White-Bearded Gibbon

Explanation: Here we were, on a riverboat trip up the Sekonyer River in Tanjung Puting National Park in the Indonesia portion of southern Borneo. We put in at the dock at the Leaky Orangutan Feeding Station, and walked the elevated plank trail to watch the daily feeding of orangutans ... when suddenly a dark form swept in overhead among the subcanopy branches, an interloper.

Keeping its distance from both the tourists and the orangutans was this large male Bornean white-bearded gibbon, staying apart but remaining watchful of the scene below.

Listed as an Endangered species in the IUCN Red List, as are some other gibbon species, Bornean white-bearded gibbons are found only in the Kalimantan region of southern Borneo. Populations are declining, with main threats being logging and conversion of their native tropical forests to agriculture and wood and pulp plantations. They are also subject to illegal hunting and capture for the pet trade. At present, there are no recovery plans in play and no population monitoring activities, although the species in included in international trade controls.

Bornean white-bearded gibbons are largely frugivorous, feeding on arboreal figs and fruits, with occasional taking of leaves and insects. As such, they can play a key ecological role in the forest as seed-dispersers.

These gibbons are quite territorial, defending their home range of about 125 acres (50 ha) in small groups of male, female, and offspring. They issue loud calls in the morning with howling duets to signal their territory, and do not seem to interact regularly with adjacent family groups.

Information:
Yanuar, A., D. Chivers, I. Hilman, C. Saleh, I.D.W. Putra, S. Purnomo, and K. Wasman. 2020. Population Survey of Bornean White-Bearded Gibbon, Hylobates albibarbis,in Two Selective Logging Concessions in Central Kalimantan and West Kalimantan. International Journal of Primatology 91(2):108-121.

EPOW - Ecology Picture of the Week