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Mountain Gorilla

2007 Schools Wikipedia Selection. Related subjects: Mammals

                iMountain Gorilla

                             Conservation status

   Critically endangered (CR)
            Scientific classification

   Kingdom:    Animalia
   Phylum:     Chordata
   Class:      Mammalia
   Order:      Primates
   Family:     Hominidae
   Genus:      Gorilla
   Species:    G. beringei
   Subspecies: G. b. berengei

                               Trinomial name

   Gorilla berengei berengei
   Matschie, 1914

   The Mountain Gorilla (Gorilla beringei beringei) is one of two
   subspecies of Eastern Gorillas. It is only found in the Virunga
   volcanic mountains of Central Africa, within three national parks:
   Mgahinga, in south-west Uganda; Volcanoes, in north-west Rwanda; and
   Virunga, in the eastern Democratic Republic of Congo (DRC). Some claim
   that the Bwindi population in Uganda's Bwindi Impenetrable Forest is a
   third subspecies, although no formal taxonomic description has been
   published.

   A census taken in 2003 has shown a 17% increase in population size
   since 1989. There are now a total of 380 gorillas in 30 social groups.
   However, the Mountain Gorilla continues to be considered critically
   endangered on the IUCN Red List of Endangered Species. It faces an
   extremely high risk of extinction in the wild due to habitat loss,
   poaching, human disease, and war.

Description

   The Mountain Gorilla has longer and darker hair than other gorilla
   species, enabling it to live at high altitudes and travel into areas
   where temperatures drop below freezing. It has adapted to a life on the
   ground more than any other non-human primate, and its feet most
   resemble those of humans. Gorillas can be identified by nose prints
   unique to each individual; researchers often use photographs and
   illustrations of noses for identification and monitoring.

   The Mountain Gorilla, like all gorillas, is highly sexually dimorphic,
   with males usually weighing twice as much as females. Adult males also
   have more pronounced bony crests on the top ( sagittal) and back (
   nuchal) of their skulls, giving their heads a more conical shape. These
   crests anchor the massive muscles of their large jaws. Adult females
   also have these crests, but they are much less pronounced.
   Nkuringo troop silverback, Bwindi, Uganda
   Enlarge
   Nkuringo troop silverback, Bwindi, Uganda

   Adult males are called silverbacks. When they reach sexual maturity, a
   saddle of gray or silver-colored hair develops on their backs. The hair
   on their backs is shorter than on most other body parts, and their arm
   hair is especially long. Upright, males reach 1.5–1.8 m (5–6 ft) in
   height, with an arm span of 2.25 m (7 ft 6 in) and weigh 204–227 kg
   (450–500 lb).

   The Mountain Gorilla is primarily terrestrial and quadrupedal. However,
   it will climb into fruiting trees if the branches can carry its weight,
   and it is capable of running bipedally up to 6 m (20 ft). Like all
   great apes other than humans, its arms are longer than its legs. It
   moves by knuckle-walking (like the Common Chimpanzee, but unlike the
   Bonobo and both orangutan species), supporting its weight on the backs
   of its curved fingers rather than its palms.

   The Mountain Gorilla is diurnal, most active between 6:00 a.m. and 6:00
   p.m. Many of these hours are spent eating, as large quantities of food
   are needed to sustain its massive bulk. It forages in early morning,
   rests during the late morning and around midday, and in the afternoon
   it forages again before resting at night. Each gorilla builds a nest
   from surrounding vegetation to sleep in, constructing a new one every
   evening. Only infants sleep in the same nest as their mothers. They
   leave their sleeping sites when the sun rises at around 6 am, except
   when it is cold and overcast; then they often stay longer in their
   nests.

Habitat and diet

   Adult male feeding on insects in rotting tree trunk
   Enlarge
   Adult male feeding on insects in rotting tree trunk

   The Mountain Gorilla inhabits the Albertine Rift montane cloud forests
   of the Virunga Volcanoes, ranging in altitude from 2225 to 4267 meters
   (7300-14000 ft). Most are found on the slopes of three of the dormant
   volcanoes: Karisimbi, Mikeno, and Visoke. The vegetation is very dense
   at the bottom of the mountains, becoming more sparse at higher
   elevations, and the forests where the Mountain Gorilla lives are often
   cloudy, misty and cold.

   The Mountain Gorilla is primarily an herbivore; the majority of its
   diet is composed of the leaves, shoots and stems (85.8%) of 142 plant
   species. It also feeds on bark (6.9%), roots (3.3%), flowers (2.3%),
   and fruit (1.7%), as well as larvae, snails and ants (0.1%). Adult
   males can eat up to 75 pounds of vegetation a day, while a female can
   eat as much as 40 pounds.

   The home range size (the area used by one group of gorillas during one
   year) is influenced by availability of food sources and usually
   includes several vegetation zones. George Schaller identified ten
   distinct zones, including: the bamboo forests at 2225–2804 m (7300–9200
   ft); the Hagenia forests at 2804–3353 m (9200–11000 ft); and the giant
   senecio zone at 3444–4267 m (11300–14000 ft). The Mountain Gorilla
   spends most of its time in the Hagenia forests, where gallium vines are
   found year-round. All parts of this vine are consumed: leaves, stems,
   flowers, and berries. It travels to the bamboo forests during the few
   months of the year fresh shoots are available, and it climbs into
   subalpine regions to eat the soft centers of giant senecio trees.

Reproduction

   Adult female breastfeeding
   Enlarge
   Adult female breastfeeding

   A newborn gorilla weighs about 1.8 kg (4 lb), and spends its first few
   months of life in constant physical contact with its mother. It begins
   to walk at around four or five months, and starts to put plant parts in
   its mouth between four and six months. At eight months it regularly
   ingest solid food. Weaning occurs around three years of age, although
   juveniles may remain with their mothers for years after that.

   Young male and female gorillas are considered infants from birth until
   three years of age, juvenile between the ages of about three and six,
   and subadult from six to about eight years old. Blackbacks are sexually
   immature males from around eight years until they have developed the
   silver saddle and large canines of maturity. Females begin to ovulate
   at 7 or 8 years of age, and have their first infant between the ages of
   10 and 12. Males, generally do not start breeding before the age of 15.
   Infant less than one month old
   Enlarge
   Infant less than one month old

   The Mountain Gorilla has no mating season and females usually initiate
   mating behaviour. The length of their menstrual cycle is about 28 days
   with 1-3 fertile days, and ovulation ceases for 3–5 years after
   reproducing. The length of gestation is eight and a half months.
   Females generally rear one infant every 6 to 8 years, and may leave
   only 2–6 offspring over a 40 year life span. Males that have harems of
   3–4 females increase their reproductive output by fathering 10-20
   offspring over 50 years.

Social structure

   The Mountain Gorilla is highly social, and lives in relatively stable,
   cohesive groups held together by long-term bonds between adult males
   and females. Relationships among females are relatively weak. These
   groups are nonterritorial; the silverback generally defends his group
   rather than his territory. In the Virunga Mountain Gorillas, the
   average length of tenure for a dominant silverback is 4.7 years.

   61% of groups are composed of one adult male and a number of females
   and 36% contain more than one adult male. The remaining gorillas are
   either lone males or exclusively male groups, usually made up of one
   mature male and a few younger males. Group sizes vary from five to
   thirty, with an average of ten individuals. A typical group contains:
   one silverback, who is the group's undisputed leader; one or two
   blackbacks, who act as sentries; three to four sexually mature females,
   who are ordinarily bonded to the dominant silverback for life; and from
   three to six juveniles and infants.

   Most males, and about 60% of females, leave their natal group. Males
   leave when they are about 11 years old, and often the separation
   process is slow: they spend more and more time on the edge of the group
   until they leave altogether.

   The dominant silverback generally determines the movements of the
   group, leading it to appropriate feeding sites throughout the year. He
   also mediates conflicts within the group and protects it from external
   threats. Experienced silverbacks are capable of removing poachers'
   snares from the hands or feet of their group members He is the centre
   of attention during rest sessions, and young animals frequently stay
   close to him and include him in their games. If a mother dies or leaves
   the group, the silverback is usually the one who looks after his
   abandoned offspring, even allowing them to sleep in his nest.

   When the dominant silverback dies or is killed by disease, accident, or
   poachers, the family group may be severely disrupted. Unless he leaves
   behind a male descendant capable of taking over his position, the group
   will either split up or be taken over in its entirety by an unrelated
   male. When a new silverback takes control of a family group, he may
   kill all of the infants of the dead silverback. This practice of
   infanticide is an effective reproductive strategy, in that the newly
   acquired females are then able to conceive the new male's offspring.
   Infanticide has not been observed in stable groups.

Behaviour

Aggression

   Severe aggression is rare in stable groups, but when two Mountain
   Gorilla groups meet, the two silverbacks can sometimes engage in a
   fight to the death, using their canines to cause deep, gaping injuries.
   For this reason, conflicts are most often resolved by displays and
   other threat behaviors that are intended to intimidate without becoming
   physical. The ritualized charge display is unique to gorillas. The
   entire sequence has nine steps: (1) hooting slow to fast, (2) symbolic
   feeding, (3) rising bipedally, (4) throwing vegetation, (5)
   chest-beating with cupped hands, (6) one leg kick, (7) sideways
   running, two-legged to four-legged, (8) slapping and tearing
   vegetation, and (9) thumping the ground with palms to end display.

Affiliation

   Young gorilla 2-3 years old
   Enlarge
   Young gorilla 2-3 years old

   The midday rest period is an important time for establishing and
   reinforcing relationships within the group. Mutual grooming reinforces
   social bonds, and helps keep hair free from dirt and parasites. It is
   not as common among gorillas as in other primates, although females
   groom their offspring regularly. Young gorillas play often and are more
   arboreal than the large adults. Playing helps them learn how to
   communicate and behave within the group. Activities include wrestling,
   chasing and somersaults. The silverback and his females tolerate and
   even participate if encouraged.

Vocalization

   Twenty-five distinct vocalizations are recognized, many of which are
   used primarily for group communication within dense vegetation. Sounds
   classified as grunts and barks are heard most frequently while
   traveling, and indicate the whereabouts of individual group members.
   They may also be used during social interactions when discipline is
   required. Screams and roars signal alarm or warning, and are produced
   most often by silverbacks. Deep, rumbling belches suggest contentment
   and are heard frequently during feeding and resting periods. They are
   the most common form of intragroup communication.

Research

   In October 1902, Captain Robert von Beringe (1865-1940) shot two large
   apes during an expedition to establish the boundaries of German East
   Africa. One of the apes was recovered and sent to the Zoological Museum
   in Berlin, where Professor Paul Matschie (1861-1926) classified the
   animal as a new form of gorilla and named it Gorilla beringei after the
   man who discovered it. In 1925 Carl Akeley, a hunter from the American
   Museum of Natural History who wished to study the gorillas, convinced
   Albert I of Belgium to establish the Albert National Park to protect
   the animals of the Virunga mountains.

   George Schaller began his 20 month observation of the Mountain Gorillas
   in 1959, subsequently publishing two books: The Mountain Gorilla and
   The Year of the Gorilla. Little was known about the life of the
   Mountain Gorilla before his research, which described its social
   organization, life history, and ecology. Following Schaller, Dian
   Fossey began what would become a 13 year study in 1967. Fossey made new
   observations, completed the first accurate census, and established
   active conservation practices, such as anti-poaching patrols.

Conservation

   Mother and child in Volcans National Park, Rwanda
   Enlarge
   Mother and child in Volcans National Park, Rwanda

   Mountain Gorillas are threatened by poaching, loss of habitat, and
   human disease.
     * Poaching: Mountain Gorillas are not usually hunted for bushmeat,
       but they are frequently maimed or killed by traps and snares
       intended for other animals. They have been killed for their heads,
       hands, and feet, which are sold to collectors. Infants are sold to
       zoos, researchers, and people who want them as pets. The abduction
       of infants generally involves the loss of at least one adult, as
       members of a group will fight to the death to protect their young.
     * Habitat loss: The forests where Mountain Gorillas live are
       surrounded by rapidly increasing human settlement. The humans' need
       for land, food, and timber encroaches on the gorillas' habitat
       through roads, slash-and-burn agriculture, and logging. The
       resulting deforestation confines the gorillas to isolated forest
       islands. Some groups may raid crops for food, creating further
       animosity and retaliation.
     * Disease: Humans and gorillas are genetically similar enough that
       gorillas are vulnerable to many of the same diseases as humans.
       However, gorillas have not developed the immunities to resist human
       diseases, and infections could severely impact the population.
       Habituated groups that are visited by tourists have the greatest
       risk.

   Conservation requires work at many levels, from local to international,
   and involves protection and law enforcement as well as research and
   education.
     * "Active conservation includes frequent patrols in wildlife areas to
       destroy poacher equipment and weapons, firm and prompt law
       enforcement, census counts in regions of breeding and ranging
       concentration, and strong safeguards for the limited habitat the
       animals occupy."
     * "Theoretical conservation seeks to encourage growth in tourism by
       improving existing roads that circle the mountains, by renovating
       the park headquarters and tourists' lodging, and by the habituation
       of gorillas near the park boundaries for tourists to visit and
       photograph."
     * Community-based conservation supports African ownership, provides
       education on the personal as well as environmental benefits of
       preserving protected areas, and encourages local people to take
       pride in and assume some of the responsibility for the protection
       of their parks.

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