It was in 1997 when Li Jiahong, a 63-year-old wildlife protection expert, first heard the shrill calls of the Skywalker hoolock gibbon, one of the world's most endangered primates.
Bursting from the canopies of the dense forest in the Gaoligong Mountains in southwestern China's Yunnan Province, the high-pitched, rhythmic sound "was like rolling down the hill, remote but very clear," says Li, who then worked at the Longyang preservation office of the Gaoligong Mountain National Nature Reserve.
