“My heart hurts if I look up,” Arjun said.

No one was paying him much attention. Arjun Rai, 19, is the youngest member of our team. The rope was up and Khem and Tali were busy getting the equipment ready as Rohit climbed into his harness.

“Is it a steady or a throbbing pain?” I asked him.

He took a moment to consider. “Throbbing.”

“Is it like what you feel when you’re really sad sometimes?” I asked, taking a chance.

The pause this time was longer, and he turned to me with a smile. “Yes, exactly like that.”

That’s fear, I was going to tell him. I feel it every time before I go up. But then I thought it best to double-check.

“When you look up at the tree we’re about to climb or any tree?” I asked.

“No, just to look up. Even if I just turn my head up.”

“Well, that’s just heartburn,” I said, readying my own harness.

Butterflies in the stomach is too dainty a euphemism for what happens just before I begin a climb. My gut wants to turn inside out and leave my frame, one way or the other. My hands shake so much that I avoid taking things from people or handing things to them lest they notice. I have to force my steps to be steady as I cradle the slings and foot-loops hanging from my harness to go check the anchor one last time.

I’ve had a fear of heights for as long as I can remember. Growing up in Punjab – where the land is flat as far as the eye can see – I first discovered it on a trip to some relatives’ place in the village. It was a single-storied mud-walled house. You could climb onto the terrace using a bamboo ladder leaning against one wall. Going up was easy. However, the lovely terrace had no parapet and I stayed close to the middle of it. When it was time to go down, I just couldn’t figure out how to get onto the ladder again. I must have been no more than six at the time.

And here I was, about to climb 20 m into a tree on a single 11-mm rope that we’d just finished installing. It was to help Rohit Naniwadekar of the Nature Conservation Foundation (NCF) and his team install an artificial nest box for hornbills in the Pakke Tiger Reserve, Arunachal Pradesh.

Hornbills nest in tree cavities. They can’t make these cavities themselves, so they look for hollows in large trees made by natural causes – where a branch breaks off the main trunk, for example, or for woodpecker holes that have enlarged over time. These cavities are as important as food and are thought to be able to limit hornbill populations. In forests that have been logged in the past, the density of large trees can be low, forcing hornbills to venture outward in search of suitable cavities in areas with considerably higher disturbance, often at the risk of being hunted.

In Pakke, we’d seen oriental pied, wreathed and great hornbills nesting in the reserve forest outside the tiger reserve. Now, we were installing three nest boxes with similarly sized cavities but with openings of different sizes in an area of with a large number of fruit trees inside the tiger reserve, where we regularly encountered hornbills. We were going to check if the cavities were indeed a limiting resource. If yes, and if the nests passed muster, we’d have buyers soon.

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This project was part of the NCF’s Eastern Himalaya Programme headed by Aparajita Datta, who has been involved in research and conservation in Arunachal Pradesh since 1995. The primary focus of her work has been hornbills. As part of a collaboration between the NCF and the Thailand Hornbill Project, some researchers from Thailand who had been climbing trees for the last two decades were to train the team at Pakke. Over 10 days, they conducted intense hands-on sessions, and the rest was learnt on the job.

Ten days is enough time to learn to climb but not enough to overcome your fears. No one knows this better than Tali. Short and of solid build, 31-year-old Tali Nabum is Nyishi, one of the many tribes of Arunachal Pradesh. He is ace at managing all sorts of ropes, lines and cords, and has an instinctive knack for disentangling the most formidable knots. Disposed to unfaltering cheerfulness, he is always full of wit and humour – except when he has to climb. Then he goes all quiet. He probably just hasn’t had enough time to overcome his fears yet.

We climb trees using the single-rope technique: using two ascenders – one attached to the feet and one to the chest – we crawl up like a looper caterpillar or, more relatably, a leech.

Tali’s body begins to stiffen and his steps become smaller the higher he goes. It’s worse if he is any distance away from the tree and can’t use his feet against the trunk to steady himself when the rope swings or begins to turn. Then he’s liable to ball up and cling to the rope. As Khem likes to put it, “He goes slow loris.”

Khem Thapa is 44 and is probably the best climber on the team. He has been with the programme for nearly a decade now. He is smart, meticulous and quick on his feet. Two months ago, however, he hurt his right thigh in an accident, so he couldn’t climb this year. And so it was that Rohit and I climbed to fit three artificial nest boxes.

Putting up each box – resembling a large fibreglass beer barrel about five feet high and weighing about 15 kg – is quite straightforward. Rohit and I climb up and install a pulley on a suitable branch so that the ground team can hoist the nest, with four properly inserted steel cables. Then we secure the cables two around the branch above and two around the main trunk of the tree using U-clamps. Of course, everything takes much longer than you’d expect when you’re dangling in a harness 20 meters above the ground. But we did okay – especially because our ground team worked flawlessly.

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I learnt most of my climbing during three mountaineering courses I took. That’s also where I learnt to overcome my fear of heights. Because the techniques and most of the equipment are the same, Rohit had invited me to help him with the project.

I’ve been visiting Pakke for the last five years on various projects, so working there is like working with family, especially if Rohit is around. We’ve all spent so much time together by now that not only do we have a shared language – a simplified Hindi with a smattering of Assamese phrases – but also oblique references that no one else would understand.

This atmosphere of work – where we’re always serious and yet always ready to burst out laughing – brought out the best in all of us. It was like what Bruce Banner said as he turned into the Hulk: “My secret is that I’m always angry”. In our case, we were always cracking jokes, but forgetting not for a moment the gravity of our enterprise or what was at stake.

Apart from installing the artificial nest boxes, we also climbed up to the natural nest cavities to check, measure and – if required – repair them. A suitable cavity is one that has a mouth just big enough for the female to squeeze into because that way she becomes the biggest animal that can enter that particular cavity. We had data from already occupied nests to know the preferred hole sizes. For example, a great hornbill is more than a metre long from beak to tail and has a wingspan of a meter and a half. But it can squeeze into an opening just 11 cm across!

Inside, the cavities are usually spacious, with high domed ceilings almost always more than a meter high. The bottoms, however, are level with the base of the opening. That way it’s easier for the female to defecate out of the hole – which is what they do – and for the male to feed her. More importantly, however, the female needs a base to stand on when squeezing out of the tight hole, so cavities that are too deep could seem foreboding.

We repaired cavities that had been occupied in the past but hadn’t been used in the last few years. Rohit and I raised the floor by putting in soil, chiseling the opening a bit or both. While we could choose where to put up the nest boxes, the natural cavities were always in far more challenging places.

On our last day of climbing, we had gone to check on a great hornbill nest close to Dumsi Nala that had been used regularly until about two years ago. The cavity was 30 meters up, just below a fork in a 40-meter tall Tetrameles nudiflora. The branches overhead went every which way so all of us had to circle the tree twice, through the thick undergrowth, before we got the whole picture.

The nest had been active for many years. There was a thriving young forest of the hornbill’s preferred food-trees below, and lianas blanketed the main trunk. With nests like this, climbing is the easy part.

The first decision we make is about which branch to get the rope over so that it gets you to the cavity while also being reasonably safe. I trust Khem’s, Tali’s and Rohit’s decisions on this completely. Khem shoots the fishing line with a catapult. If it works, we shake hands and get going. If not, Rohit readies the bow-and-arrow, which has a longer range, and its own set of superstitions. The fishing line then pulls a black twine which pulls a plastic rope which pulls the climbing rope.

Once the rope is in place and safely anchored to a nearby tree, Tali and Arjun hang from it to check and shouts of “okay round” go around. I recheck the anchor and walk up to the rope for Khem and Tali to check me one last time. They will continue to guide me from the ground. I fold my hands, bow to the tree and say Kha pun khap – greetings in Thai, in reverence and humility – and am ready to climb.

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The trunk of that massive Tetrameles I climbed on the last day leaned ever so slightly sideways, so that the rope hung over space and I had to pull myself in using the lianas clinging to it. We have a small piton shaped like a large screw with a solid ring for a head that can be driven into the trunk and used as a secondary anchor. I used one of these to bring me close to the mouth of the cavity and then positioned myself to work on it.

The mouth had a thick stem of the liana going right across, effectively blocking the entrance. I cut this away and chiseled the opening slightly wider. The floor, strewn with large wooden chips and flakes, was almost level with the bottom of the opening and didn’t need any work.

There’s a thin line attached through a pulley to the harness so the climber is always connected to the support team – with equipment, camera and water passing in between them. When everything was done, I took pictures of the nest and panorama shots of the view and sent the camera down with the equipment. Then I took a long moment to take in the view myself.

It was a clear, warm day with a brilliant, hard sky. I was high above the canopy and my gaze skimmed over the tops of the trees to the open expanse of the river, a meandering ribbon of bright blue among the golden-green grasses, to the undulating hills beyond which we usually don’t see when walking in the forest. The hills, draped in forests like fleece, receded into the distance, going gradually bluer, as if the colour of the sky was leaching into them. From up there, the world seemed boundless and inviolable. Peaceful. Everyone below was looking at photographs of the same view right then.

As I removed my piton and prepared to descend, I had the distinct feeling that something profound had occurred, like the sense of a connection established. This showed in everyone’s eyes as well when I came down, and in the conversations we shared later. That day, a tryst had been made, and we had all left a small bit of our hearts riveted up there next to the nest.

In Sufi literature, birha is a word used to describe ‘longing’. It seamlessly unites the pangs of separation – with the attendant anxiety and the heartache – with patient hope. It is with such longing that I look forward to news of the nest that we repaired that day. I long to hear from the team at Pakke that the nest is occupied again, for only then will our work be done, and only then will we find closure.

When that happens, we’ll know the view that the hornbills see when they look out from the nest.

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In real life, happy endings are rare. We had repaired the last nest on January 9 and had moved on to survey the Mahananda wildlife sanctuary in North Bengal. From there, we went to Manas, where the season’s fieldwork came to a close and we returned to Bangalore. The hornbills’ breeding season began then and we waited for news.

On March 27, I received a call from Rohit, who’d been visiting his wife at the Natural History Museum in London.

“Why are you making an international call?” I asked after I realised it was him.

“This was important,” he said, and I knew from his voice that though he was moved, it wasn’t something bad. “I just heard from Pakke.”

The Dumsi Nala nest is occupied.

Sartaj Ghuman is a wildlife biologist and freelance writer.