If you want to learn about Mountain Gorillas, this page
contains lots of useful information about the habitat
and lifestyle of the Mountain Gorilla, as well as how
it is affected by changes to the rainforests.
The Mountain Gorilla (Gorilla beringei beringei) is one
of the three subspecies of the Eastern Gorilla. There
are two groups. One is found in the Virunga volcanic mountains
of Central Africa, within 4 national parks: Mgahinga,
in south-west Uganda; Volcanoes, in north-west Rwanda;
and Virunga and Kahuzi-Biéga, in the eastern Democratic
Republic of Congo (DRC). The other is found in Uganda's
Bwindi Impenetrable Forest. Some say that the Bwindi group
in Uganda is a 3rd species, though no description has
been finished.
The Mountain Gorilla has longer and darker hair than
other gorilla species, allowing it to live in hot or cold
weather and travel into areas where temperatures drop
below 32 degrees Fahrenheit (0 degrees Celsius). It has
chosen 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. Males usually weigh twice as much as the females,
and this subspecies is on average the largest of all gorillas.
Adult males have more pronounced bony crests on the top
and back of their skulls, giving their heads a more conical
shape. These crests anchor the powerful masseter muscles,
which attach to the lower jaw, or mandible. Adult females
also have these crests, but they are less pronounced.
Adult males are called silverbacks because a saddle of
gray or silver-colored hair develops on their backs with
age. 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 (350–500
lb). The tallest silverback recorded was a 1.94 m (6.4
ft) individual shot in Alimbongo, northern Kivu in May
1938 and the heaviest was a 1.83 m (6 ft) silverback shot
in Ambam, Cameroon which weighed about 266 kg (585 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
The Mountain Gorilla inhabits the Albertine Rift montane
cloud forests of the Virunga Volcanoes, ranging in altitude
from 2225 to 4267 m (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 a 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 small invertebrates (0.1%). Adult males can eat up
to 34 kg (75 lb) of vegetation a day, while a female can
eat as much as 18 kg (40 lb).
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
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. In its first few months of life, infant
Mountain Gorillas ride on their mother's backs. At an
earlier stage, the mother will almost constantly be holding
the infant. 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 ingests 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.
The Mountain Gorilla has no mating season and females
usually initiate mating behavior. 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 bear 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.
He is the center 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. Experienced silverbacks are capable of removing
poachers' snares from the hands or feet of their group
members.
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.
Behavior
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. The entire sequence
has nine steps: (1) progressively quickening hooting,
(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
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.
Fears
For reasons unknown, Mountain Gorillas that have been
studied appear to be naturally afraid of certain reptiles.
Infants, whose natural behavior is to chase anything that
moves, will go out of their way to avoid chameleons and
caterpillars. Koko, the gorilla trained in sign language,
is afraid of crocodiles and alligators, even though she
was born in captivity and has never seen them. They are
also afraid of water and will cross streams only if they
can do so without getting wet (ie. crossing over fallen
logs). Dian Fossey observed and noted the Mountain Gorilla's
obvious dislike of rain, as well.
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. Ruth Keesling succeeded Fossey
who was killed in 1985 and buried at the Karisoke Research
Station in Rwanda. Keesling took over the Digit Fund renaming
it the Dian Fossey Gorilla Fund Europe.
In April 2007 it was announced that a census of the Mountain
Gorillas in Uganda's Bwindi Impenetrable National Park
had recorded a 6% increase in population since a census
in 2002.
Conservation
Mountain Gorillas are threatened by poaching, loss of
habitat, and 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. Poaching for meat
is particularly threatening in regions of political unrest.
Most of the African great apes survive in areas of chronic
insecurity, where automatic weapons are readily available
and where there is a breakdown of law and order. The killing
of mountain gorillas at Bikenge in Virunga National Park
in January 2007 was a well documented case.
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.
War and civil unrest: Civil wars and weak governments
in central Africa, and in particular in the Congo, put
conservation efforts at risk from local militias and government
corruption. 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.
We are supporting the World Land Trust (WLT) - a conservation
charity involved in numerous projects worldwide. Particularly
relevant to this site is their work in helping to purchase
rainforest land to protect and preserve it.
You can Help to Buy Rainforest
and Save it by donating to the WLT to save some of
this land through a personal contribution or buying as
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If you have any photos, stories or drawings of mountain
gorillas, other animals or anything else to do with the
rainforest environment that you would like to see shown
on the site, please feel free to send them in. We always
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