Four orangutans were released into the wild on Indonesia's Borneo island on Tuesday, an official said, as the country ramps up efforts to protect the animals from extinction.
They were the first among 40 orangutans planned to be released by the end of the year, Mega Hariyanto, the forestry ministry's conservation chief for Central Kalimantan province, told AFP.
"The orangutans were flown from the rehabilitation centre to a town near the Bukit Batikap forest on Monday. A team of vets took them to the forest this morning by helicopter," he said.
The release was a collaborative effort between the Forestry Ministry and non-profit organisation Borneo Orangutan Survival (BOS) Foundation, Hariyanto said.
"There are still more than 600 individual orangutans at the Central Kalimantan Orangutan Reintroduction Project who are waiting to be released back to their natural habitat," the organisation said in a press statement.
A dozen more orangutans are expected to be set free by end of next month, it added.
Experts say there are about 50,000 to 60,000 orangutans left in the wild, 80 percent of them in Indonesia and the rest in Malaysia.
They are faced with extinction from poaching and the rapid destruction of their forest habitat, driven largely by palm oil and paper plantations.
Conservationists in the region have been raising awareness about the plight of the endangered primates in various ways.
"Born to be Wild", a documentary by Warner Bros and IMAX which has been screening worldwide since last year, shows primate expert and Orangutan Foundation International founder Birute Mary Galdikas rescue, rehabilitate and return orphaned orangutans into the wild.
The film's producers last week screened the film in the jungle where, according to the crew, at least four orangutans watched themselves on screen.
"Their reaction was great. Orangutans have short attention span and it is incredible to have them sit 10 to 15 minutes to watch the movie," crew member Frederick Galdikas said.
Explore further: The influence of the Isthmus of Panama in the evolution of freshwater shrimps in America