Northern buffed-cheeked gibbon – Nomascus annamensis – Thinh, Mootnick, Thanh, Nadler & Roos, 2010

Science name: Nomascus annamensis – Thinh, Mootnick, Thanh, Nadler & Roos, 2010

Taxonomic:  Animalia>> Chordata>> Mammalia>> Primates >> Hylobatidae >> annamensis

Species status: Endemic ; IUCN status: EN (Endangered Species)

Description: Physical Characteristics:
Males have black fur with some silver highlights, and brown fur on the chest. Their cheeks are yellowish-orange, giving them the “yellow-cheeked” name. Females are lighter, with golden-beige to orange fur and black patches on the chest and head. The face in both sexes is bare with a dark, almost black skin tone.

Distribution and habitat:

Altitude:
Nomascus annamensis inhabits elevations between 100 to 1,200 meters above sea level.

Range:
This species is found in southern Laos, northeastern Cambodia, and central and southern Vietnam, east of the Mekong River. Notable populations occur in Virachey National Park (Cambodia), Dak Rong and Phong Dien Nature Reserves (Vietnam), and Xe Pian National Protected Area (Laos). Lao PDR likely holds the largest global population.

Habitat:
Nomascus annamensis primarily inhabits broadleaf evergreen and semi-evergreen forests. These gibbons are arboreal and diurnal, living in family groups within a home range of about 50 hectares. The species is also known to feed in and navigate through dense forest canopies. Logging and forest degradation threaten their habitat, contributing to a continuing decline in forest quality.

Behaviour and ecology:

Social Structure:
Nomascus annamensis lives in monogamous family groups consisting of a male, female, and their offspring. Territorial duets between males and females are used for communication, and the calls, which are species-specific, are most often heard in the early morning hours. Groups may have a home range of 50 hectares, and movement patterns are closely linked to forest canopy structure.

Feeding Habits:
This species is primarily frugivorous, consuming a diet of fruits, supplemented by leaves, young shoots, and flowers. Occasionally, they have been observed feeding on small animals such as squirrels or lizards. Food sharing within the group has also been observed.

Reproduction:
Gibbons generally live in monogamous pairs, and each pair defends a territory. Reproduction occurs year-round, and the gestation period lasts about seven months. A single offspring is born, which remains with the family group for several years before dispersing. The generation length is about 15 years.

Conservation and status:

IUCN Red List Category and Criteria:
Nomascus annamensis is listed as Endangered under criteria A4cd. The species faces severe threats from habitat loss and hunting, which continue to drive population declines.

Population Trend:
The population is decreasing due to habitat degradation, illegal logging, and hunting pressure, particularly in Vietnam and Laos. Estimates suggest key populations of over 220 groups in Vietnam, 500 groups in Cambodia, and potentially significant populations in Laos, though population data remain limited.

Threats:
The main threats to Nomascus annamensis are habitat destruction from illegal logging and forest conversion, hunting for the pet trade, and traditional medicine. In Cambodia and Vietnam, forest loss due to agricultural expansion and land concessions is significant, further threatening their habitat. Although hunting pressure is lower in Cambodia, it remains a serious threat in Laos and Vietnam.

Conservation Actions:
Nomascus annamensis is protected under various conservation measures, including protected area management and anti-poaching efforts. Acoustic monitoring surveys in areas like Virachey National Park and Veun Sai-Siem Pang National Park in Cambodia help track population trends. The species is also listed in Appendix I of CITES, prohibiting international trade. However, ongoing habitat loss and illegal logging continue to pose significant challenges to its conservation.