Gorillas

Gorillas, the largest of the living primates, are ground-dwelling omnivores that inhabit the forests of Africa. Gorillas are divided into two species and (still under debate as of 2007) either four or five subspecies. Its DNA is 97%98% identical to that of a human, and are the next closest living relatives to humans after the two chimpanzee species.

Gorillas live in tropical or subtropical forests. Although their range covers a small percent of Africa, gorillas cover a wide range of elevations. 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). Lowland Gorillas live in dense forests and lowland swamps as low as sea level.

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.

Until recently there were considered to be three gorilla species: the Western Lowland Gorilla, the Eastern Lowland Gorilla and the Mountain Gorilla. There is now agreement that are two species with two subspecies each. More recently it has been claimed that a third subspecies exists in one of the species.

Primatologists continue to explore the relationships between various gorilla populations. The species and subspecies listed here are the ones upon which most scientists agree.
Genus Gorilla
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)
Eastern Lowland Gorilla (Gorilla beringei graueri)

The proposed third subspecies of Gorilla beringei, which has not yet received a full Latin designation, is the Bwindi population of the Mountain Gorilla, sometimes called the Bwindi Gorilla.

Gorillas move around by knuckle-walking. Adult males range in height from 165-175 cm (5 ft 5 in 5 ft 9 in), and in weight from 140200 kg (310440 lb). Adult females are often half the size of a silverback, averaging about 140 cm (4 ft 7 in) tall and 100 kg (220 lb). Occasionally, a silverback of over 183 cm (6 ft) and 225 kg (500 lb) has been recorded in the wild. However, obese gorillas in captivity have reached a weight of 270 kg (600 lb). Gorillas have a facial structure which is described as mandibular prognathism, that is, their mandible protrudes farther out than the maxilla.

Eastern gorillas are darker colored than Western gorillas, with Mountain gorilla being the darkest of all. Mountain gorillas also have the thickest hair. The Western lowland gorilla can be brown or grayish with a reddish forehead. In addition, gorillas that live in lowland forests are more slender and agile than the more bulky Mountain gorilla.

Almost all gorillas share the same blood type (B) and, like humans, have individual finger prints.

A silverback is an adult male gorilla, typically more than 12 years of age and named for the distinctive patch of silver hair on his back. A silverback gorilla has large canine teeth that come with maturity. Black backs are sexually mature males of up to 11 years of age.

Silverbacks are the strong, dominant troop leaders. Each typically leads a troop of 5 to 30 gorillas and is the center of the troop’s attention, making all the decisions, mediating conflicts, determining the movements of the group, leading the others to feeding sites and taking responsibility for the safety and well-being of the troop. Yonger mals called blackbacks may serve as backup protection.

Males will slowly begin to leave their original troop when they are about 11 years old, traveling alone or with a group of other males for 25 years before being able to attract females to form a new group and start breeding. While infant gorillas normally stay with their mother for 34 years, silverbacks will care for weaned young orphans, though never to the extent of carrying the little gorillas.

If challenged by a younger or even by an outsider male, a silverback will scream, beat his chest, break branches, bare his teeth, then charge forward. Sometimes a younger male in the group can take over leadership from an old male. If the leader is killed by disease, accident, fighting or poachers, the group will split up, as the animals disperse to look for a new protective male. Very occasionally, a group might be taken over in its entirety by another male. There is a strong risk that the new male may kill the infants of the dead silverback.

Food and foraging

Gorillas are omnivores, eating fruits, leaves, shoots, and sometimes insects which make up only 12% of their diet. Gorilla spend most of the day eating. Their large sagittal crest and long canines allow them to crush hard plant like bamboo. Lowland gorillas feed mainly on fruit while Mountain gorillas feed mostly on herbs, stems and roots.

Reproduction and lifespan

Gestation is 8? months. There are typically 3 to 4 years between births. Infants stay with their mothers for 34 years. Females mature at 1012 years (earlier in captivity); males at 1113 years. Lifespan is between 3050 years. The Philadelphia Zoo’s Massa set the longevity record of 54 years at the time of his death.

Gorillas are closely related to humans and are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language (see animal language for a discussion).

Tool use

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 Nouabal?-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. With training, in twentieth century carnival and circus acts, chimpanzees have been taught to operate simple motorbikes.

Studies
The word “gorilla” comes from the history of Hanno the Navigator, a Carthaginian explorer on an expedition on the west African coast. They encountered “a savage people, the greater part of whom were women, whose body were hairy, and whom our interpreters called Gorillae” . The word was then later used as the species name, though it is unknown whether what these ancient Cartheginians encountered were truly gorillas, another species of ape or monkeys, or humans.
19th century: The first scientific writings about gorillas dates back to the 1847 Proceedings of the Boston Society of Natural History, where Troglodytes gorilla is described, with a few other species following in the next couple of years.
Early 20th century: The next systematic study was not conducted until the 1920s, when Carl Akely of the American Museum of Natural History traveled to Africa to hunt for an animal to be shot and stuffed. On his first trip he was accompanied by his friends Mary Bradley, a famous mystery writer, and her husband. After their trip, Mary Bradley wrote On the Gorilla Trail. She later became an advocate for the conservation of gorillas and wrote several more books (mainly for children). In the late 1920s and early 1930s, Robert Yerkes and his wife Ava helped further the study of gorillas when they sent Harold Bigham to Africa. Yerkes also wrote a book in 1929 about the great apes.
Mid 20th century: After WWII, George Schaller was one of the first researchers to go into the field and study primates. In 1959, he conducted a systematic study of the Mountain Gorilla in the wild and published his work. Years later, at the behest of Louis Leakey and the National Geographic, Dian Fossey conducted a much longer and more comprehensive study of the Mountain Gorilla. It was not until she published her work that many misconceptions and myths about gorillas were finally disproved, including the myth that gorillas are violent.

Both species of gorilla are endangered, and have been subject to intense poaching for a long time. Threats to gorilla survival include habitat destruction and the bushmeat trade. In 2004 a population of several hundred gorillas in the Odzala National Park, Republic of Congo was essentially wiped out by the Ebola virus.. A 2006 study published in Science concluded that more than 5,000 gorillas may have died in recent outbreaks of the Ebola virus in central Africa. The researchers indicated that in conjunction with commercial hunting of these apes creates “a recipe for rapid ecological extinction” .

Gorillas have been a recurring element of many aspects of popular culture and media for at least the last hundred years. For example, gorillas have featured prominently in monstrous fantasy films like King Kong and pulp novels like Tarzan and Conan have featured gorillas as physical opponents to the titular protagonists.

Famous Gorillas:

Colo - female gorilla - born 22Dec56 to Millie and Baron Macombo (mom/dad). Colo is the first gorilla born in captivity and she’s still living where she was born, in Columbus, Ohio, where she and her ever-expanding family live.

Binti Jua & her daughter, Koola - Binti was born 17Mar88 in Columbus, Ohio to Lulu and Sunshine. After being hand-reared, Binti was finally introduced to other gorillas at Brookfield Zoo in Chicago. There, she kept to herself a lot, since it was difficult getting into the “clique” of Alpha and her daughters, Babs and Aquilina who were there at the time. Even so, Binti eventually met the old silverback, Abe, and had his only offspring, Koola, born 21Feb95. In the summer of 1996 when a little boy fell into the gorilla exhibit, Binti carefully cradled the boy and brought him to the keeper’s door, where she left him so he could be rescued. Binti became world-famous, and she deserves her celebrity, since - like Jambo before her - she helped more people see just how gentle, intelligent and remarkable gorillas really are!

Jambo - silverback gorilla. Jambo is famous for several reasons. He was born 17Apr61 in Basle, Switzerland and was the first baby gorilla in captivity to be raised by his own mother, Achilla (his father was Stephi). Jambo went to the Channel Island of Jersey, where he was a wonderful silverback and father to many offspring, who now reside in zoos virtually all over the world. Before the world knew Binti Jua, Jambo took care of another little boy who fell into his enclosure in the mid 1980’s. Home-video of the huge silverback gently stroking the unconscious little boy’s back were some of the first to show the masses how gentle gorillas really are. Sadly, Jambo died in 1992 and his keeper and best friend, Richard Johnstone-Scott, wrote a wonderfully moving book about his time with this superb silverback.

Koko - female gorilla - Koko is the world-famous “talking” gorilla, who speaks ASL - the sign language of the deaf. Recently she held a live conversation on AOL, using her human companions as translators. We were privileged to meet Koko in 1989, where Jane signed to her “I love gorillas” and Koko immediately signed back “Love gorillas YOU!” which we captured on video tape. Binti Jua is Koko’s niece!

Ivan in Tacoma, WA- silverback gorilla - born in Africa in 1964. Ivan is the famous “shopping mall gorilla” who spent most of his life alone in a shopping mall, without ever seeing another gorilla, until he came to Zoo Atlanta in the fall of 1994. When I took this photo, Ivan was just about to go into quarantine for his trip to Atlanta, and he was in a lot of pain from some dental problems. Even so, Ivan “painted” us a picture and was a very gracious, gorilla’s gorilla.

Ivan in Atlanta - A year later, I saw Ivan who had been sitting behind the rocks, ignoring the public, but came out to get a closer look when I purred and rumbled at him. Did he remember me?? Who knows? On subsequent visits to see Ivan in Atlanta, he usually will stroll out for a look-see, so I’d like to think he at least recognizes me as a friend of gorillas. Ivan is in with 2 female gorillas and in the spring of 1998 he had his first sexual experience, so maybe he’ll become a super dad like Willie B!

Snowflake - silverback WHITE gorilla - born in Africa in 1962 and now living in Barcelona, Spain. Also known as Copito de Nieve and Floquet de Neu, Snowflake is not an albino (or is he? See update below!). Although he has white hair, his eyes are blue, not pink. These photos were taken soon after one of his females had died, so his favorite female, Ndengue stayed nearby. Like many fair-skinned, blue eyed humans, Snowflake squints a lot in the bright sunlight and often people think he is grimacing or angry, which he is not. In fact, we were pleased to see how “normal” he behaved during our visit with him. Snowflake acted like a real gorilla’s gorilla and he’s sired over 20 babies, who have all turned out to be regular dark haired gorillas. Although most of his offspring did not survive, one now lives in Japan. Only one other white gorilla has been reported - seen in the wild as a baby with his/her mother, but s/he soon disappeared and was presumed dead.

On one of your gorilla haven pages, you state: “Snowflake - silverback WHITE gorilla - born in Africa in 1962 and now living in Barcelona, Spain. Also known as Copito de Nieve and Floquet de Neu, Snowflake is not an albino. Although he has white hair, his eyes are blue, not pink.” Actually, MANY albinos have blue eyes. It is an old wive’s tale that albinos must have pink eyes. Blue-eyed albinos are discussed by both the International Albinism Center and the National Organization for Albinism and Hypopigmentation, on their web sites.
So I wrote to my friends in Barcelona and got this reply, emailed on August 5th:

Hello Jane,
I am one of the veterinarians from Barcelona Zoo and have taken care of his health for the last 9 years. I got a message regarding albinism in snow fale (or “Copito de Nieve” as we say) from the Primate curator of BZ (Tereas Abello). There was a presentation in the American Association of Veterinary Dermatologist few years ago titled “Albinism in a Gorilla” by Ferrer, Fernandez, Castellels and Fernandez…if you want we can send you a reprint (it is a short communication). We conclude in that paper that snowflake is affected by a oculocutaneous albinism that could be equivalent to Type I-B or yellow albinism in human beings. This seems to be associated with reduced but sufficient levels of residual tyorinase activity to produce small amounts of pigment. His skin is totally white and the membranes are pale pink. hairs are also whiten although in some areas (head and shoulders) they were light yellow creamy. Iris is blue to gray and small amounts of pigment were found in the iridial stroma and in the retina. Pigment was absent in the posterior epithelium and the iris was fully translucent on globe transllumination. I hope this information is useful for your considerings, Regards,

Chicory - silverback gorilla - born 13May85 in New Orleans to mom Fanya and dad BomBom. Chicory came to Brookfield Zoo in Chicago as a youngster where he and Ndume became best buddies during the time I watched them (in the late 1980’s). . Chicory is famous since he had a brain tumor which human specialists operated on successfully in 1994. For some reason when I took this photo, Chicory was housed alone while the other gorillas were in the main exhibit. There was a 4 inch ledge where he could climb and hold onto to get a better view of people or things that interested him - it wasn’t very comfortable, so he couldn’t stay there for long. He hadn’t seen me for a while (and I’ve known him since he was about 3 years old) and he climbed up to sit on the tiny ledge. He’s looking at me almost like he’s asking where I’ve been and “asking” if I know when he is going to be let back in with his group! Sadly Chicory died unexpectedly and inexplicably August 22, 1998 at the age of 13 years. I will confess I am still easily brought to tears thinking about the loss of the potential this wonderful individual had, but I smile when I think of watching him grow from a toddler to a magnificent silverback..

TAXONOMY

Suborder: Anthropoidea
Infraorder: Catarrhini
Superfamily: Hominoidea
Family: Hominidae
Subfamily: Homininae
Genus: Gorilla
Species: beringei, gorilla
Subspecies: G. b. beringei, G. b. graueri, G. g. diehli, G. g. gorilla

Other names: gorilla (Finnish); gorille (French); gorilla (German); gorila (Spanish); bergsgorilla, gorilla, or l?glandsgorilla (Swedish); G. gorilla: western gorilla; G.g. diehli: Cross River gorilla; G.g. gorilla: western lowland gorilla; G. beringei: eastern gorilla; G.b. beringei: Bwindi, mountain, or Virunga; G.b. graueri: eastern lowland gorilla or Grauer’s gorilla
MORPHOLOGY

Western and eastern gorillas are more genetically distant from one another than are chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) (Butynski 2001). There are few striking physical differences between subspecies of gorilla, though differences in dentition and craniometric analyses reveal distinguishing morphological characteristics of each subspecies (Rowe 1996; Leigh et al. 2003). To some extent, even the inexperienced observer can distinguish the subspecies from one another. Mountain gorillas have significantly longer hair than their conspecifics, while western gorillas have brown, not black, hair on their heads, and eastern gorillas have longer faces and broader chests than western gorillas (Rowe 1996; Nowak 1999). 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) (Rowe 1996).

Gorilla gorilla gorilla

Spending the majority of their lives on the ground, the main locomotion pattern of gorillas is quadrupedal knuckle-walking although they do climb and spend limited amounts of time standing bipedally. Because of their sheer size, adult gorillas must climb near the main trunk of a tree or on large branches while juveniles and adolescents are more agile (Tutin et al. 1995; Rowe 1996).

Gorillas live between 30 and 40 years in the wild and up to 50 years in captivity (Stoinski pers. comm.).
RANGE

Gorillas are patchily distributed in east central and equatorial west Africa, separated by the Congo River and its tributaries. Western gorillas (including western lowland and Cross River gorillas) are found in a geographic area of about 709,000 km2 (273,746 mi2) covering parts of Nigeria, Cameroon, Central African Republic (CAR), Equatorial Guinea, Gabon, Republic of Congo, Angola, and far-western Democratic Republic of Congo (DRC). Cross River gorillas are found in only a 750 km2 (290 mi2) area in Nigeria and Cameroon, a pocket of land that is isolated from the majority of this region. Eastern gorillas (including mountain and eastern lowland gorillas) are found in portions of eastern DRC, Uganda, and Rwanda, in an area approximately 112,000 km2 (43,243 mi2), though mountain gorillas are restricted to two locations, Virunga Volcanoes where the borders of Uganda, Rwanda, and DRC meet, and Bwindi-Impenetrable National Park, Uganda (Nowak 1999; Butynski 2001; Sarmiento 2003).

Because of their great geographical separation, about 750 km (466 mi), western and eastern gorillas live in dramatically different habitats (Tutin & Vedder 2001). Even within-species habitat variation is quite great, from swamp to montane forest. Eastern gorillas live in submontane and montane forests from 650 to 4000 m (2132 to 13,123 ft)(Butynski 2001; Sarmiento 2003). Mountain gorillas live at the highest elevations, from 2200 to 4000 m (7218 to 13,123 ft), in the Virunga Volcanoes while eastern lowland gorillas occupy submontane forests from 700 to 2900 m (2297 to 9514 ft)(Butynski 2001). Where mountain gorillas exist, there are two rainy and two dry seasons per year, with average rainfall of 2000 mm (6.56 ft) per year (McNeilage 2001). The rainy seasons are from March until May and September to November while the dry seasons are June through August and December through February (McNeilage 2001; Robbins & McNeilage 2003). Temperatures range between 3.9° C (39° F) and 14.5° C (58° F), though they may reach 25.8° C (78.44° F) (Sarmiento 2003). Eastern lowland gorillas live in primary and secondary forests in both highland and lowland forests across their range. They occupy montane, bamboo, and lowland forests at elevations of 600 to 3308 m (1969 to 10,853 ft)(Ilambu 2001). There are two rainy seasons, the first lasting from March to June and the shorter lasting from September to December. There are also two dry seasons, the longer from June to September and the shorter from December until March (Yamagiwa et al. 1996).

Western gorillas live in lowland, swamp, and montane forests from sea level to 1600 m (5249 ft)(Butynski 2001; Sarmiento 2003). As their common name implies, western lowland gorillas live in lowland and swamp forests at elevations up to 1600 m (5249 ft) while Cross River gorillas inhabit low-lying and submontane forests at elevations from 150 to 1600 m (492 to 5249 ft)(Sarmiento 2003). Western lowland gorillas that live in mixed swamp forests experience one rainy and one dry season per year. Average rainfall is 1526 mm (5.01 ft) with the greatest amount of rain falling between August and November and diminishing during December through March (Poulsen & Clark 2004).
ECOLOGY

The considerable dietary differences between mountain, western, and eastern lowland gorillas impact home range size and social behavior. Despite these differences, though, all gorilla groups exhibit synchronized activities and, throughout the day, alternate between rest periods and travel or feeding periods (Stewart 2001). Mountain gorillas are folivores, feeding on leaves, stems, pith, and shoots of terrestrial herbaceous vegetation. They preferentially choose high quality, high protein, low fiber, and low tannin foods from a small number of species and incorporate little fruit into their diets (McNeilage 2001). Where bamboo is available, it is usually favored and they spend much time digging to unearth tender shoots. Because they depend on a readily available, easily accessed food source, there is little competition for resources between groups, their home ranges are small, typically between three and 15 km2 (1.16 and 5.79 mi2), and they move only 500 m (.311 mi) or less within a typical day (McNeilage 2001; Robbins & McNeilage 2003). Though they only utilize a few species in each habitat, mountain gorillas show wide dietary flexibility which enables them to occupy a wide variety of habitats within their range (McNeilage 2001).

The diet of eastern lowland gorillas is more diverse than the mountain gorillas’ and changes seasonally. While leaves and pith are staple parts of their diets, eastern lowland gorillas depend heavily on fruit (25 percent of their total diet), especially during the times of year when fruits are abundant. When they include insects in their diet, eastern lowland gorillas prefer ants (Yamagiwa et al. 1994). Eastern lowland gorillas generally use a small area for a few days and then travel long distances to another area. Eastern lowland gorillas that depend more heavily on fruit must travel farther in a day to find fruiting trees and have larger home ranges because of a relative scarcity of fruit. Their home ranges vary from 2.7 to 6.5 km2 (1.04 to 2.51 mi2) while their day range is between 154 and 2280 m (.096 and 1.42 mi)(Yamagiwa et al. 1996).

Western lowland gorillas have little dependable access to high quality terrestrial herbs across their range, but some areas are rich in aquatic herbs and they do eat herbaceous vegetation. Fruit is widely available, though dispersed, across their range, and is a central component of their diet, especially during times of fruit abundance (Tutin 1996; Doran & McNeilage 2001; Doran et al. 2002). Termites and ants are also important dietary staples. Western lowland gorillas have the largest home ranges and travel the farthest of all gorilla subspecies because of their reliance on fruit. The average distance traveled per day is 1105 m (.687 mi) and western lowland gorillas range over seven to 14 km2 (2.70 to 5.41 mi2) (Tutin 1996).

In some parts of their ranges, gorillas are sympatric with chimpanzees (Pan troglodytes) and dietary overlap in plant food and fruit is great. Where they occur together, gorillas and chimpanzees also have similar habitat use patterns and ecological competition is likely to occur (Kuroda et al. 1996). Though they share a similar niche, competition has not been recorded at any of the sites where the two apes overlap (McNeilage 2001).

Gorillas are vulnerable to predation by leopards (Panthera pardus), though direct documentation of attacks is difficult to obtain and rare. Evidence from leopard scat in areas where gorillas range is often the only means of confirming leopard predation, though even this is questionable as the large cats could simply be scavenging carcasses (Fay et al. 1995).

Content last modified: October 4, 2005

Written by Kristina Cawthon Lang. Reviewed by Tara Stoinski.

Gorillas Fight Human Invaders Using Weapons

This new discovery may help explain how early man learned to use natural objects as hunting and fighting weapons long ago.

Gorillas in the Cross River section of Cameroon were spotted throwing dirt clumps, stones, and sticks at humans they perceived as invaders. This was the first time the gorilla has been seen using tools aggressively.

Researchers believe that this is how early human ancestors learned to use tools as weapons, possibly against predators. However, they believe that the gorillas could have learned this from humans as well. Humans have thrown stones at the gorillas before, which may be how the animals learned the behavior.

Wildlife Conservation Society team member Jacqueline Sunderland Groves said:

“The area is largely isolated from other gorilla groups, but there are herdsmen on the mountain. In one encounter a group of gorillas threw clumps of grass and soil at the researchers while acting aggressively. Another gorilla threw a branch. A third encounter saw the gorillas throwing soil at a local man who was throwing stones at the apes.”

This observation, coupled with the sighting of a gorilla in the Congo using a stick as a tool to gauge water depth and cross a swamp, suggests the use of tools could have occurred before the evolutionary split of humans from today’s primates.