Müller's Bornean gibbon

Müller's Bornean gibbon (Hylobates muelleri), also known as the grey gibbon, is a primate in the gibbon family, Hylobatidae.

Unlike other gibbon species, Müller's Bornean gibbon does not show sexual dimorphism in its fur coloration. Its fur is grey- or brown-colored with a ring of bright fur around its face. On the head, it often has a darkly colored cap. Weighing between 4–8 kg, it ranks among the smaller of the gibbons.

Müller's Bornean gibbon is endemic to the island of Borneo, inhabiting the northern and eastern part of the island. In the southwest of the island lives the Bornean white-bearded gibbon; their territories hardly overlap. Grey gibbons are diurnal rain forest dwellers, characterized by the long arms that all gibbons have, with which they brachiate through the trees. They live together in monogamous pairs, and defend their family territory against intruders with long, loud singing. Their diet consists primarily of fruits. Little is known about the reproductive patterns of this species, but it is thought to be similar to that of other gibbon species.

Müller's Bornean gibbon occurs in a number of protected areas, including Betung Kerihun National Park, Bukit Baka Bukit Raya National Park, Kayan Mentarang National Park, Kutai National Park, Sungai Wain Protection Forest and Tanjung Puting National Park in Indonesia and Pulong Tau National Park the Lanjak Entimau Wildlife Sanctuary and Semengok Forest Reserve in Malaysia.