A group of experts went into forest in Jingdong Yi Autonomous County of southwest China's Yunnan Province for a survey on the population of eastern black crested gibbons.

On Thursday morning, the experts set out on foot to the mountain area of Wenpu Village in Jingdong, to closely observe eastern black crested gibbons and record their yelling.

Eastern black crested gibbons live in family on trees. Usually, a gibbon family is led by a male who has one spouse or two. The small apes would like to yell after getting up in the morning and the yelling varies from family to family. So it is important for the survey to record the yelling of gibbons, according to Fan Pengfei, professor with the School of Life Sciences of Sun Yat-Sen University from Guangzhou.

"If we could record the yelling on recorders or mobile phones, we could judge how many groups of eastern black crested gibbons we have in this area, how many adult males and females there are in each group, and whether they carry babies. We can make judgment on such information from their yelling," said Fan.

Data of the survey conducted ten years ago show that there were 87 groups of some 500 eastern black crested gibbons permanently living in the Wuliang Mountain area in Jingdong. In recent years, the county has continuously promoted the protection of the gibbons and hired local villagers to patrol the area and enforce relevant laws. With years of hard work, the population of gibbons is continuously growing.

The survey involves five groups of more than 30 experts, who are mainly to collect sounds and visit communities to obtain more sufficient data of local eastern black crested gibbons.