in the forest and see just these little jewels, to walk these streams and hear them calling, and you hear this incredible diversity, it’s like a symphony. And then to go back a year later maybe, and it’s silent. It’s totally quiet. And it’s so weird.” [ROLLING THUNDER] “When the dinosaurs died out, there were frogs. And somehow they survive this event that wiped out giant T. rex and brontosaurus. The estimate is somewhere between 150 and maybe 200 species have gone extinct in the past two or three decades. Forty-one percent of all amphibians are in decline. And that’s worse than any other group of animals on the planet. I mean, there’s certainly the harlequin frogs, Atelopus. These are beautiful, bright-colored toads that live in streams, almost completely eliminated around the globe. Then there’s the beautiful little glass frogs, ranas de cristales. You can see their green bones through their clear skin and watch their heartbeat. And they live on the leaves over the streams. There’s the frog I studied for my dissertation, and it’s called Isthmohyla calypsa. And it’s that spiny green frog. There was the golden toad, the famous golden toad from Costa Rica that completely disappeared. I’ll end on one that’s my Twitter avatar, which is Gastrotheca cornuta. And this is a big frog. He lives in the top of the trees, and he’s got horns over his eyes, so it looks like he’s got two horns coming out of his head. And they have a call that sounds like the popping of a champagne cork.” [CORK POPPING] “And they’re gone, too.” [MUSIC PLAYING] “And you keep waiting for them to come back — it’s very hard to comprehend that they’re gone forever — and that magically, one day, things will be better. You know it’s probably not going to happen, but you can’t say for sure until you have to keep checking. Are they back yet? How are they doing? What’s going on?”