Namdapha National Park

Listen first. Somewhere above you, a long rising call rolls through the canopy. It is a whooping, echoing song that seems to come from every direction at once. Underfoot, the trail is soft and damp, layered with fallen leaves. The air smells of wet bark, river stone and green growth. Light reaches the ground only in thin, moving patches. This is Namdapha National Park, in the far eastern corner of India, and the forest is already talking.

That call, if you were lucky enough to hear it, most likely came from a hoolock gibbon. Gibbons are apes, not monkeys. They have no tail, they swing through the trees with long arms, and families sing together in the morning to mark their territory. Here is the first surprise. The hoolock gibbon is the only ape species found in India. This forest is one of the places where its song still carries every dawn.

Namdapha lies in the Changlang district of Arunachal Pradesh. This is the state that sits on India's northeastern edge, close to the borders with Myanmar and China. The area was declared a national park in 1983. In the same year it also became a tiger reserve under Project Tiger, India's national programme to protect its tigers. It covers close to two thousand square kilometres. Very little of that area is reached by any road.

The park takes its name from the Namdapha River. The river begins high on the slopes of a peak called Dapha Bum and runs down to meet the larger Noa-Dihing River. The Noa-Dihing is the river you are most likely to see. Its wide bed of grey pebbles and clear, fast water cuts through the forest. Many visitors first understand the scale of this place standing on its banks.

Now for the second surprise — the height. Inside this one protected area, the land rises from low river valleys only a couple of hundred metres above sea level to snowy ridges well over four thousand metres high. That huge range means the forest changes completely as you climb. Tropical rainforest gives way to broadleaf and pine woods. Higher still come rhododendron thickets, alpine meadows and finally permanent snow.

Because of that range, Namdapha is often described as the only park in the world known to hold four kinds of big cat. These are the tiger, the common leopard, the clouded leopard, and the snow leopard. Each lives at a different level, from the warm lowlands to the cold peaks. You are very unlikely to see any of them. These are shy animals in thick cover. But knowing they share this forest changes how a quiet trail feels.

Look up at the tallest trees around you. In the lowland forest, giant trees called hollong grow straight and pale. Their trunks rise a long way before the first branches appear. Climbing plants, ferns and orchids cover the lower trunks. Lianas, which are thick woody vines, hang down like ropes. In this wet, warm climate, almost every surface carries some other living thing. Even a single fallen log becomes a garden of moss and fungus.

The forest is also home to many hundreds of bird species. Hornbills are the ones that stop people in their tracks. You often hear them before you see them. Their heavy wings make a loud whooshing sound as they fly over the canopy, almost like a steam engine. Watch the river edges, too. Kingfishers, forktails and other small birds work the rocks and shallows, flicking from stone to stone.

Some residents of Namdapha are almost legends. One is the Namdapha flying squirrel. It was described by scientists from a single specimen collected here, and it has been recorded very rarely since. It may live only in this valley. Nobody can promise you a sighting. Still, it is a good reminder of how much this forest keeps hidden, even from the scientists who study it for years.

People live here too. Several communities have homes in and around the park, including the Lisu, the Tangsa, the Singpho and the Chakma peoples. Each has its own language, dress and ways of farming and building. Some Lisu villages lie deep along the old track beyond the park's eastern side, many days' walk from the nearest town. Their lives and the life of the forest are closely tied together.

Most journeys into the park begin at the small town of Miao, on the edge of the forest. From there, a rough road and then foot trails lead in. A common base is Deban, a forest camp above the Noa-Dihing. From Deban, guided walks follow the river and climb into the trees. In the wet months, the trails become muddy and leeches are common. In the drier season, the walking is easier, and the river runs lower and clearer.

This is not a place for rushing. A good day in Namdapha is measured in small moments. A troop of macaques crosses a branch. Butterflies gather on wet sand by the river. Fresh pugmarks, the footprints of a large cat, appear in the mud. A patch of mist slowly lifts off the hills. The forest rewards patience and silence far more than distance covered. Local guides know where to stop, and when to stay still.

Before you move on, take a moment where you stand. Notice the layers of green above you, and the sound of moving water somewhere below. Listen again for birds, for insects, for that distant song. As you walk away, look down at the mud for prints, and up at the canopy for movement. You are leaving one of the wildest forests left in Asia — and most of it, you will never see.