Nomascus leucogenys is better known as the white-cheeked gibbon. This species is found only in Southeast Asia. They primarily populate Laos, Vietnam, and Southern China. In Vietnam, N. leucogenys is found to the southwest of the Song Ma and Song Bo Rivers. A close relative, Nomascus concolor, is found northeast of the Song Ma River and northeast of the Song Bo River. The geographical separation is crucial to distinguishing these two gibbon species because N. leucogenys and N. concolor are extremely similar in appearance. ("Smithsonian National Zoological Park", 2006; Cawthon Lang, 2006; Geissmann, et al., 2000; Muller, et al., 2003; Takacs, et al., 2005; Wilson and Burnie, 2005)
Nomascus leucogenys live in the canopy of subtropical rainforests. White-cheeked gibbons hardly ever descend to the forest floor. ("Smithsonian National Zoological Park", 2006; Cawthon Lang, 2006; Geissmann, et al., 2000; Wolfheim, 1983)
Nomascus leucogenys are not sexually dimorphic in size. Both males and females grow to weigh an average of 5.7 kg. Likewise, both sexes reach similar lengths, from 45 to 63 cm long. White-cheeked gibbons are, however, dimorphic in fur color. All infants are born with cream-colored fur. At two years of age, the infants' fur changes from cream to black, and they develop white patches on their cheeks. At sexual maturity, males stay black with white cheeks. Females turn back to the original cream color and they lose the majority of their white cheek color. Like all species of gibbons, white-cheeked gibbons do not have tails. They have exceptionally long forelimbs and hindlimbs. Their bodies are built for an arboreal lifestyle. They have an opposable hallux and an opposable pollex. This makes grasping food and holding branches easy. Furthermore, their hands are hook shaped, facilitating brachiation. The body of N. leucogenys is small and they have a remarkably upright posture. Their molar teeth are bunodont and their canines are large and showy. The dental formula is 2/2, 1/1, 2/2, 3/3. Nomascus leucogenys was considered a subspecies of crested gibbon, N. concolor, until 1989. The main difference between the two species is the “mohawk” tuft at the top of the head of N. leucogenys. ("Smithsonian National Zoological Park", 2006; Cawthon Lang, 2006; Geissmann, et al., 2000; Vaughan, et al., 2000; Wilson and Burnie, 2005)
White-cheeked gibbons become sexually mature at about six to seven years of age. At this point, Nomascus leucogenys females have a menstrual cycle that lasts about twenty-eight days. They breed throughout the year. Once fertilization occurs, a female has a gestation period of seven months. When the infant is born, it holds on to the mother for nearly two years. After the two-year period, the infant is weaned. ("Smithsonian National Zoological Park", 2006; Geissmann, et al., 2000; Miles and Caldecott, 2005)
Parental care in white-cheeked gibbons is not restricted to females. Unlike many mammals where the female is the primary care giver, N. leucogenys share the responsibilities between males and females. An infant reaches physical maturity at three years of age and becomes independent at around six to seven years of age. During the period of parental care, the infant learns to groom, differentiate between food sources, and learns basic social interactions such as playing and social dominance. ("Smithsonian National Zoological Park", 2006; Geissmann, et al., 2000; Miles and Caldecott, 2005)
Nomascus leucogenys individuals are arboreal and live mainly in the canopy of forests. They travel through the trees by brachiation. While in the trees, white-cheeked gibbons spend a great deal of time eating. White-cheeked gibbons live in small families comprising a male adult and a female adult that mate monogamously. They usually have three to four offspring within the group. There is a hierarchy among the family. The female is dominant followed by her female offspring, male offspring, and the adult male is last. Nomascus leucogenys individuals spend much of their free time playing and grooming. White-cheeked gibbons also use vocalizations throughout the day to signal territory, and they are used in mating rituals. ("Smithsonian National Zoological Park", 2006; Cawthon Lang, 2006; Geissmann, et al., 2000; Miles and Caldecott, 2005; Vaughan, et al., 2000)
Nomascus leucogenys individuals signal territory by using vocalizations. They also use vocalizations in mating behaviors. In order to signal aggression, N. leucogenys resort to the common threat of opening their mouth wide to show their teeth. White-cheeked gibbons spend much of their time grooming and playing. Grooming and playing allow individual gibbons to form bonds. It is also likely that chemical cues, such as pheromones, are used to communicate reproductive state. (Geissmann, et al., 2000; Miles and Caldecott, 2005; Vaughan, et al., 2000)
Nomascus leucogenys are primarily frugivorous. They especially enjoy eating the pulp of fruits. They are important seed dispersers for some plants. In general, N. leucogenys eat and forage with their family. Unlike other primates that spend half of the day foraging and the other half of the day slumbering, white-cheeked gibbons search for food throughout the day. Early in the morning, they forage high in the canopy. When the sun begins to heat the canopy, they retreat to lower trees in the understory. They are frugivores, but along with fruit, white-cheeked gibbons also eat leaves, flowers, and insects. The type of food that they eat depends on precipitation. When there is a great deal of precipitation, fruit is plentiful and they do not have to travel far to find food. Conversely, they travel great distances in search of food when there is little rainfall. ("Smithsonian National Zoological Park", 2006; Geissmann, et al., 2000; Miles and Caldecott, 2005)
The main threat to Nomascus leucogenys is forest clearing, and therefore, their main predator is humans. It has also been documented that in North Vietnam, some people have hunted N. leucogenys for their meat. Nothing is known about other specific predators of Nomascus leucogenys, but eagles of the family Accipitridae, owls of the family Strigidae, and Panthera pardus are known to prey on N. concolor. Nomascus leucogenys, like N. concolor, live in the canopy and that makes them easy prey for large birds and arboreal carnivores. Gibbons are very agile and remain vigilant in their high, inaccessible habitats, all of which help them avoid predation. (Cawthon Lang, 2006; Crane, 2000; Miles and Caldecott, 2005; Wolfheim, 1983)
Miles and Caldecott (2005) reported that Nomascus concolor are kept as pets in Vietnam when infants are plucked from their mothers. As the infant enters adulthood they become a problem and are often abandoned by their owners. They are also kept at zoos around the world. It is unclear whether these authors studied Nomascus concolor or Nomascus leucogenys. (Miles and Caldecott, 2005; Wolfheim, 1983)
Nothing is known about the conservation status of Nomascus leucogenys, but members of the related species Nomascus concolor are endangered due to deforestation, logging, hunting and military activities. (Crane, 2000; Geissmann, et al., 2000; Miles and Caldecott, 2005)
A great deal of molecular research has been done recently on Hylobates phylogeny and greater ape phylogeny. There are four discrete divisions of lesser apes and these four subgenera include Bunopithecus, Hylobates, Symphalangus, and Nomascus. These are monophyletic groups. Before there was thorough DNA evidence, all white crested gibbons were considered members of a single species Hylobates concolor. Chromosomal evidence that is available today allows scientists to distinguish the white cheeked gibbon as a member of the subgenus Nomascus, which are characterized by having a diploid number of 52 chromosomes. Nomascus is found from southern China to southern Vietnam, and is found on Hainan Island. Fur coloration, anatomical data, and vocal data are also used to identify different species of gibbons. Within the subgenus Nomascus, there are four separate species that include N. concolor, N. gabriellae, N. sp. cf. nasutus, and N. leucogenys. White-cheeked gibbons have therefore been re-named Nomascus leucogenys. There are also subspecies within each species. For example, recent DNA evidence has distinguished Nomascus leucogenys leucogenys as the northern white-cheeked gibbon and Nomascus leucogenys siki as the southern white-cheeked gibbon. Due to the recent taxonomic advancements using DNA, it is not clear what species is being discussed in much of the older literature. (Geissmann, et al., 2000; Geissmann, 2002; Muller, et al., 2003; Roos, 2001; Takacs, et al., 2005)
Tanya Dewey (editor), Animal Diversity Web.
Tommy Boyd (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.
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.
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
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
to jointly display, usually with sounds in a highly coordinated fashion, at the same time as one other individual of the same species, often a mate
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.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
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 one mate at a time.
having the capacity to move from one place to another.
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.
the business of buying and selling animals for people to keep in their homes as pets.
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.
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.
breeding takes place throughout the year
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