Accurate method

"It's a unique and highly accurate method of studying gibbons," said Jiang Xuelong, a professor with the Kunming Institute of Zoology at the Chinese Academy of Sciences.

Having studied mammal ecology and evolution for many years, Jiang said gibbons move very quickly in the forest, swinging from tree to tree.

"They spend their lives in the upper branches of the trees and seldom stay on the ground. That makes observation a challenge," he said.

Physical fitness is crucial for the job, and the process of recording the animals' movements scientifically is also demanding.

According to Li, the gibbons' movements must be recorded every three minutes. The recording schedule usually only ends at about 7:30 pm, when the animals make their final choice of a tree in which they will spend the night in safety.

"During the day, they only have a nap at noon. So, we have to walk for about 13 hours a day in the mountains. It's a tough job, even for a young man. On rainy days, the work of observing and recording is even harder than usual," he said.

Having persisted in his efforts for two years, Li successfully drew near the three gibbon groups at Chamagudao station. In 2013, he saw them for 19 consecutive days during each of his monthly 22-day patrols.

Now, the distance between him and the gibbons has shrunk from about 30 meters to 2 meters thanks to the day-to-day companionship.

"One day, I was patrolling in the forest and a gibbon suddenly jumped to the ground and picked up some fruit that had fallen from a tree. It was just 2 meters in front of me, but it didn't run away. It just glanced at me and continued to eat the fruit. We stayed like that for about 10 minutes－I think it regarded me as another wild species," he said.

In 2013, Li witnessed a gibbon couple produce a youngster. "I named the father Xin and the mother Ping, and then gave the baby the name Xinping, the same pronunciation as the county's name," he said.

In recent years, Li has recorded important activities, including how the mother trained her offspring, who was very timid before the age of 2 and clung to her fur all day.

"Ping held the baby's legs, hung it upside down and swung it gently. We think this helped Xinping become used to the feeling of swinging from tree to tree in the forest," Li said.

Moreover, he also noticed that family members share emotional fluctuations, just like humans.

"Early in the day, we always hear the loud, unique morning calls between females and males. But one day, I noticed that Ping wouldn't echo Xin's calls because he had taken some fruit from her the day before. I was astonished that she was in a sulk with her husband, which is also common between human couples," Li said.