[ICCB 2019] Gibbon adults in Merapoh, Pahang, are at “fairly good” levels, reveals the latest survey of these small apes. The status of juvenile gibbons however, is still unknown.
That gap in gibbon data causes concern, especially with deforestation in the area, says Adilah Suhailin binti Kamaruzaman, graduate student researcher at Universiti Sains Malaysia and leader of the Merapoh gibbon survey. Adilah presented her findings on 25 July at the International Congress for Conservation Biology, Kuala Lumpur.
(Photo: A Lar gibbon, also called white-handed gibbon, is one of the three species of gibbons found in Peninsular Malaysia. Credit: Gibbon Protection Society Malaysia/Infinim Creative Productions)
Peninsular Malaysia is home to three gibbon species: siamang (Symphalangus syndactylus), Lar gibbon (Hylobates lar), and agile gibbon (Hylobates agilis). All three are considered endangered and declining due to logging and poaching.
Outdated assessment of gibbon numbers however, put conservation measures into question. The last comprehensive report of gibbon numbers in Peninsular Malaysia was published in 1974. Much of the peninsula’s forests has since been cut or sliced into fragments.
In her presentation, Adilah showed a map of forest reserves in Merapoh. The forest reserves are bisected by a highway and fringed by plantations and clearings.
As the forests shrink, nobody knew how the gibbons were faring there, she said pointing to the forests. Her work provides a timely assessment of gibbons in the area.
Can’t see them
But these shy animals live in the canopy and are very difficult to spot. “Gibbons can cross trees above us without us realising it,” Adilah tells Macaranga. “Very smooth, very agile, very gentle.”
On the other hand, it’s easy to hear gibbons. “Gibbons like to karaoke,” says Adilah, referring to the gibbons’ characteristic song-calls. Their calls can be heard for kilometers.
At first, Adilah used to mistake male gibbon calls—which are shorter than females—for those of a great argus pheasant. But she learned quickly. “When you get to know it’s a gibbon call, then you feel magical,” she says. “Like, ‘wow’!”
Over two months in 2018, Adilah surveyed gibbons in Sungai Yu and Tanum forest reserves, Merapoh. She divided her team into three groups that stood in a triangle, each positioned hundreds of meters away from another.
For five hours in the morning, each group listened for gibbon calls and recorded the direction from which they came.
Adilah then combined data from three groups to triangulate the locations of the calling gibbons. If the gibbons were located more than 2 km apart, she considered them different groups.
More groups now
She found that in Merapoh, there were 3.55 groups of Lar gibbon and 2.75 groups of siamang per squared-kilometer. Her method cannot determine how many individuals there are, but a gibbon group, or family, is unlikely to exceed 6 individuals.
Earlier studies had set densities below 2 groups per square-kilometer as a low gibbon level. Going by such standards, gibbons in Merapoh are doing fine, though logging remains a threat, says Adilah.
But strictly speaking, her results cannot be compared against earlier surveys because of different methods used.
What about juveniles?
Adilah is actually more concerned about juvenile gibbons. Gibbons learn to sing, and juveniles cannot master full songs. So far, Adilah has only heard incomplete gibbon songs “once or twice” in Merapoh.
She fears that only gibbon adults are faring well in the forest. Without juveniles, the gibbons in Merapoh might die out. “We want to know if the offspring are surviving,” she says.
Adilah’s work in Merapoh adds to on-going gibbon surveys in Ulu Muda, Taman Negara and Royal Belum, she says. Connecting all this research would provide a more complete picture of gibbon numbers in Peninsular Malaysia, which would inform their conservation.
This is a part of our reporting on the International Congress for Conservation Biology, July 21-25, 2019, Kuala Lumpur.