Gorillas

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SOME OF THE INFORMATION I GOT FOR THIS PAGE CAME FROM

THE SEAWORLD SITE.

Scientific Classification

A. Class--Mammalia.
B. Order--Primates.
The primate order encompasses 11 families, including lemurs, monkeys, apes, marmosets, the great apes, and humans, among others.
C. Family--Pongidae.
The great ape family includes the gorilla, chimpanzee, bonobo, and orangutan.

D. Genus, species--Gorilla gorilla.
This genus includes three subspecies of gorilla, which are distinguished by their physical differences and their distribution in Africa. The western lowland gorilla is Gorilla gorilla gorilla, the eastern lowland gorilla is G. g. graueri, and the very rare mountain gorilla is G. g. beringei&127;.
E. Ancestry.
1. The earliest recognized primates first appear in the fossil record about 70 million years ago (Macdonald, 1985).
2. The fossil record suggests that relatives of the lesser and greater apes diverged by 20 million years ago (Macdonald, 1985).
3. Both the fossil record and biochemical research indicate that the chimpanzee is the gorilla's closest relative (Dixson, 1981).

Habitat and Distribution

A. Distribution.
1. The western lowland gorilla is found in the African countries of Cameroon, Central African Republic, Gabon, Congo, and Equatorial Guinea. The easternmost range of the western lowland gorilla is the Oubangui River (Fay, 1989).
2. The eastern lowland gorilla is found in eastern Zaire.
3. The mountain gorilla is found within limited mountainous regions of Zaire, Rwanda, and Uganda at altitudes of 1,650 to 3,790 m (5,413-12,435 ft.).
4. Large rivers probably act as geographical barriers between the western and eastern populations of gorillas.
B. Habitat.
1. Western lowland gorillas inhabit tropical rain forests, forest edges and clearings, riverine forests, swamps, and abandoned, cultivated fields.

Lowland gorillas at Busch Gardens, Myombe Reserve.

2. Though mainly terrestrial because of their large size, young gorillas regularly climb trees to forage and play, and even silverbacks (adult males) cautiously climb as high as 30 m (98.5 ft.) to forage for seasonal fruits (Williamson, 1990).
3. While preliminary studies placed western lowland gorillas in sunny, dry secondary growth or open forests where dense vegetation thrives, recent field work revealed that these gorillas use all forest types, including swampy areas, for nesting and feeding (Fay, 1989).
An activity appropriate for 4-8 grade
C. Migration.
1. A western lowland gorilla band travels within a home range averaging 5.6 to 6.8 sq. km (2.2-2.7 sq. mi.). Gorillas do not display territorial behavior, and neighboring groups often overlap ranges (Dixson, 1981).
2. The band usually favors a certain area within the home range because of terrain but seems to follow a seasonal pattern depending upon the availability of ripening fruits.
3. Gorillas normally travel 0.5-1.0 km (0.3-0.6 mi.) per day (Dixson, 1981).
D. Population.
1. Accurate population estimates for gorillas are difficult to establish because their range has not been thoroughly surveyed.
2. All gorilla populations are in decline. Through the Endangered Species Act (1973), the U.S. Fish and Wildlife Service lists and protects all gorillas as endangered. The three subspecies are also protected by strict trade regulations established by the Convention on International Trade for Endangered Species (CITES), a coalition of over 100 countries.
3. According to current estimates, roughly 50,000 gorillas remain in Africa. While western lowlands are the most abundant, there are only about 2,500 eastern lowland gorillas and 600 mountain gorillas.

Physical Characteristics and Special Adaptations

  A. Size.
Adult female gorillas tend to be shorter than adult males, and weigh only half as much. Females average 1.4 m (4.6 ft) and 90 kg (198 lb.). Males average 1.7 m (5.6 ft.) and 180 kg (397 lb.).
  B. Body.
1. A gorilla has a stocky build with a broad, shallow chest, a short trunk and longer arms than legs. The elongated   arms indicate the gorilla's tree-dwelling ancestry even though it is now primarily terrestrial.
2. The thumb and big toe oppose the other digits, enabling gorillas to grasp and/or manipulate objects.
3. Normal locomotion is quadrupedal (using all four limbs). Gorillas knuckle-walk by curling up their fingers and walking on the soles of their feet (Schaller, 1963).4.   Bipedal (two-legged) locomotion is rare. Gorillas generally travel no farther than about 6 m (20 ft.) on two legs. The upright stance is used for chest-beating, to observe something, or to reach an object (Schaller, 1963).
5. Like all apes, gorillas do not have a tail.
6. The gorilla's pot-bellied appearance comes from an enlarged intestine needed to accomodate and digest the bulky food items on which this great ape feeds (Maple, 1982).
  C. Head.
1. The head of a gorilla is massive, with a bulging forehead overhanging the eyes and a bony sagittal crest on top. The crest is especially noticeable in adult males and supports the large temporal muscles needed to grind vegetation.
2. The faces of individual gorillas vary from flat to prominent, round to oval.
3. Their nose regions are very distinctive and are used to distinguish individual animals in the field (Schaller, 1963).
4. The   ears lie close to the skull.
5. The small   eyes are usually dark brown.
6. Gorillas have 32   teeth. The canines are strongly developed, and the male's canines are much larger than the female's. The molars are quite large to process the amount of vegetation gorillas eat.
  D. Hair.
1. Adult gorillas lack hair on the fingers, the soles of the hands and feet, and armpits. Hair is sparse on the upper chest, especially on older males.
2. The skin of a gorilla is   dark and covered with black to reddish-brown hair. As the animals mature, the hair turns gray. Males acquire silver-gray saddles across their backs and upper thighs at sexual maturity, earning them the name silverback.
3. Newborns initially have pinkish-gray skin which quickly darkens. They frequently have a white rump patch until a few years old.
  E. Learning capacity.
1. All great apes exhibit a capacity for complex learning. In behavioral research facilities, some gorillas have learned sign language and formed very simple sentences to communicate with people.
2. Chimpanzees have been observed creating tools from their environment and then using them to accomplish certain tasks such as probing for termites with sticks or gathering water for drinking with crumpled leaves. Young chimps learn these behaviors from watching other chimps. Gorillas have not been observed making or using tools in the wild.

Senses

A gorilla's senses are probably comparable to a human's but they have not been studied extensively.
  A. Hearing.
Since visibility is often restricted by dense vegetation, hearing is important for gorillas to locate one another and to detect danger. Gorillas seem to respond to unusual noises that are not a part of their normal activity (Schaller, 1963). See communication.
  B. Eyesight.
1. Gorillas have good eyesight which is used for finding and identifying food and to spot movement. As daytime herbivores they probably have color vision, a useful adaptation for finding ripening fruits in treetops (Dixson, 1981).
2. Gorilla eyes focus closer than human eyes, so gorillas appear nearsighted while studying grooming matter and food items closely (Schaller, 1963).
  C. Smell.
1. Gorillas have a good sense of smell and are able to detect strong odors in the environment such as human sweat or the musk of an unknown gorilla.
2. Subordinate males use a female's odor to determine her reproductive status (Dixson, 1981).

Diet and Eating Habits

A. Diet.
1. Western lowland gorillas eat more fruit than the other subspecies; it is readily available within the lower elevations of their range. They are selective feeders that utilize the fruits, stems, flowers, shoots, bulbs, bark, leaves, and pith of over 200 plant species.
2. Analysis of dung suggests that gorillas choose their favorite fruits for the sugar content, unripe seeds of certain fruits because of low fat content, the stems of plants for fiber, and new leaves for protein (Rogers, 1990).
3. Gorillas seldom drink water; their succulent food items provide enough dietary water.
4. Gorillas have never been observed hunting or feeding on any animals other than invertebrates such as termites and ants.
5. Because gorillas are selective eaters, they never strip a feeding site bare. Adequate vegetation remains for regrowth.
B. Method of Feeding.
A gorilla uses its hands and mouth to collect and prepare food.

Reproduction

  A. Sexual Maturity.
1. Female gorillas reach sexual maturity at about eight years and generally conceive for the first time at 10 to 11 years.
2. Males mature at about 12 years but seldom breed successfully before 15 years.
  B. Reproductive Cycles.
1. The gorilla menstrual cycle is about 30 to 32 days long. Ovulation occurs mid-cycle during a 2 to 3 day period.
2. Labial swelling during estrus is minimal, especially in comparison with a chimpanzee.
  C. Breeding.
1. Gorillas   breed throughout the year.
2. Immature males check a female for olfactory cues to estrus. A receptive female solicits the dominant silverback by special glances and touches.
3. Only the dominant silverback breeds with adult females in estrus. He allows subordinate males to court immature or pregnant females.
  D. Captive Breeding.
1. As recently as 20 years ago, gorillas did not reproduce well within zoological parks. Now that zoos understand more about gorilla behavior and can provide facilities that meet their social requirements, western lowland gorillas in zoological parks are successfully breeding.

Birth and Care of Young

  A. Gestation
Gestation for gorillas is about 250 to 285 days.
  B. Frequency of Births.
1. The interval between births is about 4 to 4.5 years if the offspring survives.
2. Mortality for young gorillas is about 40% because of injury, illness, and the long period of dependency on the mother that also faces these risks (Schaller, 1963). Over a lifetime, females usually raise three young to maturity.
  C. Gorillas at Birth.
A newborn gorilla weighs about 1.4 to 1.8 kg (3-4 lb.).
  D. Care and Development of Young.
1. Newborn gorillas are totally dependent on their mother for care and are clutched belly-to-belly for close contact for the first few months. At about two months they have developed enough strength and coordination to cling to their mother's hair unsupported 50% of the day.
2. An infant gorilla begins crawling at about nine weeks, riding on its mother's back at about 16 weeks, walking at about 35 weeks, and wandering among group members at about one year.
3. Gorilla babies develop physical skills about twice as fast as human babies.
4. Juveniles are weaned at about 2 1/2 years and begin building their own nests for sleeping.
5. Silverbacks are tolerant parents that successfully rear weaned orphaned or abandoned juveniles.

Communication

A. Vocal Communication.
1. Gorillas produce more than 15 recognized vocalizations. Some sounds are used mainly for group communication because gorillas are nearly invisible to each other while feeding and traveling in the vegetation. Deep belches are common during feeding and suggest contentment. Primate researcher Dian Fossey, trained observers in the field to mimic this sound when approaching feeding bands. Piglike grunts are used to establish right-of-way during foraging and to settle squabbles.
2. Male gorillas roar and growl during aggressive behaviors (Dixson, 1981). Silverbacks vocalize the most.
3. Infants whine, cry, and chuckle.
B. Visual communication.
1. The ritualized charge display is unique to gorillas and includes demonstrative body language. The entire sequence has nine steps: (1) hooting slow to fast, (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 (Hoff and Maple, 1982).
2. Other aggressive behaviors are stares, head jerks, lunges, grabbing, and biting.
3. Facial expressions for communicating include a play face, lip-tucking (tension), protruding tongue (uncertainty or concentration), and yawning (stress) (Dixson, 1981; Hoff and Maple, 1982).

Longevity

Gorillas live about 35 years in the wild and more than 50 years in a zoological environment. The mortality rate for immature gorillas under six years of age is over 40% and the risks are highest during the first year. Fighting silverbacks, predation, injury, and disease are all serious threats to youngsters that lessen as the apes reach maturity. However, the risks continue throughout life (Nowak, 1991).

Gorillas Height Weight Female 4.6 ft (1.4 m) 200 lb (90 kg) Male 5.6 ft (1.7 m) 400 lb (180 kg)

Here are some pictures of Gorilas