Gorilla, Western Lowland


Gorilla gorilla gorilla


Western gorillas are exceptionally large and powerful primates.  Gorillas have dark brown to black fur and black skin. Dominant adult males, called silverbacks, have a prominent sagittal crest and striking silver coloration from their shoulders to rump. Males and females are sexually dimorphic, with males weighing up to 181 kg (400 lb) in the wild and 227 kg (500 lb) in captivity and measuring, on average, 1700 mm, while females weigh between 72 and 98 kg (159 and 216 lb) and measure, on average, 1500 mm (4.92 ft). Hands are proportionately large with nails on all digits and very large thumbs. Limbs are plantigrade and pentadactyl. The main locomotion pattern of gorillas is quadrupedal knuckle-walking although they do climb and spend limited amounts of time standing bipedally. 

Family

Hominidae

Order

Primates Suborder: Haplorrhini

Class

Mammalia

Range

Nigeria, Central African Republic, Equatorial Guinea, Gaboon, Republic of Congo, Angola and Demacratic Republic of Congo.

Habitat

Western gorillas live in lowland, swamp, and montane forests from sea level to 1600 m (5249 ft) As their common name implies, western lowland gorillas live in lowland and swamp forests at elevations up to 1600 m (5249 ft).

Life Expectancy

In the wild, gorillas live an average of 35 to 40 years. In captivity, gorillas may reach 50 years of age.

Sexual Maturity

Females become sexually mature between 6-9 years of age. Males reach sexual maturity between 9-12 years of age.

Diet

In the wild, as herbivores, the main diet of western lowland gorilla groups is roots, shoots, fruit, wild celery, tree bark and pulp which is provided for in the thick forests of central and west Africa. They may also eat insects from time to time. In the Zoo, they are fed a scientifically developed commercially produced foraging chow, variety of fruits and vegetables, and several types of browse and forage items.

Status

IUCN – Critically Endangered; CITES - Appendix I; USF&WS – Endangered; AZA - red SSP

Behaviors

Gorillas live in groups of one adult male and several females. They play, sleep and eat within this structured family group. The dominant silverback male leads the group. He regulates what time they wake up, eat, and go 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. Every night before dusk gorillas make a nest bed on the ground or in a tree. When males reach sexual maturity they become solitary or find other males to form bachelor groups. Western gorillas infrequently stand upright, and walk in a quadrupedal fashion, with hands curled and knuckles touching the ground. Walking quadrupedally requires long arms, and the arm span of gorillas is larger than their standing height. There is no set time of the year to give birth. A female may have between 3-6 offspring in a lifetime. Only the silverback is allowed to mate with the adult females in his group. Females menstruate every 28 days. The western lowland gorilla has a gestation period of 8-9 months. The offspring are born helpless and weigh about 3-5 pounds. They grow at twice the rate of a human baby and are able to crawl and cling to their mother by the age of 3 months. Young gorillas nurse for 3 to 4 years. Females give birth at about four-year intervals, beginning when they are approximately ten years of age. However, a high mortality rate means surviving offspring are produced only once every 6 to 8 years. Males, because of physical competition for mates, only rarely breed before the age of 15. Females provide the young with transportation, food, and socialization. They protect their young within the group. Males do not typically interact much with the young, although they do protect their offspring by defending the social group against potentially infanticidal males who might wish to take over control of the group. The western lowland gorilla is characterized as a quiet, peaceful and a very non-aggressive animal. 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 will rear his head back violently several times and drop on all fours, charging toward the intruder. They merely pass them by and usually do not hit the intruder. This demonstration of aggression maintains order among separate troops and reduces the possibility of injury. Overlapping troops in the wild rarely have confrontations. The western lowland gorilla is predominantly folivorous, feeding primarily on leaves and stems rather than fruits. A silverback can eat up to 6.5 pounds of vegetation a day. Gorillas build day and night nests of branches and leaves for cushion on the ground or in trees. Lightweight individuals can be seen swinging from tree to tree by their arms (brachiation). Mutual grooming is not as common in gorillas as it is in other primate species. Gorillas communicate using calls, facial expressions and physical postures, and through tactile means. Scents may play some role in communication in these animals. The following observations were made by a team led by Thomas Breuer of the Wildlife Conservation Society in September 2005. Gorillas are now known to use tools in the wild. A female gorilla in the Nouabalé-Ndoki National Park in the Republic of Congo was recorded using a stick as if to gauge the depth of water whilst crossing a swamp. A second female was seen using a tree stump as a bridge and also as a support whilst fishing in the swamp. This means that all of the great apes are now known to use tools. In September 2005, a two and a half year old gorilla in the Republic of Congo was discovered using rocks to smash open palm nuts inside a game sanctuary. While this was the first such observation for a gorilla, over forty years previously chimpanzees had been seen using tools in the wild, famously ‘fishing’ for termites. It is a common tale among native peoples that gorillas have used rocks and sticks to thwart predators, even rebuking large mammals. Great apes are endowed with a semi-precision grip, and certainly have been able to use both simple tools and even weapons, by improvising a club from a convenient fallen branch.

Adaptions

Gorillas usually walk on all fours. They have a very stocky build, with a broad chest. The face, ears, hands, and feet are bare, arms are longer than the legs. In comparison to the mountain gorilla, the western lowland gorilla has a wider and larger skull. Also, the big toe of the western lowland gorilla is spread far apart from the alignment of his other four toes compared to the alignment of the mountain gorilla. They are mostly terrestrial, though they can climb well enough. Adult males spend most of their time on the ground because of their weight. Marked sexual dimorphism between males and females is critical in group structure and mating. Large males, with large body size, canines, and jaw musculature, have increased physical and social power within the group.

Special Interests

Western lowland 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. They do not groom each other and appear to be irritated by grooming and bathing. Primatologists continue to explore the relationships between various gorilla populations. The species and subspecies listed here are the ones upon which most scientists agree: Western Gorilla (Gorilla gorilla), Western Lowland Gorilla (Gorilla gorilla gorilla), Cross River Gorilla (Gorilla gorilla diehli), Eastern Gorilla (Gorilla beringei), Mountain Gorilla (Gorilla beringei beringei), and Eastern Lowland Gorilla (Gorilla beringei graueri). The proposed third subspecies of Gorilla beringei, which has not yet received a trinomen, is the Bwindi population of the Mountain Gorilla, sometimes called the Bwindi Gorilla. The closest relatives of gorillas are chimpanzees and humans, from which gorillas diverged about 7 million years ago. Human genes differ only 1.6% on average from their corresponding gorilla genes in their sequence, but there is further difference in how many copies each gene has. Western gorillas have been used in medical study of human diseases and behavioral, linguistic, and psychological studies. The mental capacity of gorillas is still being explored. Western gorillas show more persistence and memory retention in problem solving studies than do their, more excitable, near relatives, chimpanzees (Pan). Western gorillas are more likely to perform a task out of interest than to earn a reward. The lives of gorillas in the wild was enigmatic until American zoologist George B. Schaller observed the species for many years and published a pioneering study titled, “The Mountain Gorilla: Ecology and Behavior” (1963). American Diane Fossey followed his work by studying and living among mountain gorillas from 1963 until her death in 1985 at the Karisoke Research Center, which she had established in Rwanda in 1967.

Folklore

Even in antiquity, reports filtered into Mediterranean cities about large apes sighted and even captured. Reports described gorillas as “exceedingly ferocious and always offensive in their habits” and encounters were described as “often fatal to the hunter.” The American physician and missionary Thomas Staughton Savage first described the Western Gorilla (he called it Troglodytes gorilla) in 1847 from specimens obtained in Liberia. The name was derived from the Greek word Gorillai (a “tribe of hairy women”) described by Hanno the Navigator, a Carthaginian navigator and possible visitor (circa 480 BC) to the area that later became Sierra Leone. Paul Du Chaillu, reportedly the first person known to shoot a gorilla, described the encounter as “reminding me of nothing but some hellish dream creature – a being of that hideous order, half-man half-beast . . .in some representations of the infernal regions – an ogre killed at six yards range.”

Conservation

In the 1980s, a census taken of the gorilla populations in equatorial Africa was thought to be 100,000. Researchers adjusted the figure after years of poaching and deforestation had reduced the population to approximately 50,000. Surveys conducted by the Wildlife Conservation Society in 2006 and 2007 found more than 100,000 previously unreported gorillas have been living in the swamp forests of Lake Tele Community Reserve and in neighboring Marantaceae (dryland) forests in the Republic of the Congo. With the new discovery, the current population of Western Lowland Gorillas could be around 150,000–200,000. However, the gorilla remains vulnerable to Ebola, deforestation, and poaching. Gorillas are hunted illegally for their skins and their meat, which is served in restaurants of large towns.

Jacksonville Zoo History

The first western lowland gorillas for which we have any records were four silverbacks named “Lash”, “Rumplestiltskin”, “Quito”, and “Ben”. They arrived in February 1998. After the loss of one of our silverback Ben in 2006, we had the three males living in two groups until 2009. In Nov. 2009 we received a pair of female gorillas from the Lincoln Park Zoo named “ Bulera” and “Madini”. From 2009 to 2013 gorillas were managed in two groups. A harem group which consisted of Quito, Bulera and Madini, who shared their exhibit with a group of Guereza colobus monkeys. JZG also managed 2 silverbacks Lash and Rumpelstillskin making a bachelor group. After the loss of the silverback Quito in 2013, JZG integrated both groups into one unique family group consisting of two silverbacks and two females. In 2014 JGZ received a breeding recommendation and in 2015 JZG integrated a new female named “Kumbuka” from Miami.

Exhibit

Great Apes Exhibit Area