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Climbing Into The Secret World Of An Ancient Bornean Rainforest

Dangling on a rope some 40 feet up, amid a labyrinth of leafy tree limbs, I looked down and questioned my sanity for asking the two men far below to hoist me into the canopy of this rainforest. One of them, photographer Tim Laman, had tied a line to an arrow and shot it over a high bough. Then he and his assistant rigged a pulley system to lift me to a place few humans get to visit. With each of their heaves, the rope squeaked and the branch above bounced precariously.

The aim of this adventure was to reach a high crotch in a 150-foot-tall Shorea tree, whose genus includes some of the world's tallest. A spot among its high branches would offer an ideal view of one of the last remaining intact lowland rainforests left in Southeast Asia. Located just below the Equator, Gunung Palung National Park is a 417-square-mile protected area that encompasses the Palung and Panti mountains in the Indonesian part of Borneo. (The island is divided among three nations: Indonesia, Malaysia, and Brunei.) An area around Mount Palung was first designated as a natural reserve in 1937; over the years its borders were stretched, and in 1990 the Indonesian government designated it a national park. Today it covers nine distinct forest types stacked one atop another across a series of steep slopes, moving up from mangrove and peat swamp to mossy mountaintop forest.

Once the guys hauled me as high as they could, the rest of the climb was on me. It was agonizingly slow, nothing like the easy scramble I'd seen other primates make into the treetops. As I inched up the rope, my arms ached, my left sock squished with blood from a leech bite, and I was marinating in sweat.

But it would be worth it, I reasoned, because of what lives in that green world overhead. All week I'd reveled in the cackles of leaf monkeys, hoots of gibbons, and barks of macaques, plus choruses of birds and frogs—all backed by the hums and whines of insects. Since the canopy is home to these musicmakers, I hoped to glimpse something animal from a perch at their eye level.

Truth be told, I was most excited to meet the island's biggest stars: the orangutans. The flaming-orange-haired primates are the only great ape native to Asia, and the Bornean orangutan, Pongo pygmaeus, has long represented the soul of Gunung Palung while playing a crucial role in the health of its forests. Some 2,500 of them roam these treetops, a healthy number considering they're critically endangered. And when Laman mentioned he could get me up into their domain, I was game.

A Bornean horned frog nearly disappears in leaf litter, its camouflage affording an advantage over insects it hunts. The frog's distinctive honk is one of countless calls filling the rainforest's diverse soundscape. While this creature is found on other nearby islands, more than 70 percent of Gunung Palung's amphibian species live only on Borneo.

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At about a hundred feet, I was well below the top of the canopy but high enough that I could see the curve of a fog-shrouded mountain rising over densely forested parkland. I swung myself into the fork of two large limbs and settled in to admire the view and, with luck, spot something furry or feathered. Time passed. I gazed and listened expectantly. The branches gently swayed, and the whisper of leaves taunted me; otherwise, all remained quiet. More time passed. No glorious birds came to feed; no chattering primates swung by. Even the insects seemed to be on a break. I wasn't surprised—the time of day and dearth of fruit in this tree weren't ideal for wildlife spotting. Still, I was a bit disappointed that nobody was home.

Gunung Palung lies in Borneo's swampy southwest, within the Indonesian province of West Kalimantan. For scientists, the park's remoteness and limited tourism are pluses: Gunung Palung presents a veritable time capsule of what the island was like for millennia. By exploring this primal world directly, I'd hoped to view its wonder with fresh eyes and discover more about how life here continues thriving.

Some of the biggest clues were right in front of me, but I'd already missed them.

Red leaf monkeys, including this female with her infant, eat figs year-round and other fruits as they ripen. The primates, known for their cackling calls, have adapted well to the young secondary forests that have filled in where old-growth trees were cut down.

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Borneo's rainforest has been evolving for millions of years, a process that has yielded a bounty of unique flora: Consider its more than a thousand types of orchids, or its dozens of kinds of carnivorous pitcher plants, or its 3,000-plus tree species, including the towering yellow meranti that can grow taller than the Statue of Liberty.

Somewhere out there are clouded leopards, pygmy elephants, flying foxes, flying frogs, flying lemurs, flying snakes, nearly 700 species of birds, about a hundred species of bats, and more than a thousand kinds of ants. And let's not forget the gazillion other insects, reptiles, amphibians, spiders, fungi, and microbes. It's a living forest and unlike any other on Earth.

Among the first botanists to inform the Western world's imagination about these marvels was an Italian named Odoardo Beccari, who visited the island in 1865. He was 21 years old and fresh from university when he arrived in Borneo to wander its "great forests." His account of those travels is filled with descriptions of otherworldly flora and other organisms. He encountered the massive Rafflesia flower, which featured nearly two-foot-wide scarlet petals and smelled like a rotting corpse, and a phosphorescent fungus that emitted enough light at night to allow him to read a newspaper.

A male great argus, one of the world's largest pheasant species—they can reach up to six and a half feet, beak to tail tip—woos a potential mate with a grand display of giant eyespot-covered wing feathers, plus a little dance. Males clear away sticks and leaves to keep a "stage" for performing.

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To Beccari, the jungle seemed a riot of plants ruthlessly scheming and strategizing. He marveled at how orchids and other flowering plants made their way into the upper stories of the mightiest trees to reach the sunlight and used their brilliant colors, peculiar shapes, and powerful odors to attract insects that helped them pollinate and propagate. "To ensure success," Beccari wrote, "nature uses every possible artifice, every sort of deceit, every kind of cruelty."

The temptation might be to assume that this complex ecosystem flourished because there were no humans to disrupt it. But people have been living on Borneo for at least tens of thousands of years. The oldest known figurative painting—thought to depict a wild cowlike animal—was found in a Bornean cave and dated to at least 40,000 years ago. And as seafaring advanced, traders from throughout Asia, and later Europe, flocked to the island for its trees, minerals, and animals.

Today the list of resources extracted from Borneo reads like a modern plunderer's shopping list: timber, gold, diamonds, bauxite, coal, natural gas, and animals poached for the pet trade or traditional medicine. But the most devastating losses have come with the conversion of forest to agriculture, including oil palm farms, which yield a substance widely used in packaged foods and other products. Drought-related fires have also depleted old-growth trees, and in the late 1990s, political and economic turmoil in the region fueled an explosion of illegal logging and mining. All told, it's estimated that Indonesian Borneo lost nearly a third of its forest from 1973 to 2010.

While the illicit timber trade has been reduced in and around Gunung Palung, the region's volatile history gives my visit a sense of urgency. Cheryl Knott, a Boston University primatologist who leads orangutan studies in the park, told me that while the forest inside its borders has recovered fairly well—especially with improved law enforcement and as research and conservation work has expanded and provided jobs to locals—"without continued vigilance, things could easily go the other way."

Morning mist touches down in the lowland rainforest that carpets Mount Palung. The national park contains nine distinct forest habitats, rising in a series of steep slopes from mangroves and peat swamps to mossy mountaintops.

Photograph by TIM LAMAN, WITH DRONE PILOT TRI WAHYU SUSANTO

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For more than three decades, Cheryl Knott and Tim Laman, who are married, have been coming to Borneo to study, photograph, and unlock more secrets about its wild things. In 1994 Knott began a long-term study of orangutan ecology and behavior at the park's small research station and has led the project ever since. She invited me to visit the site, and after two days and nights of travel that landed me in West Kalimantan's capital, Pontianak, followed by a flight to Ketapang, a jarring truck ride, and a six-hour hike with two river crossings, I reached the Cabang Panti Research Station in the west-central section of the park.

The rustic compound consists of three wooden buildings that serve as laboratory, workspace, kitchen, and staff living quarters, arranged around a sandy yard on the bank of the Air Putih River. In the woods nearby, a few cabins on stilts house a rotating mix of 20 or so researchers and visiting university students. As a species that's crucial to the vitality of the whole region, orangutans are the main focus, but there are projects focused on other parts of this complex ecological web. I met Endro Setiawan, for example, who is working to create a complete database of Gunung Palung's trees.

Flanked by huge buttresses of the fruiting tree Dialium, researchers (from left) Zakaria, Ari Marlina, and Sahril Ramadani watch and collect data on orangutans in the forest canopy. A research initiative, now called the Gunung Palung Orangutan Conservation Program, was established in 1994 and focuses on the apes' habitat and how they respond to fluctuations in their food supply.

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After my mission into the forest canopy, I spent the rest of my hours with my feet on the ground, wandering. Like Beccari roughly 160 years ago, I was awed by the seemingly infinite life-forms that make up the forest. I watched red leaf monkeys and macaques scampering to outflank one another in the canopy. Paper kite butterflies the size of my palm fluttered by. I had to stare hard to spot a lime-green pit viper camouflaged on a twig beside the trail. During a breath-stealing dip in the river, I noticed a three-foot monitor lizard hunting for fish and a softshell turtle nosing the bank. Back in the forest, a Wallace's flying frog sprang from a tree—its spindly legs and webbed toes spread-eagle—seeming more bat than amphibian. I delighted in the song of the white-rumped shama, which makes it a prime target for the pet trade, and looked forward to the daily visit of a blue-eared kingfisher, which flew down the river at the same time each evening. And at night I shone my flashlight on patterned tree frogs—pupils dilated, ready to nab any insect that would fit in their mouths—and on lizards and birds asleep on overhanging limbs.

Most nights it rained in torrents. Thunder rolled and boomed. In the morning the river was bloated, its current rampaging. But within hours the water had dropped, having washed into the swamp forest and soaked into the sandy soil. The forest glistened.

Rarely seen, little studied, and considered vulnerable to extinction, a Sunda clouded leopard sets off a camera trap near Cabang Panti Research Station. The cats, which are most active at night, have broad paws, flexible hind legs, and long tails that equip them for climbing trees, descending headfirst, and even hanging from branches while gripping their prey. They're known to eat everything from monkeys, deer, and pigs to fish, civets, and porcupines.

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One morning I decided to hike a trail that led up 3,500 feet of elevation, through five of the nine forest habitats. Starting near the research station, in the tall, lowland dipterocarp forest, the early going was gentle but soon wound up a steep, mud-slick track. The thick canopy blocked out the light, and the humidity was suffocating. But by noon, I had topped out in the moss-draped montane forest, a land of lichens and ferns and orchids and graced with sunshine. I sat atop a green-carpeted boulder and breathed.

It was lovely there, but I didn't stay long. I still had orangutans on the brain, and the researchers at the station had promised to alert me if they came across any. They'd warned me not to get my hopes up. Orangutans are the only great apes that don't live in large social groups. Since they rely mainly on fruit, a crowd would quickly exhaust an area's food supply. So they spread out and can range far from the research station. It might take days of searching to find them. My departure loomed, and I was running out of time.

The next morning, I was sipping coffee made candy-sweet with condensed milk, the way locals drink it, when a student hurried to my cabin. A pair of orangutans—a mother and son, known to researchers as Bibi and Bayas—had been spotted a half hour's walk from camp. I shoved my shriveled feet back into perpetually damp socks and boots and grabbed my binoculars.

We found the two apes, with their telltale ginger frizz and bulbous bellies, grazing in the canopy. One by one, they plucked and slurped down Popowia, one of the hundreds of fruits they eat. Feeding is an all-day affair, and the apes will move from tree to tree with ease to find what's ripe. Technically, they're frugivores—an average of 60 percent of their diet is fruit—though they'll also eat tree bark, leaves, and insects. But the fruiting cycles of the trees shape their journeys across the forest. The apes, in turn, help shape the forest, seeding new trees as they poop along their travels.

Apparently unaware of the vital service they provide, mother and son, with their hooded eyes and languid movements, seemed utterly bored with their task. But that was my human bias—perhaps what I was seeing was total orangutan zen. Unlike me, with my previous clunky ascent into the canopy, they casually traveled between trees on those impossibly long arms. Sometimes seven-year-old Bayas would stand on a slender bough and lean out until it bent under his bulk, then ride it to a neighboring trunk. When thunder announced a storm, Bibi, who's estimated to be about 30, displayed her wisdom during a short rain, holding a cluster of leafy limbs over her head like an umbrella. Bayas, a few trees over, just got wet.

I followed their movements until my neck spasmed, until the light dimmed, and with each passing moment, I worried I'd miss something. Finally, Bibi built a nest, as she does most evenings, bending branches to make a platform up high. Bayas joined her, and they settled in for the night.

Before I left Gunung Palung, Endro Setiawan offered to give me a very different kind of tour of the lush world around us. We were walking along a trail when the 43-year-old forester stopped and slid a mandau, the machete-like knife carried by the Indigenous Dayak people, from a sheath at his waist. Using the shining toothed blade, he nicked a bit of bark from a tree, then tapped, exposing the underbark. "Smell that," he said. I pressed my nose against the wound. It smelled ... Earthy? A little sweet. "That is the smell of Dillenia," he said. Then he had me press an ear against the same spot, to hear the tree's song—mildly fizzy, like a lightly sparkling wine.

Here, the soft-spoken Indonesian tree expert was in his happy place, revealing the secrets of the forest he's spent years studying. He and a team of university students from Jakarta and elsewhere were working to identify all the tree species inside 39 research plots for a detailed database. They expected to add hundreds more to the thousand already known. "Plants are the window on the science," he said. "If you know the plants and trees, you know the heart of the park. From there you can learn about everything that relies on them."

The Milky Way comes into view through a gap in the canopy. Borneo's rainforests are millions of years old and among the most biologically diverse on Earth, a resilient home for thousands of species found only there. The hope is that humans allow them to flourish far into the future.

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I examined, listened to, and smelled a host of trees as we walked. Endro pointed out the grand Shorea with its giant buttresses, like the fins on a rocket, that offer stability where underground roots are shallow—common among dipterocarps, the giant hardwood that dominates the forest. Borneo is a hot spot for trees from this family, with some 270 species. He spotted a strangler fig and described how it sprouted from a seed that found purchase in the high crotch of another species, slowly sent roots to the ground, and ultimately choked its host.

He showed me the stump of a Borneo ironwood—a victim of loggers. The evergreen produces a dense, heavy wood locally cherished but prized by builders. This tree, he noted, could have topped 150 feet and lived a thousand years.

Endro explained how every three to five years or so, the forest experiences a phenomenon called mast fruiting, when trees suddenly produce a superabundance of fruit and attract large amounts of wildlife. Though the fruit supply at the moment was modest, fruiting species abounded, including 56 species of fig trees alone.

As we explored, I pestered Endro for the names of the trees we passed. There were Dipterocarpus, and Shorea, Hopea and Vatica, Monocarpia and Melanochyla—an endless stream of Latin names. I gave up trying to remember them all and just followed him, soaking it all in.

The lessons continued, and a pattern emerged: The trees offer nourishment to the orangutans—as well as to the other mammals, birds, reptiles, amphibians, insects, fungi, and microbes—but for many, the trees also provide structure, a calendar of the seasons, a transport system. For others, a playground, a school, shelter. For all, a place to lay their heads. A home.

Days earlier, on that climb into the canopy, I'd hoped the wildness of the place would burst forth in animal form. But now it was obvious I'd been immersed in something more profound—the cradle of everything that lives here. As Endro helped me see: What could be more important, more glorious, than the habitat that makes it all possible?

Longtime contributor Jennifer S. Holland is the author of the book Dog Smart: Life-Changing Lessons in Canine Intelligence, publishing in May.

A field biologist, wildlife photographer, and filmmaker, Tim Laman documents rare and at-risk animals in tropical rainforests. His pioneering research in Borneo's tree canopy led to his first National Geographic feature story, in 1997. Mixing science with photography offers "the best of both worlds," he says. An Explorer since 1991, Laman co-founded the Birds-of-Paradise Project at the Cornell Lab of Ornithology and has earned many awards, including Wildlife Photographer of the Year from London's Natural History Museum.

The nonprofit National Geographic Society, working to conserve Earth's resources, helped fund this article.

This story appears in the February 2024 issue of National Geographic magazine.

These Australian Frogs Get Absolutely Covered In Seeds

John Gould, an amphibian scientist at the University of Newcastle in Australia, had wandered into a dense thicket of vegetation around a pond when he first spotted the fluffy frogs. Frogs are not usually fluffy, so Gould took a closer look and discovered that the frogs were covered in the wispy seeds of Typha orientalis, a common pond plant also known as the broad-leaved cumbungi.

[Related: Check out some of the weirdest warty frogs in North America.]

"It immediately reminded me of a recent science story about a frog that was found to carry pollen on its skin," Gould told PopSci via email. "Which made me think it might be possible for frogs to do the same thing but with seeds."

Plants have evolved many different ways of spreading their seeds around the planet. Some seeds have adapted to float on the wind, some can float through water, and others simply drop on the ground and hope for the best. But one of the most ingenious ways plants spread is through animals. They can coax wildlife to eat fruits containing their seeds or even cover their seeds in bristles that stick to the fur of an animal, who drops those seeds far away.

But while this phenomenon has been widely studied in animals like birds and mammals, this new observation could be one of the first documented instances of seed dispersal in an amphibian.

"I think we often have a simplistic view of the environment and how species interact within these systems," Gould said.

The frogs that Gould spotted were Litoria fallax, or Eastern dwarf tree frogs, a small green species native to Australia's east coast. After the initial spotting, he and his colleague collected some data to investigate how common it was for these tree frogs to end up covered in Typha seeds and published their results on January 3 in the journal Ethology.

Amphibian skin could help disperse Typha seeds that easily stick to the Eastern dwarf tree frog's wet skin. CREDIT: John Gould.

The team found that around 30 percent of the tree frogs at their pond had Typha seeds stuck to them, with seeds found all over their feet, legs, backs, and bellies. Some of these frogs were carrying just one seed, but at least one individual they observed had up to 14 individual seeds all over its body.

Gould said that he believes the frogs probably picked up the seeds by climbing through the thicket of plants where the seeds had fallen. But just because you brush up against something doesn't mean you'll start carrying it around. The Typha seeds seemed to attach themselves to the frogs specifically because the seeds' thin, hair-like tufts can easily stick to the frogs' wet skin. Scientists believe the seeds' wispy tufts evolved to help them catch the wind like a kite—but Gould said that this trait could also come with the secondary, or even unintentional, advantage of attaching the seeds to sticky frog skin.

"One trait may have several benefits, some of which have not been directly selected for but happen to be advantageous," he said.

[Related: This tiny 'leaf-nester' is the smallest known fanged frog.]

Their study notes a couple of instances where amphibians are known to act as seed dispersers, like Izecksohn's Brazilian tree frog, which has been documented carrying the seeds of a couple of different plants after eating their fruit. These examples are rare—most frogs are carnivorous, Gould said, meaning they don't eat fruit and carry seeds around. But the role of amphibians in seed and pollen dispersal may also be understudied, he added.

That being said, it's unclear how important these frogs are to the Typha's seed dispersal—or even whether the frogs contribute to the plant's seed dispersal at all. Just because the seeds stick to the frogs doesn't mean that the frogs often carry them to places where they might sprout into new plants. To study this, researchers could follow seed-covered frogs to see where they bring the seeds and how the seeds fall off, Gould said. Additionally, he added, researchers could place seeds on different frogs and track them that way.

But dispersing their seeds through sticky frog skin might be advantageous to the Typha plants, Gould noted. Seeds carried on the wind are dispersed essentially randomly, wherever the wind happens to take them. But, as he pointed out, frogs might carry those seeds directly to another pond, or some other optimal location where the plants can grow.

Why Do We Say We Have Frogs In Our Throat?

(Last Updated On: January 21, 2024)

If you've ever had a phlegm-ball stuck in your throat and tried to talk anyway, your voice might have come out sounding different than it normally does. One might say you have a frog in your throat. Maybe you're not the one with a frog in your throat, and instead it's the person who showed up to school/work sick and insists they're clearly not sick while getting everyone else sick. Also, don't be that person. But why do we say we have frogs in our throat—of all animals?

Medieval Medicine

When you think about modern medicine you're probably pretty glad you're not subject to medieval medical techniques like bloodletting or the "doing surgery without modern general anesthesia" thing. One such medieval practice involved the use of frogs. Allegedly frogs could cure asthma if you swallowed them. No, we don't know how this was supposed to work and considering that doctors give you an inhaler instead of a frog nowadays probably means it didn't work that well. 

There have been assertions bandied around that frogs in medieval medicine were used to help with sore throats, but all of the ones we could find were related to the idiom "frog in your throat" and how they're not connected at all. 

Frogs are used today as a detox technique by indigenous peoples in South America. It's called kambo, and it's intended to purge toxins from the body by using toxins from the giant monkey frog. These frogs release toxins through their skin when they get stressed out, so kambo first starts with picking an unlucky frog up and stressing the poor bugger out. Then the skin (yours, the one getting detox-ed) is burned a bit and the toxins are scratched in. 

Kambo has been described as both a horrible experience but also one that those who have done it plan to do again, unsurprisingly by rich people from California. 

So is it a medicinal thing at all?

The idiom saw very early use in the 1840s, entering widespread use in the mid 1980s. Our idiom of the day is thought to have its earliest publication in a book by an American clergyman named Harvey Newcomb in 1847. The book was called How to Be a Man and in it he writes the following: 

"Now let me beg of you to learn to say NO. If you find a 'frog in your throat,' which obstructs your utterance, go by yourself, and practise saying no, no, NO!"

The more widespread popularity of the idiom likely emerged with commercial throat lozenges and cough drops. "Frog in your throat?" was a common marketing phrase placed on the boxes of lozenges in the early 20th century.

See if you know your frogs and other amphibians here.

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