Elephants have joined the front line in the fight against poaching and illegal logging in the dense jungles of Sumatra.
Guided by their Indonesian mahouts, they trek alongside rivers, over rough terrain and deep into the rainforest in an area that is home to numerous endangered species, from orangutans to tigers, but which has suffered devastating deforestation in recent years.
The sprawling archipelago has large swathes of tropical forest but vast tracts are being felled to make way for palm oil and pulp and paper plantations, destroying biodiverse habitats and adding to greenhouse gas emissions.
Much of the logging that takes place is illegal as it happens outside concessions granted to companies, but it is hard for authorities to keep track. Poaching of endangered species is also common, with elephants killed for their ivory and tigers for their pelts.
The elephant patrol project, run with communities in the Trumon district of Aceh province, on Sumatra island, aims to give a helping hand.
It employs local men as "mahouts", or elephant-keepers, who keep a lookout for illegal logging and poaching and report it to authorities to follow up.
Hendra Masrijal, 33, quit his job as a food vendor to become a mahout. He is among a group of around about 25 keepers involved in the scheme, including former separatists who fought against the central government until a peace deal was struck a decade ago.
"It makes me sad when I see pictures of elephants killed by poachers for their tusks," Masrijal told AFP. "Their habitat is also being encroached (on) by farmers and villagers."
The patrols deep into the jungle last between two and seven days, with mahouts normally spending 15 to 20 days a month on expeditions.
The initiative covers a vast area of 27,000 hectares (66,700 acres) called the "Trumon Wildlife Corridor", which is wedged between two conservation areas. Authorities are currently trying to push through legislation to give it protected status.
As well as keeping a watch for logging and poaching, the programme has staff who conduct training in local communities and develop eco-tourism to give villagers who have traditionally lived off illegal practices an alternative livelihood.
Tisna Nando, a spokeswoman for USAID, which has funded the expansion of the project over the past year, said communities were "enthusiastic" about the initiative.
"They see that they can actually benefit economically from protecting the forest in the area, rather than cutting it down," she told AFP.
A study last year published in the journal Nature Climate Change showed that Indonesia had for the first time surpassed Brazil in its rate of tropical forest clearance, despite a moratorium on new logging permits imposed several years ago.