HAIKOU - Researchers have found a Hainan gibbon cub, which means the gibbon population has recovered to 33 in five families in South China's island province of Hainan, sources with the provincial forestry authority said Tuesday.

Hainan gibbons, known as the world's rarest primates, are identified as critically endangered by the International Union for Conservation of Nature.

Inspectors from the Hainan tropical rainforest national park administration spotted a female gibbon cuddling a cub in Dongbengling, Baisha Li autonomous county, on Aug 29 and took pictures, which experts later confirmed that the gibbons had formed a new family.

Zhou Yadong, chief engineer of the forestry department of Hainan, said the discovery proved the original and the new habitats of gibbons were connected, and the area of their habitats have been expanding.

Zhou said it also proves the tropical rainforest is expanding, which contributed to the protection of Hainan gibbons.

Numbering over 2,000 in the 1950s, the Hainan gibbons' population plunged to about seven in the 1980s, with excessive hunting and lumbering pushing them to the brink of extinction.

Typically living in rainforest trees over 10 meters tall, the Hainan gibbons, with long arms and legs but no tail, rarely set foot on the ground, making captive breeding difficult.