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Forest loss threatens territorial gibbons in southern Borneo

  • Bornean southern gibbons have the largest territories of any species in their genus, a new study has found.
  • These large home ranges, combined with the species’ intense territoriality, puts it at particular risk of habitat loss as a result of deforestation and fire.
  • The findings of this research demonstrate that this endangered species needs large areas of unbroken forest.

Gibbons living in southern Borneo have the largest territories of any of their close relatives, according to a new study. From a conservation perspective, those large ranges are a liability, putting them at higher risk when their habitat is wiped out by fire or deforestation.

The research, published July 31 in the journal PLOS ONE, draws on nearly nine years of data on four groups of Bornean southern gibbons (Hylobates albibarbis) living in the peatlands of the Indonesian province of Central Kalimantan. Combining the GPS locations of the groups with exhaustive observations of the apes’ behaviors, the team found that this species defends a “core range” of 21 to 52 hectares (52 to 128 acres) where they sleep and communicate with each other and other groups through hooting “duets” or “codas.”

A Borneo southern gibbon at a safari park in the Netherlands. The species is also known as the white-bearded gibbon. Image by Tim Strater via Wikimedia Commons (CC BY-SA 2.0).

They also ply more expansive “home ranges” of almost 150 hectares (371 acres) in search of food. Unlike the core areas, which rarely overlap with those of other groups, gibbons are more apt to share parts of their home ranges.

Still, gibbons tend to stick to the ranges they’ve secured in the forest for years at a time, Susan Cheyne, a biologist with the Borneo Nature Foundation and the paper’s lead author, said in a statement. That stalwart commitment to such large territories could be a recipe for conflict with other gibbon groups if they lose parts of their forest range and are forced into a rival group’s territory. During the study, one of the groups had to shift its range to the west when fires swept through parts of Borneo in 2015.

The concern is that forest loss as a result of fire, at the hands of loggers or to make way for agriculture could push this IUCN-listed endangered species into splinters of forest too small to support it.

A young gibbon in Central Kalimantan. Image by Wibowo Djatmiko via Wikimedia Commons (CC BY-SA 3.0).

“Gibbons need large areas to survive and linking forests,” the authors write, “and reducing fragmentation is the key to their conservation.”

Cheyne and her colleagues argue that insights into the behavior of gibbons can help conservationists and land managers come up with strategies to help these animals survive.

“Understanding how Gibbons use the forest is critical to their conservation,” Cheyne said in the statement. “These data can feed into creating protected areas of suitable size and habitat quality to maintain viable populations of the singing, swinging small apes.”

A white-bearded gibbon, pictured here in West Kalimantan, Indonesia. Image by Wibowo Djatmiko via Wikimedia Commons (CC BY-SA 3.0).

Banner image of a young male gibbon courtesy of the Borneo Nature Foundation. 

Citation:

Cheyne, S. M., Capilla, B. R., K., A., Supiansyah, Adul, Cahyaningrum, E., & Smith, D. E. (2019). Home range variation and site fidelity of Bornean southern gibbons [Hylobates albibarbis] from 2010-2018. PLOS ONE, 14(7), e0217784. doi:10.1371/journal.pone.0217784

Nijman, V., Richardson, M. & Geissmann, T. (2008). Hylobates albibarbis (errata version published in 2018). The IUCN Red List of Threatened Species 2008: e.T39879A128972094. doi:10.2305/IUCN.UK.2008.RLTS.T39879A10279127.en. Downloaded on 29 July 2019.

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