Mondulkiri looks nothing like the rest of Cambodia. It is rolling grass hills, stands of pine, red-earth roads and a plateau close to 800 metres, and it is the country's largest province and its emptiest, with about six people to the square kilometre. Eight in ten residents belong to indigenous minorities, most of them Bunong, whose families kept working elephants for generations. The forest on the southern edge is the reason most people come. Keo Seima Wildlife Sanctuary, 2,900 square kilometres, holds roughly 1,400 southern yellow-cheeked crested gibbons and around a hundred wild elephants, among Cambodia's last. It also holds almost every black-shanked douc left on Earth: some 25,000 blue-faced monkeys with lower legs that look dipped in black, against about 500 across the border in Vietnam.
You meet the animals here on their terms. At the Elephant Valley Project, started in 2006 in forest beside the sanctuary, the rule is no rides and no tricks: you keep six to ten metres back and follow rescued elephants while they graze, bathe and doze. At Jahoo, a camp the Bunong of Andoung Kraloeng run with conservation biologists, you leave in the dark and find the world's only habituated groups of yellow-cheeked crested gibbons by the sound they make at first light. East of Sen Monorom, the Bou Sra river drops into the jungle in three steps, a trickle in March and a roar at the end of the monsoon. None of it is untouched: rubber concessions and logging stripped more than 20,000 hectares from Keo Seima between 2010 and 2014, and what stands today stands because it is patrolled. The doucs, at least, have held steady through the decade.