India and Nepal Are Building the World's Largest Transboundary Tiger Conservation Zone in the Terai

The Terai Arc Landscape is a 49,000-square-kilometre belt of grassland, riverine forest, and sal woodland running along the base of the Himalayas, from India's Uttarakhand in the west through Bihar and Uttar Pradesh, crossing into Nepal's lowland Terai districts and back. It holds eleven protected areas on the Indian side and three major national parks in Nepal, including Chitwan and Bardia. WWF identified it in 1997 as one of the planet's most critical tiger habitats, not because it was pristine, but because enough of it remained connected to be worth fighting for.
The Bengal tiger (Panthera tigris tigris) needs enormous home ranges. A single adult male can patrol 60 to 100 square kilometres. Females require 20 to 60. When forests are fragmented into isolated pockets, tigers cannot find mates, gene pools collapse, and local populations quietly disappear within two or three generations. The Terai Arc works because it keeps those pockets joined.
India's 2022 tiger census counted 3,167 tigers, up from 1,411 in 2006, when Project Tiger's failures were still being tallied in the press. Nepal's count, conducted using camera traps across the Terai, recorded 355 tigers in 2022, a near-tripling from the 121 counted in 2009. Both governments cite transboundary movement as a direct factor in the recovery. Tigers tagged in India's Valmiki Tiger Reserve have been photographed inside Nepal's Parsa National Park. The corridor between Dudhwa in Uttar Pradesh and Bardia in Nepal is now considered a single functional habitat by wildlife biologists, even though it crosses an international border.
The biological mechanism is straightforward. A tiger born in Chitwan that disperses west into Bardia, then crosses into Katerniaghat Wildlife Sanctuary in Uttar Pradesh, carries genetic material across three protected areas. That movement prevents inbreeding depression, the decline in fitness that occurs when a small, isolated population breeds within itself over successive generations. The Terai Arc makes that movement possible. Removing any one link in the corridor breaks the chain for every animal that uses it.

The formal architecture is the Treaty of Peace and Friendship between India and Nepal, supplemented by bilateral wildlife agreements signed in 2009 and renewed since. On the ground, it works through joint anti-poaching patrols along the open border, shared camera trap databases, and coordinated elephant corridors, because elephants, like tigers, do not read boundary markers.
The Indian Forest Service and Nepal's Department of National Parks and Wildlife Conservation run a joint monitoring programme across the Susta-Valmiki corridor. Rangers from both sides share intelligence on poaching networks, which historically exploited the border's openness to move tiger parts from Nepal into India and onward to Chinese markets via the northeast. The 2022 TRAFFIC report on tiger trade found that coordinated cross-border enforcement had reduced seizures of tiger bones and skins along this specific corridor by a measurable margin compared to the 2010s, a sign the intelligence-sharing is doing real work.

Three pressures sit outside the reach of any bilateral agreement. The first is infrastructure. The proposed Gorakhpur-Nautanwa rail expansion and several highway widening projects in Uttar Pradesh cut directly through wildlife corridors identified in the Terai Arc management plan. Underpasses and overpasses for wildlife have been built on some stretches, the NH-27 crossing near Dudhwa has documented tiger crossings, but the pace of construction outstrips the pace of mitigation planning.
The second pressure is human settlement along the buffer zones. Communities in the Terai's forest fringe depend on firewood, grazing land, and seasonal cultivation inside buffer areas. Conflict between tigers and livestock, and occasionally people, is not a fringe event. The National Tiger Conservation Authority recorded 125 human deaths from tiger attacks across India between 2014 and 2021, with the Terai reserves accounting for a significant share. Conservation that ignores this arithmetic does not last.

The third is climate. The Terai's grasslands depend on monsoon flooding cycles to remain open habitat. As Himalayan glaciers retreat and river flow patterns shift, the tall elephant grass that tigers use for cover and prey species depend on for grazing is changing in ways that models have not fully captured.
The Terai Arc is the largest transboundary conservation effort in Asia by area, and one of the few in the world where tiger populations on both sides of the border are simultaneously recovering. What makes it worth studying is not the tiger count alone. The reserve model here has produced measurable co-benefits: greater one-horned rhinoceros numbers in Chitwan and Dudhwa, recovering gharial populations in the Gandak and Girwa rivers, and Gangetic dolphin sightings increasing in the Karnali. A corridor built for one apex predator ends up carrying the whole food web.
The tiger in the Terai is not a symbol of anything. It is a large, territorial mammal that eats deer, drinks from specific rivers, and requires more space than most Indian cities allow. The fact that two countries with a complicated shared history have managed to keep that space functional, not perfectly, but consistently, is the actual story the numbers are telling.