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Sounds of Silence on the Continental Divide

Frogs and other amphibians are an enigma to me. My training has given me expertise in what makes the scaled creatures we know as reptiles tick, but frogs? I learned about them a bit as a herpetology student, and then I figured out a little more from teaching my own herpetology classes. However, I live in California where snakes and lizards dominate the landscape.

I heard stories from colleagues about wet and wild places in the world where frogs thrived, so much so that you could holler at the top of your lungs right next to someone and they still couldn’t hear you. My graduate program offered a semester-long tropical ecology course, but my research advisor told me I had too much work to do in the desert. The tropics would have to wait.

In 2009, as a young assistant professor, I was invited to the Continental Divide in the Panamanian highlands to help a colleague plan their field biology class. Finally, I would have the opportunity to experience the tropics in all their glory: from the silent snakes to the bellowing frogs; from the sweet mountain air to the savory food; from the clear streams to the landscapes cloaked in green. The Continental Divide is a mountainous area that runs through the middle of Central America and gives rise to and separates the watersheds on the Pacific and Atlantic sides. Lush and wet, this area famously houses an incredible diversity of wildlife, from insects to birds to frogs.

What I didn’t know was that I was going to bear witness to the fallout from a crumbling tropical community due to a deadly fungus that had arrived five years ahead of me.

We traveled to an extremely remote national park officially named Parque National Omar Torrijos after Panama’s beloved leftist dictator of the 1970s, but often called El Copé after the nearby town of about 1200 people. The dirt road from El Copé to the park was wet, slippery, and pockmarked heavily with the tracks of other four-wheel-drive vehicles that had made the journey. When we emerged from the vehicle, I found myself in a small parking lot next to thick primary forest, completely shrouded in clouds. It wasn’t exactly raining, yet moisture dripped from the air in that peculiar way of cloud forests. We spread out through the forest to look for creatures.

Verdant vine-wrapped trees stippled with epiphytes enclosed us in a solid blanket of that healthy rainforest smell that I wish could be bottled up and used as a home fragrance. The fungus-rich soils beneath my feet sprang back after I stepped, leaving no trace of my tracks. Moisture dripped from the foliage to join the streams that looped around the trees, pooling here and there before making its gradual way down the northern slope where it would join the Belén and Coclé del Norte Rivers before emptying into the Caribbean Sea. Omar Torrijos National Park was the picture of a perfect, healthy cloud forest.

Except for one major thing.

The forest was completely silent.

Prior to 2004, the pools and streams would have been crawling (or swimming, hopping, jumping, or other froggy word of your choice) with amphibians. Tiny long-legged bodies would have scattered under our feet as we stepped through the leaf litter. There would have been an ear-splitting cacophony of male frogs singing their hearts out to attract females.

But most of those frogs had died five years earlier, resulting in the heart-breaking collapse of an entire amphibian community due to a microscopic fungus that had swept north to south through Central America in a wave of destruction.

No more Giant Glass Frogs (Sachatamia ilex) showing off their internal organs through transparent skin.

No more Clown Frogs (Atelopus varius), whose territorial battles start when males wave at one another because the gurgling water drowns out their squeak-like vocalizations, and whose females stomp on males who invade their territories.

No more of at least twelve different species of Brittle-Belly Frogs (Craugastor spp.), which skip the tadpole stage and develop directly into little toadlets.

Tropical rainforests are complex ecosystems, where species are connected to one another via fragile threads that are invisible when the system is healthy. However, pull one thread, and the entire web can fall apart. In the five years since the fungus had hit, how had the community of Omar Torrijos National Park been affected by the mass die-off of frogs?

I got my first answer when someone hollered Frog! I crashed through the forest toward the voice, ducked under a thick vine, and splashed into a stream … but I didn’t make it across. As soon as I stepped into the cold water, my boots slipped right out from under me and I was on my back.

I had expected finally to learn all about frogs during my trip to Panama. And learn I did, but not in the way that I had expected. Falling unceremoniously into the stream was my firsthand experience of one way in which amphibians play an important role in the environment. Ordinarily, hordes of tadpoles nosh away on algae with keratinous little beaks. After the fungus arrived, the collective loss of so many of these nibblers led to the gradual buildup of huge, slippery slabs of algae on all underwater surfaces, just waiting to gleefully flip unsuspecting biologists onto their backs.

Sputtering, I hoisted myself up and out of the water, shook myself off like a dog, and ran over to where a flashlight was trained on a small rock on the ground. Sure enough, a little frog about the size of a silver dollar sat shining in the beam, its big eyes peering up at us, its toes flared out to form enlarged round pads.

A treefrog? I inquired.

Looks like a Smilisca sila, my colleague confirmed.

The Panama Cross-Banded Treefrog is an extremely common frog, ranging from southern Costa Rica through most habitats in Panama down to central Colombia. This is one of the few species that survived the fungal assault. I kneeled down and gently cupped the little frog into my hand. As I positioned it this way and that to take photos, it tracked me with its big, black pupils, which were surrounded by brilliant, glittery gold flecks.

As I placed the treefrog back onto its perch for more photos, I heard someone call Snake! in the distance. This got me moving again. Searching for snakes in a tropical rainforest is like looking for a needle in a haystack, except you’re never sure if the needle is even there to begin with, the needle can move around, and sometimes the needle is highly venomous.

Adrenaline pumping, I raced through the forest, slowing only to carefully plod through streams to avoid another dip, and found a colleague with their flashlight trained on a patch of vegetation about head height.

Where is it? I don’t see it! I squeaked.

Laughing, my colleague held out one of the vines. But it wasn’t a vine, it was a snake!

I was looking at a Cope’s Vine Snake (Oxybelis brevirostris), a true marvel of camouflage, stealth, and beauty. As you might guess by its name, this snake is a vine mimic, its long, skinny, emerald-hued body allowing it to literally disappear into mats of vegetation. It glared at me with the ultimate snake side-eye as it hoisted the front half of its body into the air, effortlessly weightless in its search of a branch on which to mount its escape.

Okay, Okay, you can go back to bed. I arranged the snake in the tree to snap some photos, and at the first chance, it glided silently into the thick canopy.

I later found out that vine snakes have always been one of the most common snakes in the park. However, locals mused that the vine snake didn’t seem to be as common anymore as it used to be. In fact, in the five years since the sudden loss of frogs, most snakes seemed to have declined in the park as well.

What would frogs have to do with snakes? Well, as was the case with the stealthy vine snake, many snakes in the park eat primarily or even exclusively frogs. Pulling the frog thread led to the unraveling of the entire food web. When the frogs died out, so did the snakes, or so the hypothesis went. Given how hard it is to actually find tropical snakes even when they’re abundant, it took 10 more years until the tricky math was worked out to document declines in secretive species like snakes. In 2020, a study was published in the journal Science showing a crash in snake species diversity in the park following the 2004 amphibian decline. Vine snakes made it through intact, but those encountered by scientists were typically even skinnier than their natural svelte state.

Why did some frogs and snakes survive, while others went extinct? Why have some species recovered since the first wave of fungus arrived, taking advantage of the decrease in competition, while others exist now only in captive collections where zookeepers fastidiously breed them in the hopes that their distant offspring may one day be released back into the wilds of El Copé and other tropical landscapes devastated by the chytrid fungus?

I was merely a tourist to this remote rainforest, but my colleagues toil every year in search of answers to these questions. As I packed my luggage to return home to California, it occurred to me that the biologists fighting for the survival of these meek forest creatures are true heroes. The amphibian declines that began in earnest in the 1980s were a classic canary in the coal mine scenario, acting as a warning to us all about what could happen to other wildlife. More recently, scientists all over the world have sounded the alarm about the collapse of other wild communities, from insects to coral reefs to birds. In some cases, recovery efforts based on sound science have worked: reintroducing wolves into Yellowstone restored the elk-chewed landscape; beavers reintroduced to English forests improved soil quality and reduced flooding; the Leonardo DiCaprio Foundation and Fundación Rewilding Argentina have invested millions of dollars into restoring a fractured landscape in Argentina by reintroducing tapirs, peccaries, and giant anteaters with plans in motion to add jaguars back to this rich area where they historically thrived. Even at El Copé, the recovery of certain frog species is slowly restoring the ecosystem.

A disease had silenced the forest I visited in Panama, a scenario mirrored in hundreds of other forests and wetlands around the world. But loud are the conservation biologists and zookeepers who tirelessly advocate for the frogs that once made these forests ear-splitting cacophonies of life. Because of their efforts, future visitors to El Copé might have wildlife encounters beyond my lonely treefrog and vine snake and might experience the forest as it once was—a verdant, pulsing hotspot of chirping, beeping, and wailing sirens made by dozens of species of vocalizing amphibians calling their hearts out, as the snakes slink among them in search of lunch.