Simias concolorsimakobou(Also: pig-tailed langur)

Geographic Range

Simias concolor (the pig-tailed langur) is presently found only on the Mentawai Islands off the west coast of Sumatra in Indonesia. This species has been eliminated entirely from some islands due to logging and hunting by humans. (Burton, 1995; Eudey and Members of the Primate Specialist Group 2000, 2004)


The habitat of S. concolor includes hillsides in primary forests. It is uncertain whether S. concolor also resides in swamps and mangrove forests with different sources stating different information regarding its presence in these environments. This species is entirely arboreal and only comes down from the trees when it is disturbed. (Burton, 1995; Nowak, 1999)

Physical Description

The body length of S. concolor ranges from 490 to 550 mm in males and from 460 to 550 mm in females. The average weight is around 8.7 kg for males and 7.1 kg for females. The tail length of S. concolor varies between 14 and 15 cm. Two color varieties exist for S. concolor, a dark grey phase and a creamy buff phase, with the dark grey phase being more common. The creamy buff phase is found in roughly one in four individuals. The limbs are of equal length and the tail is rather short compared to other primate species in the subfamily Colobinae. Adult pig-tailed langurs have black faces and small snub-noses. The coat of the dark phase of S. concolor is blackish-brown with light speckled hair on the nape, shoulder, and upper back. The tail of this species is not only short, but also hairless, except for a small amount of hair at the tail tip. (Ankel-Simons, 2000; Burton, 1995; Noë and Bshary, 2001)

  • Sexual Dimorphism
  • sexes alike
  • Range mass
    7.1 to 8.7 kg
    15.64 to 19.16 lb
  • Range length
    460 to 550 mm
    18.11 to 21.65 in


Males have been observed participating in displays of strength that consist of leaping through the trees to attract mates. The social group of S. concolor includes one male and up to four females with which the male mates. (Vogel and Winkler, 1990; Woltanski, 2004)

Few data exist regarding the reproductive cycle of S. concolor, but it is believed that a single birth occurs sometime during June and July. This species also exhibits sexual swelling, a trait that is rare in other Asian colobines. (Burton, 1995)

  • Average number of offspring

Little is known about the parental investment of S. concolor, but there is information about their close relatives, proboscis monkeys, Nasalis larvatus. Female N. larvatus carry, nurse, and stay close to their young for about a year. While the males do not provide as much care as the females, they do protect their young from males from other groups. (Woltanski, 2004)

  • Parental Investment
  • altricial
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female


No information is available regarding the lifespan and longevity of S. concolor, but its relative N. larvatus lives at least 23 years in captivity. (Woltanski, 2004)


Little is known about the behavior of S. concolor because there are so few in such a limited geographical range as well as the difficulty in spotting them in their dense forest habitat. There are two distinct group types exhibited in S. concolor, family groups and groups of all males; each exhibit unique behaviors. The most common type of grouping is the family group of one male and up to 4 females. These groups can be formed with a single adult couple and their young or with more than one adult female with a single male. Family group members maintain very close proximity, rarely traveling more than 5 m (16 ft.) away from one another. They also restrict vocal communication, only using it at designating group boundaries and as a warning to predators. The all male groups exhibit behaviors that produce excessive noise as they travel through the forest, communicate with others, and leap in displays of strength. (Ankel-Simons, 2000; Nowak, 1999; Tilson, 1977; Vogel and Winkler, 1990)

  • Range territory size
    6600 to 202000 m^2

Home Range

The size of the average S. concolor territory is between 16.3 and 50 acres (6.5 to 20 ha). Individuals are not observed deep inside other territories, but are seen on the margin of adjacent territories. During encounters with other groups, the males approach, make loud vocalizations and return to their home territory with the other group members following behind. Chasing and fighting are generally not observed during these encounters. (Tilson, 1977; Vogel and Winkler, 1990)

Communication and Perception

Communication between individuals and groups of S. concolor is achieved by producing loud calls in a series of vocalizations ranging from 2 to 25 nasal barks. These barks can travel at least 500 m through the rainforest. The purpose of these calls is believed to be to maintain group structure and boundaries. Males call out with loud nasal barks and females reply with sharp squeals. It is also likely that chemical cues are used widely in communicating reproductive state and that vision and touch are important. (Burton, 1995; Tilson, 1977)

Food Habits

This species eats leaves, fruits, and berries. Feeding occurs after sunrise near the trees used for sleeping and again in the afternoon. Adult males lead the foraging and the females and young follow behind . (Burton, 1995; Tilson, 1977)

  • Plant Foods
  • leaves
  • fruit
  • flowers


The only known enemy or predator of S. concolor is man. Other large predators on the Mentawai Islands include crested serpent eagles (Spilornis cheela) and pythons (Python reticulatus), both may also prey on S. concolor. (Vogel and Winkler, 1990; Whitten and Whitten, 1982)

Ecosystem Roles

There is little available information on the ecosystem role of the pig-tailed langur. They may aid in seed dispersal of tropical fruiting trees.

Economic Importance for Humans: Positive

Pig-tailed langur meat is considered a delicacy. These are important members of the ecosystems in which they live, they could contribute to the development of the ecotourism industry in the Mentawai islands. (Burton, 1995)

Economic Importance for Humans: Negative

There are no known adverse affects of S. concolor on humans.

Conservation Status

Pig-tailed langurs are listed as an endangered species under the IUCN. The population consists of fewer than 10,000 individuals. Habitat loss due to logging is the main cause of population decline. Hunting is also a major problem, especially in the Pagai Islands because S. concolor meat is considered a delicacy. This species receives protection at the Teiteibatti Wildlife Reserve, located on the only island that provides such security. It is believed that the population size of S. concolor has decreased by 50% during the last decade and will most likely continue to drop another 50% during the next decade. (Burton, 1995; Eudey and Members of the Primate Specialist Group 2000, 2004; Nowak, 1999)

Other Comments

This species was previously recognized under the name Nasalis concolor.


Tanya Dewey (editor), Animal Diversity Web.

Lyndsay Rankin (author), Michigan State University, Barbara Lundrigan (editor, instructor), Michigan State University.



uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.


Referring to an animal that lives in trees; tree-climbing.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


uses smells or other chemicals to communicate

  1. active during the day, 2. lasting for one day.

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.


an animal that mainly eats leaves.


A substance that provides both nutrients and energy to a living thing.


an animal that mainly eats fruit


An animal that eats mainly plants or parts of plants.

island endemic

animals that live only on an island or set of islands.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).


having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.


found in the oriental region of the world. In other words, India and southeast Asia.

World Map


having more than one female as a mate at one time


rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season


remains in the same area


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


Living on the ground.


defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement


the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.


uses sight to communicate


reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.


Ankel-Simons, F. 2000. Primate Anatomy: An Intrduction. San Diego, California: Academic Press.

Burton, F. 1995. The Multimedia Guide to the Non-human Primates. Scarborough, Ontario: Prentice Hall Canada.

Eudey, A., Members of the Primate Specialist Group 2000. 2004. "IUCN Red List of Threatened Species: Simias concolor" (On-line). Accessed March 16, 2006 at

Nowak, R. 1999. Pig-tailed Langur. Pp. 596-597 in Walker's Mammals of the World, Vol. 1, 6th Edition. Baltimore: The Johns Hopkins University Press.

Noë, R., R. Bshary. 2001. Colobus and Leaf Monkeys. Pp. 380-395 in D Macdonald, ed. The Encyclopedia of Mammals, Vol. 2, Revised Edition. New York: Facts on File.

Tilson, R. 1977. Social organization of simakobu monkeys (Nasalis concolor) in Siberut Island, Indonesia. Journal of Mammalogy, 58(2): 202-212.

Vogel, C., P. Winkler. 1990. Langurs and Colobi. Pp. 296-324 in S Parker, ed. Grzimek's Encyclopedia of Mammals, Vol. 2, 1 Edition. New York: McGraw-Hill Publishing Company.

Whitten, A., J. Whitten. 1982. Preliminary observations of the Mentawai macaque on Siberut Island, Indonesia. International Journal of Primatology, 3(4): 445-459.

Woltanski, A. 2004. "Nasalis larvatus" (On-line). Animal Diversity Web. Accessed April 18, 2006 at