Shrinking forest a threat to Sumatra's gibbons

Shrinking forest a threat to Sumatra's gibbons

Syofiardi Bachyul Jb, The Jakarta Post/Padang

A researcher has warned that the gibbon population of Kerinci
Seblat National Park are on the brink of extinction due to
illegal logging and land clearance.

Gibbons are arboreal apes indigenous to Southeast Asia and are
highly endangered, with only 13 species known to exist in the
wild. They are characterized by their acrobatic swinging through
treetops, suspended by their hands, and are known for their
territorial vocalization, or song, which are emitted from a
throat sac that can inflate to the size of their heads.

The government must take affirmative action to prevent the
protected animals from becoming extinct, said Achmad Yanuar, a
doctorate student from the Wildlife Research Group of the
University of Cambridge's anatomy department.

Yanuar has just completed a two-year research project on the
destruction of the socio-ecological habitats of the large black
gibbon of Sumatra, also known as the Sumatran siamang
(Symphalangus syndactylus), and the lowland agile gibbon
(Hylobates agilis unko) as part of his Ph.D. program.

During his research, Yanuar discovered that the virgin forest
in the park presently covers about 1.4 million hectares (ha).

An estimated 90,000 Sumatran siamang and 150,000 lowland agile
gibbon are thought to live within this territory, which were
calculated by multiplying population density per square kilometer
with the area of the national park.

The Sumatran siamang prefer living in highland altitudes of
800 meters to 1,200 m above sea level. Mountainous forests,
typically classified as 1,500 m to 2,300 m above sea level, are
more densely populated by the Sumatran siamang, as lowland agile
gibbon are seldom found at such heights.

The lowland agile gibbon, on the other hand, live in areas of
about 500 m to 800 m above sea level.

"In the lowland forests on the western part of the park, the
population density of the Sumatran siamang is higher than the
lowland agile gibbon, whereas on the eastern part, there are more
lowland agile gibbon compared to the Sumatran siamang," Yanuar
said.

At least 40 percent of the total park area has an altitude of
less than 1,000 meters above sea level, and comprise the forest
habitat of the Sumatran siamang and lowland agile gibbon.

"Of the 500 ha forested area on the edge of the park where I
conducted my research, 60 percent has vanished due to illegal
logging and land clearance. Only about 30 percent of the primary
forest remains," Yanuar said.

The shrinking forest contributes to the plight of the lowland
agile gibbon and Sumatran siamang populations, whose survival
depends on their habitat. As gibbons live in treetops, the
destruction of forest areas means they will be forced to travel
on the ground, making them easy prey to predators and poachers.

"They probably roam along the ground as they are not able to
live in the trees, and that's the moment when they are caught by
people to be kept as pets or sold," Yanuar said.

In addition, gibbons are one of the few monogamous primate
species and live in nuclear families consisting of a mated couple
and their young offspring, marking their territory by a song
unique to each family group. As the forest continues to be
destroyed, families will be confined to smaller and smaller
territories, while new couples will find it difficult to
establish their own home territories, as any available tree tops
would be occupied by other gibbon families.

Yanuar's research, funded by the Gibbon Foundation, shows that
more than 40 locations within the national park -- including
Bangko in Jambi province and South Solok in West Sumatra -- are
facing serious problems with illegal logging and land clearance,
particularly for oil palm plantations, which had become an
industry trend.

To save the gibbons, their habitats must be conserved, he
said, particularly as lowland forests of up to 800 m above sea
level were most susceptible to destructive human activity -- the
very areas that make up the gibbons' natural habitat.

"Therefore, such forests must be protected, especially those
within the park," he said, underlining that the government needed
to draw up an action plan to combat illegal logging and land
clearance.