A male northern white-cheeked gibbon (left) and a mother carrying her baby hang out in a treetop in Vietnam's Pu Mat National Park in a recent picture.
The animals are part of a newfound population of more than 400 of the gibbons, which are deemed critically endangered in Vietnam and Laos by the International Union for Conservation of Nature. The gibbons, which have declined due to widespread hunting and logging of their habitat, are likely extinct in China.
Conservation International had been searching for the rare primates since 2008, finding only a few scattered groups—until now. New auditory sampling surveys—during which researchers record the calls of gibbon "families"—have revealed that Pu Mat is home to 130 gibbon groups, for an overall population of roughly 455 individuals.
The discovery of such a large gibbon population may mean the species has a better chance of long-term survival, the scientists say.
Lone male gibbons—like the one pictured—make solo calls as they roam widely in search of a mate. The male's song is one of two types of calls recorded by researchers working in Pu Mat National Park, primatologist Luu Tuong Bach said via email.
The other call type is a duet between the male and female, sung once they've settled into a lifelong, monogamous bond, according to Luu, a Conservational International consultant who led the field surveys in Vietnam.
"The northern white-cheeked gibbon is a highly territorial species, so if they mate together to make a family and you hear them this morning, the next day you may hear them in the same area, or very close," Luu said.
Gibbons are among the 6 percent of primates that mate for life (pictured, a female gibbon grooms a male).
The new northern white-cheeked gibbon population in Pu Mat was found in dense, high-altitude forests far from human settlements. But new roads through the region are being planned to increase border patrols between Vietnam and Laos—which may also increase access for poachers or loggers.
Luu said poachers typically hunt the animals for food or shoot mother gibbons to capture the infants to be sold as pets. The animals' body parts may also be used in traditional medicines, according to IUCN.
Northern white-cheeked gibbons have specialized wrist joints and powerful arm muscles, which allow them to swing from tree branches, like the male pictured above in Pu Mat. The primates eat fruit, leaves, and insects and rarely descend to the ground.
While the newly discovered group—if properly protected—is enough to ensure the long-term survival of the species, gun control is also vital, Luu said.
"Without direct protection in Pu Mat National Park, it is likely that Vietnam will lose this species in the near future."