Source of Photograph.....

www.yesnet.yk.ca/.../alis_gorilla_project.htm

Biology
Classification and Range

Carl Linnaeus devised the classification system in zoology that we use today. In this system, humans and the three categories of great apes (chimpanzees, orangutans, and gorillas) all belong to the order Primates. Gorillas, the largest of the great apes, are divided into three subspecies: (1) western lowland gorillas (Gorillas gorilla gorilla), (2) eastern lowland gorillas (Gorilla gorilla graueri), and (3) mountain gorillas (Gorilla gorilla beringei). The three gorilla subspecies are very similar and show only minor differences in size, build, and coloring. The approximate ranges where each of the subspecies lives are shown on the map of Central Africa.

The eastern and western groups of gorillas are widely separated in location, but so similar in form that they must have come from a single parent population in the not too distant past. Since gorillas will not cross large rivers, such as the Zaire and Ubangi, the eminent gorilla specialist George Schaller suggested that the parent population probably lived in the area shown on the map. Today, most of this hypothetical range is too dry and open to be a suitable gorilla habitat, but during cooler and rainier conditions that existed 5000-7000 years ago, the area would have been covered by a rainforest where the gorillas could have lived.

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Population

The world's gorilla population is relatively small and still declining. All three gorilla subspecies are listed as endangered by the U.S. Fish and Wildlife Service and by the Convention on International Trade for Endangered Species. There are currently about 50,000 western lowland gorillas living in the wild in West Central Africa. This gorilla is also the type most often seen in zoos. The eastern lowland gorilla population has declined significantly in recent decades. An estimated 5,000-15,000 lived in the eastern Congolese rainforest around 1960. Today only about 2,500 remain in the wild, and only a few dozen live in the world's zoos. The mountain gorillas are the rarest of all and are on the verge of extinction. Only about 600 of these magnificent animals are left in the wild, about 320 in the Virunga Mountains and another 300 in the Bwindi Impenetrable Forest National Park in Uganda. None are found in captivity.

The population of mountain gorillas in the Virunga Mountains has been watched closely for the last half-century and shows the effects of human interaction, both good and bad. George Schaller estimated that about 450 mountain gorillas lived in the Virungas in 1960. Hunting and poaching reduced their numbers to about 250 by 1981, when the protection efforts of the late Dian Fossey and others brought the decline to a halt. Today about 320 mountain gorillas inhabit the Virungas, but their long-term survival continues to be threatened by natural changes and disasters, hunters and poachers, and the chronic political instability that swirls around the edge of their forest home.

Life Cycle of the Mountain Gorillas Newborn gorillas are small, covered with black hair, and weigh about 2.3 kg (5 lbs). They must be cared for at all times. By age two they are able to reach and chew on vines and branches. They develop about twice as fast as human babies.

Young male and female gorillas are classed as juvenile between the ages of about three and six. During this stage, both sexes have thick black hair and black skin. Juveniles of both sexes increase in size and weight at similar rates for the first six years. At age six they are about 1.2 m (4 ft) tall and weigh about 68 kg (150 lbs). Photo: Courtesy of the Dian Fossey Gorilla Fund

Females mature at about age six and cease to grow taller, although they continue to gain weight slowly until they reach weights of 113-136 kg (250-300 lbs) at ages of ten to eleven years. Males continue to grow both in size and weight past the age of six; they do not reach maturity until they are about ten years old. Between the ages of about six and ten years, males retain the uniformly black hair color of their youth and are called blackbacks.

When male mountain gorillas reach maturity, they develop a patch of grayish or silver-colored hair on their backs. Consequently, mature males are called silverbacks. Males cease to grow in size or weight after maturity, but at typical heights of 1.5-1.8 m (5-6 ft) and weights of 204-227 kg (450-500 lbs), they are impressively large animals. The silverbacks' large size and distinctive coloring make them very easy to recognize in the wild. Photo: Courtesy of the Dian Fossey Gorilla Fund

The maximum life span of mountain gorillas in the wild is difficult to estimate. The longest-lived gorillas in captivity reached ages of thirty to thirty-five years. No gorilla has been seen in the wild that looked as aged as the oldest captive gorillas, so the life span in the wild is probably somewhat less, perhaps twenty-five to thirty years.

The potential for population growth for undisturbed mountain gorillas is comparable to that for human beings. The gestation period is about nine months. Gorilla mothers with an infant may not have another for up to four years. There is also no apparent breeding season, since births of baby gorillas occur throughout the year. However, due to mishaps and disease, many baby gorillas die in the first year of life, and nearly half of all gorillas die before reaching adulthood. Photo: Courtesy of the Dian Fossey Gorilla Fund

Social Behavior

Lorna Anness, a Karisoke researcher, note taking in the rain wrote, "How close they get surprised me--I was shocked. And their tolerance--a mother would allow an infant to come right up and touch you."

Relationships within the [gorilla] group are very important. For instance, one day Puck, an adult female, and her son Cantsbee, a young blackback, were settling in to look for nest sites when it started to rain. Puck sat next to Intwali her two-year-old daughter, and Simba in a good position well out of the downpour. Cantsbee came along, staring at Simba, and moving closer and closer. Simba gave a slow pig-grunt at Cantsbee, but then Puck pig-grunted at Simba, while Cantsbee sidled even closer. Simba and Puck continued pig-grunting while Cantsbee slowly but surely pushed Simba out of the nest. He probably never would have tried to displace her if he had not known that Puck would back him up Schaller, 1989.

If this were the best of worlds, the sheer natural beauty of the animal would have sufficed as argument. But the Africans didn't even know whether they were beautiful or impressive--they'd never seen them [the gorillas]. When we did surveys in the 1970s, more than half the local population could not provide a single adjective of description. They lived in the shadow of these volcanoes and had no idea what the gorillas were like. So, they would flock to the films we showed, up to 3,000 people at a time from a village area, and the response was incredible. They saw how human this animal was. They saw a family unit; they saw a lot of maternal care--nursing, cleaning, playing, feeding; they saw paternal affection. These films did not show King Kong bursting through the bushes. Bill Weber, Assistant Director of Conservation, The New York Zoological Society.

Family Groups

Primates, in general, are very social animals, and mountain gorillas are no exception. They live in small family groups consisting of varying numbers of males, females, infants, and juveniles. Each group is led by a dominant male gorilla. The dominant silverback protects his group and leads in the search for food. In most monkey populations, the females stay with their family, while the males leave their groups at adolescence. In effect, mothers, daughters, sisters, and grandmothers stay together in family groups. A different social structure emerges among gorillas--females leave their family and join other groups. Above left: This family group reached a membership of thirty-five, including four silverbacks. Photo: Courtesy of the Dian Fossey Gorilla Fund

Since gorillas are highly social animals, they try to defend one another when danger threatens. For example, poachers trying to get a baby gorilla often have to kill the dominant silverback and mother first. The death of one animal also has an effect on many others. In particular, when the dominant silverback of a family group dies or is killed by disease, accident, or poachers, the family group may be severely disrupted. The large family group may split into two or more smaller groups. When a new silverback takes control of a family group, he may kill all of the infants of the dead silverback. This practice of infanticide is seen in various monkeys, prairie dogs, and lions (to name a few animals). It is an effective reproductive strategy in that the new male conceives progeny that perpetuate his genes. In stable peaceful groups, there is no apparent evidence of infanticide. Photo: Courtesy of the Dian Fossey Gorilla Fund

Gorillas' Communication

Gorillas are active in communicating with each other by both sounds and body language. Many of their actions reflect the hierarchy or pecking order of the group. Here a silverback makes a "threat gesture" by turning sideways to show his size and "yawning" to exhibit his large canine teeth.

Gorillas are known to make over twenty-five distinct sounds. Some of these areas follows:

• Hooting, vegetation slapping, and chest-beating, often accompanied by strutting. This is done by rival males.

• Sharp grunting: a sign of disapproval.

• Chuckling: a sign of playfulness.

• Screaming: a sign of alarm or warning.

• High-pitched barking: a sign of curiosity.

• Roaring: a sign of aggression.

• Belching: a sign of contentment.

Gorillas also love to play. Here, two gorillas play their favorite game, 'gotcha'! Photos: Courtesy of the Dian Fossey Gorilla Fund

Habitat and Diet
The image to the left is a mosaic of two SIR-C images obtained by Shuttle astronauts in 1994 is presented. The original images were processed and colored (slightly differently) by Dr. Scott Madry at the Rutgers Center for Remote Sensing and Spatial Analysis. Scene is about 68 km across. North is to upper left.

Habitat The image above shows the Virunga volcano chain, home to about half of the mountain gorillas remaining in the world. The pristine rainforest, shown in different shades of green in this false color image, appears as an irregular strip spanning the eight volcanoes of the chain. The forest is a small island of habitability for the gorillas surrounded by a vast sea of cleared agricultural lands, shown in light purple speckled with light green. The six volcanoes at the center and right end of the chain are dormant. The two at the left end are still very much alive, as indicated by the numerous distinct lava flows (in brown and purple) radiating from them.

There is a great span of elevation in the Virunga Mountain habitat of the mountain gorillas, ranging from about 1,525 m (5,000 ft) on the plains at the base of the volcanoes to over 3,965 m (13,000 ft) at the summits. The change in temperature and rainfall with elevation gives rise to a correspondingly wide range of forest and vegetation types. The distribution of the different vegetation types in the rainforest around the six dormant volcanoes is shown in this map developed by the Rutgers Gorilla Project.

The dominant types of land cover are the Hagenia forest, the bamboo forest, and the mixed Hagenia-bamboo forest. There are several other types occupying small areas, such as various types of grassy meadows, mimulopsis meadows, and alpine and subalpine growths dominated by the giant senecio plants. Similar vegetation types and zonations are found on the two active volcanoes off the left edge of the map, though the forests are a little drier and divided by abundant flows of frozen lava. Left: Typical Hagenia forest with dense brush near the ground and an open canopy of trees overhead. This scene is between Mounts Karisimbi and Visoke. Photo: Courtesy of the Dian Fossey Gorilla Fund

Based on observations by George Schaller and others, the Virunga mountain gorillas live within the area shown on the vegetation map. Most of them live on the slopes of the three dormant volcanoes in the lower portion of the map (Karisimbi, Mikeno, and Visoke); the rest live around the three dormant volcanoes in the upper portion (Sabinyo, Mgahinga, and Muhavura). No gorillas live around the two active volcanoes (Nyamlagira and Nyiragongo). Even within the area shown on the vegetation map, the gorillas apparently never climb above about 3,965 m (13,000 ft) and are seldom seen in the low area between the two groups of dormant volcanoes. Interestingly, the gorillas also seem to avoid open meadow areas, even preferring to go around a meadow rather than cross it. The gorillas are found most frequently in the Hagenia forests, seasonally in the bamboo forests, and occasionally in the subalpine vegetation zone. Why? The most basic reason of all--food!

Diet Mountain gorillas are primarily vegetarians. They eat many types of plants, including the roots and stems of some plants, the leaves and flowers of other plants, and even the bark of certain trees. Right: Gorilla eating inner bark of Hagenia tree. Photo: Courtesy of the Dian Fossey Gorilla Fund

They also eat the fruit of several types of trees and vines, wild celery, thistles, the tender shoots of bamboo plants, and certain vines in their entirety.

Most of the foods gorillas eat are found year-round in the Hagenia forests--so that is where they spend most of their time. It is their primary habitat. Bamboo shoots are available only a few months of the year, usually, but not always, between August and December. The gorillas visit the bamboo forests only when fresh shoots are available. Since the growth of bamboo shoots is highly variable from year to year, depending on weather, the bamboo forest is a secondary habitat for the gorillas. The gorillas also eat the soft centers of the giant senecio trees, so occasionally they make the long hike up the mountain sides to the subalpine zone where these plants live. The other vegetation zones have little for the gorillas to eat, so they are seldom, if ever, found there. Left: This gorilla is resting amid some gallium vines, a local fast-food favorite. They eat the whole thing: leaves, stems, flowers, and berries--the works! Gorillas often take naps after eating a meal in the middle of the day. Photo: Courtesy of the Dian Fossey Gorilla Fund

For the most part, the gorillas live peacefully within the confines of the mountain forests and avoid the open, cultivated fields of the surrounding humans. Occasionally, however, mountain gorillas have been known to enter the farmers' groves to forage for bananas!

Glossary

Acquired Immune Deficiency Syndrome Virus

A viral disease spread by contact of bodily fluids. The virus attacks the immune system and leaves the infected person susceptible to other diseases.

annual per capita income The average income earned per person in one year.

blackbacks A male mountain gorilla between the ages of six and ten that still has uniformly black hair coloring.

Dian Fossey Gorilla researcher who wrote the book Gorillas in the Mist.

ecotourism Tourism that provides revenues for biological conservation or community development.

GDP Gross domestic product. The gross national product excluding payments on foreign investments.

GIS Geographical information system. A collection of different digitized data sets that are related to the same geographic location.

Gorilla gorilla beringei A gorilla subspecies. This is the scientific name (genus and species) of the mountain gorillas.

GNP Gross national product. The total value of products or services produced by a country.

Idi Amin Dada Former dictator of Uganda (from 1971 to 1979).

population density The number of people in a given area. It is usually expressed as people per square kilometer. For example, suppose 100,000 people live in an area that is a rectangle of 10 km by 50 km. The area of the rectangle is 10 times 50, or 500 km2. The population density is 100,000 divided by 500, or 200 people per square kilometers.

pyrethrun A natural insecticide. This is one of the cash crops grown in Rwanda.

silverback A mature male mountain gorilla that has a patch of gray- or silver-colored hair on its back.

watershed An area of drainage that feeds into a stream system. For example, the Wheeling Creek watershed is the land area whose water can drain into Wheeling Creek (see the Water Quality module).

http://www.cotf.edu/ete/modules/mgorilla/mgbiology.html