Natural curiosity

The gibbons spend most of their time living in the treetops, swinging through forests with their forelimbs, and rarely spend any time on the ground.

"We need to observe the gibbon from 5 am to 5 pm, and record its behavior every five minutes," she says. "In each month we need to observe at least six full days, and we have to keep observing the same gibbon family for years."

There is another challenge -researchers have to take one to two years to let gibbons get used to them being around so that they can record their natural behavior.

According to Yan, gibbons can recognize themselves in the mirror and they have the level of intelligence of a five-year-old child.

"Because they live on the trees throughout the year, they have to learn survival skills for three to five years from their moms to tell which plant can be eaten as food or what kind of branch they can grab that will hold them without breaking," she says.

Yan says when scientists did field study in Yunnan in 1970s, they could still hear gibbons singing around, and she hopes in the future, people can hear the skywalkers' wonderful songs again.