Learning About Gorillas

Mountain gorillasGorillas are one of the four species of great apes that are the closest living relations of humans. The other three species are chimpanzees, bonobos and orangutans. All great apes have arms that are longer than their legs. Great apes are not considered monkeys because they are larger, walk upright for a longer period of time, don't have tails and have much larger, more developed brains than monkeys.

It was about nine million years ago that the genus Gorilla split from humans and chimps. About three million years after that the lineages of chimps and humans diverged.

Today there are two species of gorillas, each containing two subspecies. The appearances of each of the species are slightly different.

1. Eastern gorillas

They include two subspecies:

   Mountain gorilla (Gorilla beringei beringei). There are about 880 mountain gorillas, divided into two separate populations. The first population lives in the mountain forest of the Virunga volcanoes, which is shared between three countries: Rwanda, Uganda and the Democratic Republic of Congo. The second population lives in the Bwindi Impenetrable Forest, in Uganda.  Dian Fossey pioneered gorilla research with the mountain gorillas of the Virungas starting in 1967 when she established the Karisoke™ Research Center. Her work is still carried on today by the Dian Fossey Gorilla Fund International.

   A Grauer's gorillaGrauer's (Gorilla beringei graueri). Previously known as the eastern lowland gorilla. Most Grauer's gorillas live at heights in between mountainous and lowland forests, in a vast territory in the eastern Democratic Republic of Congo. Their name comes from Rudolf Grauer, the first Western scientist to identify this subspecies. In comparison to mountain gorillas, we know very little about the Grauer’s gorillas. Scientists do not even have a good estimate of the number of Grauer’s gorillas left, though it is agreed that their numbers have been greatly reduced in recent decades by habitat loss, poaching and armed conflict. The population is currently estimated at 5,000 individuals or perhaps fewer. The Dian Fossey Gorilla Fund has begun a new initiative to apply the Karisoke™ Research Center's successful model of daily monitoring and research  to six groups of Grauer's gorillas.


Eastern and mountain gorillas tend to have a more blackish coat than western gorillas. Mountain gorillas also have longer and thicker hair, which is adapted to their colder mountainous habitat. Grauer’s gorillas are the largest of the four subspecies.


2. Western gorillas

Found in west and central Africa, they include two sub-species.

   Western lowland gorilla, which is the species commonly found in zoos. Recent studies show that there are about 150,000 to 200,000 left in the wild. They are found in five African countries: Central African Republic, Republic of Congo, Cameroon, Gabon and Equatorial Guinea.

   Cross River gorilla, which number fewer than 300. They live in a fragmented forest located in Cameroon and Nigeria.

Typically, the western species tend to be brownish gray in color and have short, fine hair.


Because of the extensive research begun by Dr. Dian Fossey and continued by the Dian Fossey Gorilla Fund International, the mountain gorilla is perhaps the best understood of all wild gorilla populations.

Karisoke™ field trackersThe Fossey Fund closely monitors ten groups of mountain gorillas in Rwanda's Volcanoes National Park Parc. Staff at the Karisoke™ Research Center visit the mountain gorilla groups daily and report on their activities, and conduct anti-poaching patrols. Other gorilla groups designated for eco-tourism are also regularly monitored by the Rwanda Development Board.

Where do mountain gorillas live?


Mt. KarisimbiThe mountain gorillas studied by the Dian Fossey Gorilla Fund live in the Virunga Volcano Mountains, some of which reach as high as about 4,000 meters (more than 13,000 feet). The forests where the mountain gorillas live are often cloudy, misty and cold. At the bottom of the mountains the vegetation is very dense, becoming less so as you go higher up. Some of the common mammals that live in the forest with the mountain gorillas are: duikers, antelopes, hyraxes (a small furry animal related to the elephant), golden monkeys, and forest buffalo.

What is mountain gorilla family life like?

Typically, mountain gorillas live in groups that contain one or more adult males (ages 12 years or older, called silverbacks), several younger males (called blackbacks), adult females, juveniles and infants. The largest group recorded by the Dian Fossey Gorilla Fund is Pablo’s group, which reached 65 members at its largest.

A gorilla group restingThe dominant silverback gorilla (so named for the gleaming silver saddle of hair on his back) is in charge of the group's daily travels in search of food. He is also the center of attention during rest sessions and mediates conflicts within the group. In multi-silverback groups only one is dominant while the others support him, protecting the group from outside dangers such as intruding silverbacks from other groups, solitary males challenging the groups, and human threats such as poachers and traps set by illegal hunters.

The dominant silverback forms special bonds with the adult females in the group and fathers most of the offspring. Mother and infantMountain gorilla females can begin motherhood around age 10. The gestation period lasts about 8 and 1/2 months. Mother gorillas share a very close relationship with their infants for about four years, after which another sibling may be born. Mother gorillas hold newborns close to their chest at first, but soon the infant learns how to hold on for itself. Then it learns how to ride on the mother's back, until it is old enough to travel on its own. Their lifespan is 30 to 40 years.

How big do mountain gorillas get?

Silverback CantsbeeAdult male gorillas can reach 400 pounds (180-200 kg), and females can reach about 200 pounds (90 kg). Female gorillas don't have a crest on the top of their heads like the males, and have no silver on their backs. When a silverback gorilla is standing upright (say, during a chest beating display), they can be as tall as 5 and 1/2 feet (1.7 meters). A newborn gorilla weighs only about 4 and1/2 pounds (2kg)!

What do mountain gorillas eat?

A gorilla treatThe mountain gorilla diet is mostly plants like celery, nettles, bamboo and thistles, and they are quite particular about which parts of each plant they like to eat. Sometimes they also find ant nests and eat the ants, along with an occasional worm or grub. There isn't much fruit where mountain gorillas live, but they do love to eat the wild berries that grow in their habitat. The mountain gorillas spend a lot of their time traveling in search of food. Their food is normally evenly distributed in their habitat and abundantly available throughout the year. Only a few mountain gorilla foods are seasonal, such as bamboo shoots, which are one of the gorillas' favorite delicacies. The full-grown mountain gorilla diet can include up to 60 pounds (25 kg) of vegetation a day!

How do mountain gorillas communicate?

Sending a messageEveryone who works with the mountain gorillas agrees that they are generally peaceful and gentle. The gorillas that are observed by the Fossey Fund, as well as the groups that are visited by tourists, have been habituated to the presence of humans. But this doesn't mean that the gorillas won't sometimes charge, scream or bare their teeth, whether at an outsider or within the group itself. Most of these actions are just meant to serve as warnings, to ward off danger or to prevent a fight.

Mountain gorillas can communicate in a variety of ways, including facial expressions, sounds, postures and gestures. One of the nicest sounds is heard when the group is resting after a period of feeding. This sound is something like a soft purring and is called a "belch vocalization." When the gorillas feel threatened, they can make a variety of loud sounds, like roars or screams. Facial expressions are also used for communication. For example, an open mouth with both upper and lower teeth showing means aggressions. But a closed mouth with clenched teeth may signal anger as well.

And, of course, there's the classic chest beating by male gorillas, which is used to show stature, scare off opponents or even to prevent a fight.


Most of the time mountain gorillas travel on the ground on all fours. They will distribute their weight on their knuckles as opposed to their palms, which is why it is called “knuckle walking.” Sometimes gorillas walk bipedally, but rarely go further than three meters on two feet.

Night nests

Gorillas use vines, leaves and branches to fashion a rim around themselves and to pad the ground underneath them. They build fresh nests every evening in a different place depending on their daily travels. Each gorilla builds its own nest, but infants share their mother's night nests. Nest counting is an accurate method used during censuses to estimate the number of gorillas.


How does the Dian Fossey Gorilla Fund monitor gorillas?


Monitoring the gorillas every dayEach morning, trackers locate their assigned gorilla group by going to their night nest locations and then following the trail of crushed vegetation the gorillas left behind as they started moving.  After finding the group and recording its location via a global positioning system (GPS), the trackers will find each individual in the group and record information on its general appearance and health as well as any change in group composition due to births, deaths, immigration or emigration in order to track the population dynamic. In addition, national and international researchers collect detailed information on behavior for the Dian Fossey Gorilla Fund’s long-term gorilla research database and specific studies. 

Gorillas are identified by their "nose prints," which are the patterns of wrinkles on their noses. Each gorilla has a unique nose print. Karisoke™ researchers use photographs and illustrations of the gorillas’ noses in order to identify and monitor individual gorillas.


Because nose prints can change over the course of an individual's lifetime, the Dian Fossey Gorilla Fund updates the nose print file each year for each of the approximately 120 gorillas we monitor.

How do scientists study the gorillas?

Taking a urine sampleIn addition to the ongoing research about mountain gorilla life, scientists are now using some of the most up-to-date scientific methods to learn even more. For example, a study is currently underway using DNA samples taken from the gorillas' droppings, in order to learn the exact paternity for each new infant born in a gorilla group. Scientists are also attempting to classify all of the plants in the forests, upon which the gorillas and other species rely for food. Using a new process called hyperspectral remote sensing, they can collect information using aerial photographs, and then compare this information with other data collected on the gorillas and even the poaching activity in the area. The Geographical Information System (GIS) is also used to illustrate gorilla movements over time, as well as to record the location of illegal activities in order to design an efficient protection strategy.

Will the mountain gorilla survive?

The year 2002 marked the 100th year since the mountain gorilla was first scientifically identified as a distinct subspecies of gorilla. The future of the gorillas is most dependent on the protection and survival of the forests in which they live, since they depend on this land for food, safety and normal activities. But the forests are often in danger from growing human populations, and from civil war in the region. The mountain gorillas are classified as a critically endangered species, whose survival is strictly dependent on daily collaboration among conservation institutions working in the region.

Threats to gorilla survival


Caught in a snareAll types of gorillas in Africa are endangered, primarily due to human activity such as poaching, disease transmission, and habitat destruction. Ultimately, human poverty is the greatest threat to gorillas.  Gorillas live in countries in Africa with some of the highest population densities and lowest adult life spans, literacy rates, and standards of living in the world.  The challenges that such intense poverty brings to gorilla conservation vary depending on where in Africa the gorillas live.  Western gorillas, which inhabit five west African countries from Nigeria to the Republic of Congo, are primarily threatened by illegal hunting for food, habitat loss from logging, and disease — specifically the Ebola virus, which has a roughly 95% mortality rate in gorillas.  Eastern gorillas are found only in Rwanda, Uganda and the Democratic Republic of Congo, and are not generally hunted for food like their western counterparts. They are primarily threatened by habitat loss when their forests are converted to farmland and pasture; local civil unrest; poachers’ snares set for other animals such as antelope; respiratory and other diseases probably transmitted by humans; and poaching for the gorilla infant trade.

What is my future?The only type of gorilla that is known to be increasing is the mountain gorilla. Between 1989 and 2003, the Virunga mountain gorilla population increased by 17 percent, and nearly all that increase occurred within the sector of the park that is protected by the Fossey Fund. This is astounding, particularly given that civil wars occurred in both Rwanda and Congo during portions of that time period. By the next census, in 2010, the population had again increased, by 26.3 percent, with almost a quarter of the increase occurring in the Fossey Fund sector. These increases are attributed to the intense conservation efforts of the national park authorities of Rwanda, Congo and Uganda as well as the Dian Fossey Gorilla Fund International and its partners.

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