We lurched along an unpaved road in the night, walls of trees and knotted vines on either side. In the darkness lurked some of the world’s most unusual mammals, and I had come to Borneo to fulfill a lifelong dream to see them: catlike civets, scaled anteaters called pangolins and big-eyed colugos that spread their body flat as they glide from trunk to trunk.

In the open back of a pickup truck, two wildlife spotters stood in front of me, whirling their flashlights. To my right stood my father, whose lifelong obsession with wildlife had inspired my own. Clothes damp from the humidity, we plunged deeper into the moonlit jungle.

My father and I had long wanted to travel to Borneo together, inspired by an online community of people called mammal watchers, who shared tantalizing stories about their sightings on the island on the website mammalwatching.com.

Mammal watching is superficially similar to bird-watching: trying to see as many wild species as possible. It is hard — mammals can be elusive — but rewarding, as the most interesting mammals dwell in the Earth’s wildest and most vulnerable places. Searching for these creatures is both an adventure and an exercise in supporting conservation.

So much of my interaction with mammal watching had been virtual that, on a warm June night, as we rumbled through the 140,000-acre Deramakot Forest Reserve in the Malaysian state of Sabah, I could hardly believe what I was seeing.

A flashlight caught a gleam on a branch to the left. We trained our flashlights about 50 feet up a fig tree to see a binturong, a blackish gray, shaggy, whiskered creature also known as a bearcat.

This was one of the creatures that had been living in my imagination since I was a child, and I felt an electric thrill.

Endangered Eden

The island is home to some of the most iconic, and unusual, mammals on Earth, species like orangutans, pygmy elephants and proboscis monkeys with their bulbous noses.

“It had a mystique that was larger than life,” said my father, who read about these animals as a child growing up in India.

Until a few decades ago, Borneo was covered in tropical forests. Then, in the early 1970s and the decades after, many forests were logged and cleared for palm oil plantations, until more than one-fifth of the total area of Sabah was planted with oil palms, according to a 2022 study published in the journal Land Use Policy.

Bornean wildlife paid the price. The population of Bornean orangutans, found nowhere else in the world, declined by more than 50% over the last 60 years, according to the World Wildlife Fund, a conservation nonprofit.

With a sense of urgency, my father and I planned a trip for last June with the help of Jon Hall, the founder of mammalwatching.com and the de facto leader of the mammal-watching community. We ended up with an itinerary that included Deramakot, the majestic Kinabatangan River and some of the oldest rainforests in the world in Danum Valley.

An outfit called Adventure Alternative Borneo offered a relatively affordable price for a mouthwatering 10-day itinerary: $2,950 each, not including airfare.

Serenaded by cicadas

The Bornean jungle felt intensely alive.

There was the daily chatter of cicadas, a different buzz going off every few hours; the so-called 6 p.m. cicada sounded like a saw screeching against metal. Everything was always wet, drenched by daily downpours and humidity so heavy it made gulps of air feel like full glasses of water. Sinuous vines, mosses and fungi — some looking like luminescent teacups, others like miniature red lava lamps — grew anywhere there was space.

After landing in Sandakan, a city of nearly 200,000 in the island’s northeast, we met our guide, Lister Johns, a native Bornean, who drove us about 20 minutes to a town called Sepilok. We stayed at the Sepilok Forest Edge Resort, a modest lodge with an open-air cafeteria, a few chalets and a glamping area. Orangutans, gibbons and monkeys were said to cruise through the trees on the property, and the roof to our small room was home to short-nosed fruit bats.

At the nearby Rainforest Discovery Center, a network of suspended walkways brought us into the canopy, where a large orangutan came crashing through branches and leaves and observed us from a treetop. In the evening, red giant flying squirrels sailed from trunk to trunk in the twilight.

But we knew Sepilok was just an appetizer compared with our next destination, Deramakot, about 60 miles to the southwest. This was where others posting on the mammal-watching website reported seeing some of the rarest wildlife, including tree-dwelling clouded leopards and sun bears, the smallest species of bear in the world.

There was only one place to stay in Deramakot, arranged through tour companies: a station of the Sabah Forestry Department, which offered a few guesthouses with spartan rooms that had an air conditioner, a pair of twin beds and not much more. Forestry department staff members cooked meals for guests. The station’s seclusion made it a perfect launchpad to explore the forest at night.

Deramakot delivered: On two of our five nights there, we set out after dinner for six-hour drives, finding not only binturongs, but several leopard cats and slow lorises, venomous primates that look like yellow teddy bears. During the day, we spotted red leaf monkeys, a family of orangutans and a pygmy elephant.

My dad was ecstatic. “The fact that these nocturnal creatures that live high up in the tropical rainforest, it’s possible to actually see them so well — to me that was one of the mind-blowing parts,” he said. “I used to drool over these pictures in the book on wildlife in India.”

Ancient wilderness

I felt the most intimate connection with Borneo at our last — and wildest — destination, the Danum Valley, which teemed with rainforests that are, by some estimates, 130 million years old, among the most ancient in the world. The jungles there were relatively undisturbed, with liana vines twisting and spiraling through towering trees.

The humidity dampened everything. We spent three nights at a nearby property called Infapro, which had a cafe and some guesthouses. From there, we drove every day to the main Danum Valley field center to hike in the jungle.

One day, we came across a family of Bornean gibbons, endangered apes that swing impressively from branch to branch using their extremely long arms and legs.

Over just 10 days in Borneo, we saw nearly 40 mammal species, as well as almost 200 species of birds, venomous snakes, freshwater crabs and more. We left the island exhausted and in disbelief at how much our senses had taken in.

But both of us are only getting started.

“Absolutely not done,” my dad said. For our next mammal-watching adventure, he’s already dreaming about the tropical forests of West Africa.