There are thought to be only 23 Hainan black-crested gibbons left, and they’re only found on Hainan Island in South China.
There used to be more than 2,000 gibbons there in the 1950s, but logging has devastated their lowland habitat, and the apes have had to move into the highland rainforest to survive.
They’ve also been poached because gibbon bones are valuable in traditional medicine.
In this video, we see the reserve watchmen monitoring the tiny population of primates to see how they’re faring. It’s difficult to spot the animals, but they can be located using their territorial calls early in the morning.
You can hear what the gibbon dawn chorus sounds like at about 1’45. It’s surprisingly similar to bird calls.