The Indonesian island of Sumatra is the only place left on the planet where an astonishing variety of species including elephants, sun bears, clouded leopards, tigers, rhinos and orangutans live together. It is also where an alarming number of these animals are disappearing in the face of oil palm plantations, illegal logging and human encroachment.

Recently, accompanied by wildlife enthusiasts, I led a mission to install camera traps on Dolok Simalalaska, the highest mountain in North Sumatra, to try to survey the state of some of the strangest, rarest, most beautiful and most endangered creatures in the world. They include the Sumatran striped rabbit, Indonesian mountain weasel, Helmeted hornbill, Sunda clouded leopard, and Sumatran tiger—hopefully with cubs.

The purpose of the expedition, which left from Medan, was to determine the presence of rare species and use this evidence to implore the Indonesian government to gazette this landscape as a national park. In the past, I have worked with the Los Angeles-based People Resources And Conservation Foundation and Habitat ID to conduct rapid response surveys to find Sumatran tigers, Malayan tapirs, Sunda clouded leopards, and other species.

This time, we felt that if we could get a recording of a helmeted hornbill, which is listed by the International Union for Conservation of Nature as Critically Endangered, as well as camera trap video footage of Sumatran tiger cubs—another species listed as critically endangered—showing proof of a breeding population, then we could present a strong case to the government. If the presence of two critically endangered species couldn’t win this place some protection, what could?

On that first night we strung up our hammocks in a palm oil plantation near the home of our team leader, local Batak conservationist Haray Munthe. Our noses stung from the pungent odor of ammonia that is mixed in with fertilizer. Mosquitoes swarmed, but we headed down to the nearby river anyway because Mr. Munthe had arranged a welcoming party for us on a sandy beach where his neighbors sang and played traditional songs on acoustic guitars and where tuak or palm wine flowed from plastic bags which we mixed with Bintang Beer.

We awoke to a family of Agile gibbons calling somewhere in the distance. Some scrap of forest must have been spared somewhere in this human-altered landscape, or so I thought. I brought up the gibbons with Mr. Munthe, who quickly dispensed with my idea. He informed me that a single family of Agile gibbons survived in a one-hectare rubber plantation amidst the infinite oil palm fields. That sobered me up. Here we were in Sumatra, a place that a few decades ago would have been second only to the Amazon in species diversity, breaking camp in a palm oil plantation—scourge of the tropics—our noses burning with ammonia, and listening to an endangered species crying out in a wasteland of anthropogenic transformation. I hoped this situation would not become a metaphor for our expedition.

The real journey began with a long ride through the mountains to the put-in place for the Bila River, the main waterway in the mountains south of Lake Toba. With our boatmen paid off we made our way up for Lobu Tayas, with langur monkeys shrieking at us in the surrounding hills, and encountering pitcher plants such as Gymnaphora along way, hanging off the side of the cliff like tropical Christmas ornaments. In the Batak language “lobu” means “abandoned”, so we were headed for the “abandoned village of Tayas.” In fact, every year that I visit more and more families leave this quaintly situated village for Rantau Prabat, joining the throngs of transients searching for work on plantations.

From Lobu Tayas we began the long trek up “Dog Back Mountain,” so called because so steep is the walk on the shade-less ridge line up into higher altitude that even village dogs are known to turn back once they get a sense of what they are in for. It was dark by the time we reached the top, and up on the summit is a farmhouse surrounded by forest and a mixed farm of coffee, areca nuts, mangoes, jackfruit, and other crops. I knew that in the morning, from this high position on the mountain, we would be treated to a wonderful morning Agile gibbon chorus.

In fact, last year from this same spot I woke to the sound of their droopy, almost cartoonish early cackle-like call—which is often how they begin their morning songs—at 4:30 am. A full moon still hung in the black sky amid the stars, lower on the horizon. To hear gibbons calling in the night under a full moon was truly extraordinary. It just doesn’t get any more beautifully exotic than this, I told myself, shaking my head at the majesty of it.

Two days later we reached the top of Dolok Simalalaska—a wet, mossy netherworld at nearly 2,000 meters—where five new camera traps are now deployed. Few people venture to these high peaks, fearful of the orang bunian, the evil spirit of the mountains. It remains a hidden sylvan world of stalagmite-like moss-covered trees and eerie silence.

On the way down I recalled that we could get a phone signal on the trail, and I reminded Raja, our second team leader, to let me know when we came to that spot. He was about 15 meters ahead of me down the trail when I saw him gesticulating and jabbing in the direction of the trees to the left. I thought this was a strange way of telling me that we had found the signal when I realized what he was so enthralled about.

Credit: Arin Nature Photography

Hu…hu…hu…hu….hu…Ka..Ka…Ka..KaKaKaKaKaKaKaKaKaKaKa! It was the helmeted hornbill! The call of the helmeted hornbill is not just enchanting, it is an emissary of the past, an echo from the time when the great trees were kings and tigers, rhinoceros, orangutans and other megafauna swarmed in the thousands, when every morning the mist rose off the boundless tree canopy of the island and Siamangs, Agile gibbons, orangutans, leaf monkeys, seven species of hornbills and countless other birds, insects, amphibians, and mammals set off of chorus that created the greatest cacophonous melody the natural world has ever produced.

And here we were listening to one of the last of its kind, the lone helmeted hornbill of the mountain, the one that got away from the poachers, due to luck, weather, bad aim, whatever. We remained in that spot for nearly an hour and it called again. Perhaps it was saying goodbye. It was getting late in the afternoon, and we decided to move on. I marked the spot on my GPS: Helmeted Hornbill.

We were now one crucial step closer to getting this landscape protected. We’ll be going back for the camera traps at the end of the year.

Gregory McCann is the Project Coordinator for Habitat ID and the author of the book Called Away by a Mountain Spirit: Journeys to the Green Corridor. You can support his conservation projects in Sumatra and Cambodia here. paypal.me/GregoryMcCann