Primates released into the forest near Angkor Wat after years in captivity have started to display natural behaviours, which are vital if they are to survive in the wild, according to the animal charity responsible for their reintroduction to the area.

Nick Marx, director of Wildlife Alliance, said that two pairs of gibbons, one of which has had a baby, and three langur monkeys, who now roam freely in some of Cambodia’s oldest forest, have started to shed the habits of incarceration.

“The gibbons and the langurs are behaving more like wild animals because they are moving around independently and foraging for food, which they didn’t have the opportunity to do in captivity,” he said “The male gibbons are protective of their family and sometimes hostile if humans get close, but that is good, because it’s natural behaviour.”

The gibbon couples were also singing duets and mating, bonding behaviour which is a must if they are to sustain a new life in an area devoid of other gibbons, Marx added.

The first pair of gibbons was reintroduced in 2013 to the archaeological park, an area almost entirely stripped of wildlife by overhunting. Like a second pair of gibbons, and the three langurs, introduced a year later, the couple started their new forest life in a secure enclosure.

“The enclosure has branches and we feed them natural leaves and fruits from the forest to get them used to the local diet,” Marx said. “When you open the door, you hope they are equipped well enough to survive on their own.”

The animals quickly moved away from the enclosure and are relying less and less on food Wildlife Alliance provides.

“The first pair stopped taking the supplementary food after three days, and they moved away from the immediate area,” Marx said. “For six months they didn’t need any of the food we put out.”

But snap-happy tourists and enterprising tuk-tuk and motodop drivers started luring the gibbons down from trees with unhealthy snacks, threatening to undermine the re-wilding process.

“We had to use extra food to lure the animals deeper into the forest to get them away from curious humans,” Marx said.

The arrival of the second pair of gibbons encouraged the langurs to move further into the forest, too.

“When we released the second pair of gibbons, the male became territorial and chased the langurs from their enclosure that was nearby,” Marx said.

Both pileated gibbons and Germain’s silver langurs are endangered, according to the IUCN red list of threatened species. Their reintroduction to Angkor has been achieved through a partnership between Wildlife Alliance, the Apsara Authority and the Cambodian Forestry Administration.