Geographic RangeWestern lowland gorillas, Gorilla gorilla gorilla, are found in the tropical forests of western Africa, from southern Nigeria to the Congo River.
Mountain gorillas are found along the Virunga Volcanic range and in mountainous parts of Congo.
Physical DescriptionSize
Males average 6 ft
Females average 5ft..
Arm Span (fingertip to fingertip)
Adult male: Approximately 8 feet (2.4 m)
Adult female: Approximately 6.5 feet (2 m)
Weight
Adult male weight: 350-600 pounds (157-273 kg)
Adult female weight: 150-300 pounds (66-136 kg)
Gorillas can weigh from 135 to 175 kg. Males are significantly larger than are females. They have a broad chest, muscular neck, and strong hands and feet. Short, thin, grey-black to brown-black hair covers the entire body except the face. A thick ridge of bone juts out above the eye, and the nostrils are flared. In comparison to mountain gorillas, western lowland gorillas have wider and larger skulls. Also, the big toe of western lowland gorilla individuals is spread far apart from the alignment of the remaining four toes, when compared to the alignment in mountain gorillas.
BehaviorGorillas live in groups of one fully adult male and several females. They play, sleep, and eat within this structured family group. The dominant male, often called the silverback male, leads the group. He regulates what time the group wakes up, eats, and goes to sleep.
Gorillas are most active in the morning. They wake up just after sunrise to search for food, and then they eat for several hours. During midday, adults usually nap while the young wrestle and play games that to observers resemble games played by human children such as "Follow the Leader" and "King of the Hill". After their midday nap, they search for food again. Before dusk, each gorilla makes its own nest bed on the ground or in vegetation, such as in an available tree.
Some males become solitary after they have reached adulthood. Nevertheless, a new troop can be easily formed when one or more non-related females join a lone male.
Gorillas are characterized as quiet, peaceful, and non-aggressive animals. They never attack unless provoked. However, once provoked, an adult male protecting his group will attempt to intimidate his aggressor by standing on his legs and slapping his chest with cupped hands, while roaring and screaming. If this elaborate display is unsuccessful, and the intruder persists, the male rears his head back violently several times. Then he will drop on all fours and charge toward the intruder. In general, when males charge they do not hit the intruder, only running close to them. This demonstration of aggression maintains order among separate troops and reduces the possibility of injury. Overlapping troops in the wild rarely have confrontations. (From 'Gorillas in the Mist' by Dian Fossey - Gorillas have actually been known to attack intruders. If the intruder runs, the gorilla(s) will see this as a chase and will beat and bite the intruder upon catching them.)
Gorillas thrive on their secure family structure, and they require companionship and attention in order to live. It was said that the first gorillas captured died of loneliness.
A troop will remain in a territory of 9 to 14 square km, rarely disturbing other overlapping troops.
Communication and PerceptionCommunication in primates involves many different modalities. Visual signals, such as body postures and facial expressions, convey the state of an individual to its conspecifics.
In addition, tactile communication, in the form of grooming, play, and mating, allows these apes fo communicate.
Olfactory communication, although not reported, is likely to be of importance during mating, as well as between mothers and their offspring.
Finally, vocal communication is common to most primates.
Food HabitsWestern lowland gorillas are herbivorous, feeding on fruit, shoots, bulbs, a little tree bark, and leaves. While in captivity, they also prefer foods such as baked sweet potatoes or yams, baked bananas, oranges, other raw fruits and berries, milk, egg, dry cereal, and raisins. A silverback can eat up to 3 kg of vegetation a day. Contrary to popular belief, only captive gorillas have been seen to eat meat.
ImagesSentryIllustrationSilverback close-upMountain gorilla - silverbackMountain gorilla - silverback in mid chargeMountain gorilla - male recliningMountain gorilla - male roar(Information courtesy of
Animal Diversity Web)
SOCIAL BEHAVIORThe gorilla has a unimale social system and a polygynous mating system. The basic group is composed of one mature silver-back male (the leader of the group), one subadult or black-back male (about 8 to 12 years old), three adult females, and two to three young (less than 8 years old). Both males and females emigrate from their natal troop. Grooming occurs between the silver-back and the adult females and the juveniles and the silver-back and between juveniles. Males will only stay in their natal group if they are likely to be able to mate with females. This occurs if the silver-back male is old and is ready to die soon, the son will inherit the group. Males generally become solitary until about the age of 15 when they are strong enough and have a home range to start a group of their own. Lone silver-back males will challenge a resident silver-back and try to get the females to come with him. The resident male does actively prevent the females from going with him, but rather performs elaborate displays to keep the lone silver-back from approaching.
VOCAL COMMUNICATIONroar: This call is given by silver-back and large black-back males. This call is low in pitch and is an outburst of sound through the open mouth. This call is given when the individual is under stress or threat, and the individual may give false charges and short lunges. The group hides behind the silver-back when hearing this.
wraagh: This call is also an outburst, but not deep as the roar, and is monosyllabic in nature. This call is mostly emitted by the silver-back male. This is emitted when the individual is experiencing sudden stress, and group members scatter when hearing this call.
hoot series: This call is low-pitched and consists of a series of "hoo-hoo-hoos". This call is emitted by the silver-back male. This call is given in response to seeing members from another group, and it is used to maintain group spacing. This is given before chest- beating.
scream: This call is loud and is a shrill sound repeated many times. This call is emitted by all gorillas, and is given when the individual is upset or fighting with other gorillas.
question bark: This call consists of a short series of three notes, the first and third being lower in pitch than the second. Mostly this is given by the silver-back male, and he emits this when he discovers someone that was concealed or another individual that is making noise but can not be seen.
cry: This is given by infants, and is a response to extreme distress. This is a wail-like call that can build up to a shriek.
chuckle: This is a rasping sounding call, and is given by infants during play.
belch vocalizations: This call is given by all gorillas, generally when they are stationary, and generally communicates contentment. These noises consist of purring, humming, rumbling, crooning, moaning, and soft-grunting noises.
pig grunts: This call consists of a series of short guttural noises. This call is given by adult males and females, and communicates mild aggression. This call is emitted when the adult wants access to preferred foods or right of way.
whine: This call is given by infants and adult males when they are being left behind.
copulatory panting: This is a series of "o-o-o-o" sounds that are loud and low-pitched. This is given by the males during copulation.
VISUAL COMMUNICATIONchest-beating: This behavior is done by all gorillas and the either one or two open-fist hands are clapped against the chest. Adult males produce a sound when doing this because of air sacs they have which are located on both sides of their throat. For the adult male this is a threat display.
strutting walk: This is a rigid walk with arms bowed and the hair bristled so that the individual looks bigger. The individual makes short steps and has the side facing the receiver and only looks at the receiver but for a few glances. This is a dominance display and is mainly performed by silver-back males especially when a lone silver-back is attempting to lure a female away from the group.
staring: This where the sender has its eyes fixed on the receiver, the eyebrows are lowered, the head is angled down, and the lips are parted and pursed. This communicates aggression or annoyance.
tense-mouth face: This is like staring but the gums and teeth are displayed having the lips curled back. This is a threat display for potential predators, mostly given by adult males, and is often accompanied by a mock charge and scream and roars.
pout face: This is where the lips are pursed, mouth is slightly parted or compressed, and the eyebrows are raised. This is most often given by infants when their mothers leave them or they do not receive what they want, it is a display of light distress.
open-mouth grimace: This is where the mouth is wide open, the corners of the mouth are drawn back, the eyebrows are raised, the head is tilted back a little, and the eyes move back-and-forth. This is a fear display.
play face: This is where the mouth is open but not showing the teeth or gums. This is seen during pla(Information courtesy of
Primates.Com)
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