Identifying Characteristics:
- Overall coloration is a yellowish-brown.
- Adults have a red face.
- Hair on the crown of the head is very short.
- The back of the body is lighter brown than the front (Fa, 1985).
- The tail is of a medium length, shorter than 3/4 the length of the head and body, and covered with good hair.
- The outer buttocks and thighs are reddish-brown.
- The skin around the ischial callosities (buttocks) is round and hairless.
Biology and Ecology:
- Yellow monkeys live in environments with a wide range of temperatures, rainfall, and altitudes.
- From very cold to nearly 50°C.
- From very dry areas near deserts to areas with 10,000 mm of annual rainfall.
- From sea level to 3050m (Richie et. al, 1978).
- Social Behavior:
- Southwick et.al (1961a; 1964) reported that the monkeys live in groups of up to 50 individuals.
- Fooden (1971) observed 20 individuals in a group in Thailand in 1967.
- Reproduction:
- Sexual maturity: 42 – 48 months (Melnik, 1987).
- Gestation period: 164 days.
- Interbirth interval: 12 – 24 months (Ross, 1992).
- Lifespan: 29 years (Ross, 1991).
- Breeding season: Approximately 3 – 6 months (Melnik, 1987).
- Diet:
- Primarily fruits, seeds, leaves, buds, grasses, and other plant parts, as well as some invertebrates (Rochard, 1989).
- Almost 100 plant species are used as food (Lindburg, 1977).
- Activity:
- Diurnal, primarily terrestrial but also arboreal (Seth, 1986).
- Social structure: Multi-male, multi-female groups. Females often group together during the night.
- The dominant male leads the group but often remains on the periphery (Parker, 1990).
- Group size: Typically 10 – 50 individuals, sometimes up to 90 (Seth, 1986).
- Habitat:
- They prefer primary and secondary forests, dry forests, mixed forests, bamboo forests, flooded forests, tropical sparse forests, pine forests, bush, tropical humid forests, and areas near agricultural land.
- They live up to an altitude of 3000m (Parker, 1990).
- Water is a limiting factor for their distribution.
Distribution:
- Within Vietnam: Distributed from the northern border to the Central Highlands provinces.
- Worldwide: South and Southeast Asia.
Value:
- Used in the production of vaccines against polio, and as a model for scientific research.
- Currently, the National Institute of Hygiene and Epidemiology (Ministry of Health) has organized breeding on Rều Island (Quảng Ninh) with thousands of animals to produce vaccines.
- Needs to be protected in nature to preserve the valuable gene pool.
Conservation Status:
- Before 1975, this species was still very common in the forests of the northern provinces to the Central Highlands, over an estimated area of >20,000km2.
- Since 1975, the species’ situation has changed dramatically. The population has declined sharply.
- There are currently about 50 subpopulations.
- Reasons for change: Habitat encroachment, deforestation, reduction of natural forest area, and hunting for meat, traditional medicine (cao), trade and export.
IUCN Red List Status:
- LR nt (Lower Risk, near threatened)
Conservation Measures:
- Included in the Vietnam Red Book 2000 and the list of species in need of protection by the Forestry sector (Appendix IIB Decree 32/2006/ND-CP dated April 22, 2002 of the Government).
- Effective implementation of laws, regulations, and decrees of the government on the protection of wildlife.
- Establishment of nature reserves and management programs for wildlife in general and threatened species in particular.