Species Fact Profile: Northern White-Cheeked Gibbon (Nomascus leucogenys)

 Northern White-Cheeked Gibbon

                                                        Nomascus leucogenys (Ogilby, 1840)

Range: Southeast Asia (Laos, Vietnam) – believed to have been extirpated from southern China (Yunnan)

Habitat: Primary Evergreen Subtropical Rainforest, up to 1600 meters elevation (historically occurred at lower elevations, may be shifting habitat usage due to habitat loss)

Diet: Fruits, Leaves, Flowers, Eggs, Small Animals

Social Grouping: Breeding pair with offspring

Reproduction: Monogamous, generally for life.  Can breed year round.   Single infant born after seven month gestation period.  Infant clings to the mother for the first two years (having the same color fur as the mother at this point allows it to blend in with her fur), being weaned at the end of this period.  Both parents care for the infant.  Sexually mature at 6-7 years old.  Independent at 3-8 years old.  Have offspring every 2-3 years

Lifespan: 50 Years

      Conservation Status: IUCN Critically Endangered, CITES Appendix I

• Both sexes measure 45-63 centimeters long, weigh an average of 5.7 kilograms, but up to 7.5 kilograms (males perhaps being slightly larger).  Arms are 1.2 – 1.4 times as long as the legs.  Long fingers with opposable thumbs and big toes
• Coloration variable based on age and sex.  All are born with cream-colored fur.  At 2 years old, the fur changes to black and the animal develops the namesake white cheeks.  Upon reaching sexual maturity, females change back to the cream/tan color, losing much of the white on their cheeks, while males remain black.  Males have an upright tuft of fur on top of their heads.   Females often have a dark patch on the back of the head or nape of their neck.  Faces and the palms of the hands and soles of the feet are bare and black
• Genitalia of the adult male and adult female are fairly similar, making sexing on animals before they achieve their adult coloration difficult
• Highly arboreal, usually found in the canopy and rarely coming to the forest floor.  Travel through the trees by brachiating, swinging between branches using their long arms.  Fingers loosely hook around branches, enabling them to quickly make a hand-over-hand motion.  When on the ground, usually walk on their hind legs, holding their arms up or out for balance.  May reach speeds of up to 55 kilometers per hour and swing across trees up to 15 meters apart
• Live in small family units (up to 6, usually 3-4) of a breeding pair and their offspring.  Females are dominant to males; adult female is leader of the group, followed by female offspring, male offspring, and the adult male at the bottom.  Sleep in groups at night, holding onto one another
• Highly vocal, using calls to demarcate territories and as part of mating rituals.  Female usually initiates the call, making a series of 15—30 notes with an increasing pitch, followed by the male calling with rapidly changing frequency modulation.  Each cycle lasts for 20 seconds, can be repeated for several minutes.  In zoos, noted that pairs that call together frequently mate the most often.  Juveniles in a group sometimes join in when defending territory.  Pairs are the most vocal at dawn
• Home ranges of 0.3-0.4 square kilometers (75-100 acres), about three-quarters of which will be defended.  Males will only rarely physically fight one another over territory.  Aggression is communicated by gaping and showing canine teeth.  Typically, do not travel far, especially in the rainy season when fruit is plentiful.  May have to travel further in the dry season to find food.
• Important seed dispersers.  Forage throughout the day, feeding higher in the trees in the morning, moving to the lower layers in the afternoon.  AThe proportion of different foods in the diet changes based on seasonal availability, with fruit being preferred, but leaves making up the bulk of the diet during the dry season
• Until 1989, considered to be a subspecies of N. concolor (crested, or southern white-cheeked gibbon), which has a range immediately to the south of this species.  The two are most easily distinguished by the tuft of fur resembling a mohawk on N. leucogenys.  To differentiate the two, N. leucogenys is sometimes referred to as the northern white-cheeked gibbon
• Experiments in captivity have determined that they are capable of self-recognition
• Primary threat is habitat loss due to deforestation, both for timber and for agriculture (especially for palm oil plantations).  Also persecuted both by direct hunting (have been a source of meat for traditional communities, as well as playing a role in traditional medicines), as well as for the capture of infants for sale on the pet trade
• Depicted in Chinese poetry, artwork, and literature, especially during the Song Dynasty.  Admired for their grace and nobility, in contrast to macaques, which were seen as greedy.  Toaists believed that gibbons could live for hundreds of years and even turn into humans.  Although gibbons never naturally occurred in Japan, there is a popular Zen motif of a gibbon grasping at the reflection of the moon on the water.

Zookeeper's Journal: We joke about the smells, but it's often the sounds that I remember the most about the different zoos I worked at - and few sounds are more evocative than the ear-shattering whoops of the white-cheeked gibbon.  On my very first day in the zoo field, as a brand new volunteer at my city's zoo, what I remember the best were the gibbons.  I don’t remember seeing them that day, actually.  Instead, I remember sitting in the volunteer office, waiting for instructions, when suddenly the air was pierced by the cries of the pair of white-cheeked gibbons in the valley below.    Gibbons call most often in the early morning, before the zoo is open for the day - which means that staff and volunteers (and irate neighbors) are much more likely to experience it than visitors are.  It really may have been that call which told me that I was there, that I’d begun my zoo career.  When I did eventually make my way down to the gibbons later that week, I remember their songs, coupled with their easy, graceful movements as they swung around the enclosure.