A primate on the brink - Cao vit gibbon even closer to extinction than feared

Revised head count

The gibbon count was also assisted by drones mounted with thermal imaging cameras, which enabled the team to pinpoint particular groups more easily and count the number of individuals in them more accurately.

The cao vit gibbon is one of the world’s rarest primates, thought to be extinct until it was rediscovered by Fauna & Flora in 2002. Accurate monitoring of the last remaining population is critical to the species’ survival, but traditional ground-based monitoring methods, such as using binoculars and cameras, are tricky in this steep, almost inaccessible, terrain and can be unreliable as the gibbons move rapidly through dense forest canopy.

What do these results mean?

The good news is that, despite the revised estimate, there is no evidence that the cao vit gibbon population has declined. Thanks to the vital work of Fauna & Flora and our partners since this elusive ape’s rediscovery, gibbon numbers are still thought to be increasing, with the number of individuals in long-term monitored groups on the rise, and new groups having formed in recent years. The difference is due to accidental double-counting in previous surveys that used traditional species monitoring techniques.

The new and more accurate population estimate serves as a more robust basis for informing conservation management actions and tracking success over time. However, the cao vit gibbon is evidently in much more immediate danger from the threats posed by small population size than previously thought. These include loss of genetic diversity, inbreeding and vulnerability to unforeseen catastrophes. Conservation action, particularly habitat restoration to broaden the cao vit gibbon’s extremely limited range, is now more urgently needed than ever.

Project lead, Oliver Wearn, comments: “Cao vit gibbons are loud and lively singers. They defend their territories mainly by singing, and their calls can be heard from a kilometre or more away. Our community monitoring teams told us that each male adult gibbon has its own unique voice, just like we do, and so for this project we decided to take advantage of that. Thanks to this idea of ‘vocal fingerprinting’, we have been able to create a much more accurate picture of the size of the population, and where the territories of each group are. This new method is not only more accurate, but is non-invasive, enabling us to study the gibbons without disturbing their natural behaviour.”