Evolving conservation

Over the past two decades, monitoring methods have advanced in distinct waves, experts said.

Around 2008 and 2009, teams began using vocalization triangulation. By fanning out across the forest and timing the gibbons' morning calls from multiple positions, they could map family groups with increasing accuracy.

The early 2010s brought the "three-designated" system: designated people monitoring designated apes in designated groups, year after year. "When you first start monitoring them, they are very afraid of people," said Ding Jiatuan, current chief of the Nankang Management Station and Yang's supervisor. "You have to habituate them, get them used to you. You can't keep changing the monitors."

The latest innovation, introduced just two or three years ago, is acoustic monitoring. Small recording devices capture individual vocal fingerprints. "Each gibbon has a unique voice," Li Jiahua explained. This allows researchers to identify solitary individuals who rarely reveal themselves.

The recordings may eventually serve a new purpose: matchmaking. A documentary project, A Song For Love: An Ape with An App, used real-time audio to connect a captive male at a Beijing zoo with a solitary female in the Gaoligong Mountains. "They responded strongly to each other," Li said — planting the idea that recordings could one day help introduce isolated individuals across the fragmented forest.