Mountain ranger records hoolock gibbons' life track(2)

However he tried, he never got a clear photo, face to face, as the creatures are very vigilant. Any suspicious sound scares them away before a camera can focus.

In 2005, Li was transferred from Longyang to Nankang Station, a better place, he believed, to observe them. Before moving to Nankang, he was trained in wildlife photography and equipped with a high-end digital camera and a 300-mm lens.

One day in May, Li took a sleeping bag and the camera to a possible hoolock habitat. The next morning, he was woken up by howls.

"It just happened. Two hoolocks, a black male and a gray female, dangled from the tree above my head. I can still see their gray faces and white brows." Li held his breath and snapped away.

The noise of the camera shutter betrayed him, but to his surprise, they didn't flee. The hoolocks and Li stared at each other silently for a while, until one of them made a long howl and disappeared into the treetops.

"They must have known me. We were familiar to each other," he recalls with emotion.

Li captured China's first clear photos of the eastern hoolock gibbon. His decade-long study has provided an unparalleled contribution to the knowledge and protection of this species.

He has also taken more than 500 photos of other protected primates in China, such as the Phayre's leaf monkey, the Assam macaque and the slow loris, establishing Nankang Station as a prime site for primate observation.