Yunnan snub-nosed monkeys are popular among people because of their humanlike faces with bright red lips. [Photo provided to China Daily]

Over 1,000 dwell in Weixi's 330-square-kilometer park, according to its statistics, making it the country's largest reserve for the species.

Yu also looks out for fires and hunts for poachers.

The ranger hasn't seen poachers face-to-face in over a decade on the job - but he has found ammunition casings.

"Villagers have protected the monkeys since I was a child," says Yu, who's in his 50s.

"But we have to protect them from outsiders."

The park received about 20,000 visitors last year, administrator He Liqing says.

"We can't allow unfettered tourism," he says.