The population of Hainan gibbons, a first-class national protected species in China, has increased from less than ten in the 1980s to 37 this year thanks to the preservation efforts of local wildlife professionals.

Known as the world's rarest primate, Hainan gibbons have been listed as critically endangered by the International Union for Conservation of Nature.

The black-crested apes can only be found in the rainforests in south China's island province of Hainan. They live in rainforest trees over 10 meters high, rarely setting foot on the ground out of prudence.

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

Fortunately, the population of the species has recently seen a bounce-back for three years in a row as local professionals launched a plan to preserve their habitats and keep a close eye on their living status.

Every day, the forest rangers set off before first light and go look for the gibbons by tracing their voices, which can echo as far as kilometers in the mountains.

"We need to arrive at the monitoring spot at 05:00 and listen to the calls of the gibbons. Then we trace them and capture footage to learn about their living habits and the types of plants that they feed on," said Lin Qing, who has been working as a forest ranger for 13 years.

To better protect these rare animals, the local forestry department has invited experts from universities to help forest rangers observe and record the gibbons' activities and habits.

The latest mission lasted 15 days, during which researchers and rangers would orbit the habitats of the gibbons, count the number, record their ages, take photos, shoot videos and collect ape feces, providing first-hand materials for scientific research.

"We mainly keep track of the number of their troop and their distribution and habitat. We also monitor their physical health and keep data on their behavior," said Wang Xingliang, a research assistant from the School of Life Sciences of Guizhou Normal University.

To save Hainan gibbons from extinction, the province's forestry department has partnered with non-governmental organizations to restore more than 330 hectares of its habitat and plant more than 300,000 trees to provide food for the gibbons. They have also built several ecological corridors to expand the gibbons' habitat.

Zhou Zhaoli, vice captain of the Hainan gibbon monitoring team, said they also installed about 320 infrared cameras in the forest to better capture the life of the gibbons while reducing disturbances from mankind.

"The best means of protection is to minimize contact between humans and the gibbons, intervene as little as possible and let the habitat retain its natural state," said Zhou.

The current population of 37 gibbons is made up of six families, according to the Hainan Tropical Rainforest National Park.