Western lowland gorilla

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Physical features

• Male gorillas weigh 350-450 pounds, females 150-250 pounds, and newborns 3-5 pounds.

• Males stand 5’5” to 6’; females stand 4’7” to 4’11”.

• Gorillas reach physical maturity between 12 and 15 years.

• Western lowland gorillas have brownish gray hair often with an auburn colored crest. Mature males have silvering, which extends across the back to the rump and thighs. The females will show some silvering.

• The males’ heads are large and pointed due to the sagital crest. They have large jaw muscles for chewing tough vegetation. These muscles are attached to the skull at the sagital crest.

• Gorillas have very expressive faces, enabling them to communicate emotions to others in the family group. They also communicate using body language and vocalizations.

• The vision and perception of gorillas is similar to that of humans. Their ears are small and flat.

• Hearing is about the same as humans.

• Their nose is broad and flat with no nasal bone.

• Gorillas have large teeth with sharp canines. They are used for defense as well as breaking tough vegetation. They have 32 teeth.

• Their molars have complicated patterns of cusps and ridges to facilitate chewing.

• Gorilla hands and feet are large with leathery palms and soles, and broad, flat nails. Their hands are very dexterous and can pick up amazingly small, delicate objects. Their feet, like their hands, have opposable thumbs/toes.

• Gorillas usually walk quadrupedally (on all four limbs) with the fingers curled under, called knuckle walking. This develops calluses on the knuckles, preserving the sensitivity of the fingers.

Diet: Herbivore

• Wild – Leaves, shoots, stems, small amounts of wood, roots, flowers, fruits and grubs; occasionally insects when they are readily available.

• Zoo – A medley of fruits and vegetables. Apples, oranges, carrots, bananas, raisins, sweet potatoes, cabbage, collards and primate chow; Sugar cane is a favorite treat. Their morning vegetables are chopped up small, scattered in the exhibit. From there, the gorillas come outside and forage for their food which is a natural behavior; They also receive various types of browse: bamboo, banana leaves, mulberry, elm, willow, etc.

Reproduction

• Males are sexually mature at 9-10 years and females at 6-8 years.

• Nearly all female gorillas leave their family groups at maturity to join another group or a single male.

• In the wild they usually do not start breeding at this time; it is common for a few years to pass after sexual maturity before the female will breed. Estrus is approximately every 28 days and is 4 to 5 days long.

• Breeding can occur at any time of the year.

• Average gestation is 265 days. Labor can last from 1 to 4 hours.

• Babies are usually born singly; twins are very rare.

• Newborns will nurse for up to 4 years.

• They will give birth to another offspring about every 4 years.

Interpretive Information

• Gorillas communicate in many ways. Facial expressions, vocalizations and body gestures.

• The young play much like humans — they play tag and do somersaults.

• Grooming is a helpful way to keep clean and is also a social activity. It helps the gorillas feel close to one another.

• An adult male gorilla is as tall as a grown man when standing up straight.

• Gorillas are the largest primates and the males can weigh twice as much as females.

• The oldest captive gorilla, to date, still living, is 57 years old. The average captive Lifespan is likely to increase as our knowledge of gorillas increases.

• The wrinkles on a gorilla’s nose are like fingerprints. Different in each individual, they are used by researchers for identification.

• Of the great ape species, gorillas are the most terrestrial. This means that they primarily live on the ground, although they do occasionally climb trees to feed and nest.

• Gorillas are divided into two species (western and eastern) and four to five subspecies depending on whose taxonomy you follow. The two subspecies of western gorillas are Cross River gorillas (Gorilla gorilla diehli) and western lowland gorillas (Gorilla gorilla gorilla). The two subspecies of eastern gorillas include mountain gorillas (Gorilla beringei beringei), eastern lowland or Grauer’s gorillas (Gorilla beringei graueri), and Bwindi gorillas. Gorilla beringei beringei is found in two isolated subpopulations, Bwindi Impenetrable National Park, Uganda, and the Virunga Volcanoes region of Rwanda, Uganda, and Democratic Republic of Congo (DRC). While there has been some debate as to whether Bwindi gorillas should be considered as a separate subspecies (Sarmiento et al. 1996, Stanford 2001, Grubb 2003), they are considered here as one subspecies.

Social Behavior and Interaction

• Group size can vary from 2 to 25 individuals. Average group size is 5 to 10 individuals.

• One silverback is the dominant male leader and defender of the group. Groups are usually stable and keep the same leader for years. Groups can contain multiple silverbacks.

• There are 1 – 2 blackback males who are not of breeding age. They are offspring of the silverback and circulate on the fringes of the group acting as sentries. As they mature, blackbacks may challenge the silverback for dominance or leave the group.

• There are multiple adult females. They bond with the silverback and not with each other, although they do cooperate in defense. Females may leave their natal group upon maturation and join a lone male or small group. This transferring of both sexes is necessary to prevent inbreeding and to protect the gene pool. The silverback sires all infants and young.

Communication

• Twenty-five distinct vocalizations are recognized.

• Infants have three distinct vocalizations or “cries” which are similar to the cries of a human baby. They usually cry only when hurt or frightened. The mother’s response is immediate.

• Below are examples of vocalizations and behaviors associated with gorillas:

  • • Hooting: Can carry for a mile through the forest and is usually accompanied by display behavior such as chest beating, strutting and vegetation slapping.

    • Screams: Sounds of alarm or warning.

    • Belches: Deep rumblings of contentment, comfort or well-being.

    • Sharp Grunts: Used when discipline is required.

    • Whoop Barks: High-pitched barks denote curiosity.

    • Roars: Aggression

    • Chuckles: Playfulness

• Gorillas have a distinctive smell, which intensifies when they are nervous or frightened.

• It is impolite to stare in gorilla society — staring is a sign of hostility and is considered a challenge. When you are close to the gorillas turn your head and glance to the side.

• A silverback will often keep his group in line by screaming, throwing leaves and twigs in the air, standing on his hind legs and beating against his chest, and running sideways on all fours.

• Chest beating is a behavior primarily performed by male gorillas, usually at the end of a display, and is intended to intimidate intruding males or predators.

• Chest beating may also be used to communicate with solitary or group males and neighboring females. The sound echoes in the forest long distances.

• Female's chest beat infrequently. More often they beat their hands against the inside of their thighs.

• Chest beating is also done to communicate play behavior.

Zoo Habitat

• The habitats consist of almost 2 acres, broken up into 5 habitats; 1 habitat is off exhibit that the public cannot see. The habitats and indoor areas and designed such that the Gorilla Care Team can give the gorillas access to various configurations of indoor and outdoor areas.

• Double moats (10’ wide and 12’ deep) separate the habitats and ensure separation of the gorilla groups. The moats are dry because gorillas cannot swim and can drown in very little water. Gorillas do enjoy water when there is no fear of drowning, and have been seen splashing and playing in the pool or water feature.

• While the gorillas are outside, the holding areas are thoroughly cleaned; the walls and floors are scrubbed with brushes and disinfectant. Enrichment is provided to promote natural behaviors.

• The gorillas are offered bedding materials (such as hay, wood wool, and burlap) in their indoor area at night and nest with this material, replicating natural behavior.

• Habitats are numbered from left to right (1 to 5) from inside the holding area. If looking from the public viewing area, they are numbered 1 to 5 from right to left. Habitat 1 closest to the Asian Forest, Habitat 4 is closest to Scaly Slimy Spectacular, and Habitat 5 does not provide public viewing.

Updated 2023