Pace - Mountain Gorillas by Tusk Trust

Mountain Gorillas

PACE – Pan African Conservation Education was created by Tusk and Siren Conservation Education in 2004.

This booklet on mountain gorillas was requested by people in Bwindi Uganda. It was created by Penny Fraser, PACE Coordinator with Richard Bagyeni and his colleagues at Conservation Through Public Health. Their knowledge, experience and wonderful photographs made this publication what it is.

Design and layout by Katie Puremont.

We appreciate Jo-Anne McArthur / We Animals allowing us to use her beautiful photo of a blackback mountain gorilla on the front cover.

Published by Tusk Trust, 4 Cheapside House, Gillingham, Dorset SP8 4AA, UK

First published 2024.

A catalogue record for this booklet is available from the British Library.

ISBN 9781916340176

Moral rights of the authors have been asserted. All rights reserved. The authors have made every effort to ensure the accuracy and currency of the information in this publication. The authors disclaim any liability for loss, injury or damage incurred as a consequence, directly or indirectly, from the use and application of the contents of this booklet.

PACE – Pan African Conservation Education

PACE is an education programme of Tusk. PACE is about helping people solve their everyday environmental problems, especially problems that impact on their wellbeing, and on the wildlife and ecosystems we all depend on. PACE works with conservation and education partners across Africa. We strive to connect people with nature, to understand, value and protect it.

Our educational resources are available free of charge. They are arranged in modules: Living with Wildlife, Water, Soil, Trees, Energy, Living by the Ocean, Urban Living, Health and Careers in Conservation. This resource on mountain gorillas is part of the Living with Wildlife module.

Why mountain gorillas?

Mountain gorillas are the largest of the great apes – they are big, intelligent, caring and charismatic creatures that live in just two areas of mountains that span the borders of Uganda, Democratic Republic of Congo (DRC) and Rwanda. Mountain gorillas are one of the world’s great conservation successes. Nearly extinct in the 1970s, thanks to commitment from local communities and national governments, their numbers have nearly doubled. In 2023 there were one thousand and sixty three. They are still classified as endangered, but their future now looks brighter and the species is thriving. They are a global tourist attraction – in Uganda mountain gorillas generate up to $25 million a year from tourism revenue. This helps the country, and it helps people living close to the national parks through the good roads, schools, health care and employment that their gorillas have brought them.

Read on, to learn more about these amazing animals – one of our closest relatives!

Conservation Through Public Health is a Ugandan organisation set up in 2003. Its work with mountain gorillas and the communities living close to them in and around the Bwindi National Park in Uganda has been hugely succesful – livelihoods have improved and the mountain gorillas are thriving! This resource was requested by people in Bwindi, for their own children to learn, and to showcase their flagship species to others!

We share 98% of our genes with gorillas. That means that we are 98% the same as gorillas!

Mountain gorillas

Gorilla beringei beringei

Taxonomy

Gorillas are primates, just like us human beings. Like us they are in the family Hominoidae.

Class – Mammal

Order – Primate

Family – Hominoidae

Genus – Gorilla

There are two species of gorilla, eastern and western. They each have two sub-species.

The eastern gorillas – Gorilla beringei – live in DRC, Uganda and Rwanda.

The mountain gorillas Gorilla beringei beringei, are in the mountains.

Their lowland cousins Gorilla beringei graueri are different and they live in lowland rainforest, just in DRC.

The family Hominoidae includes great apes, and lesser apes.

The great apes are:

Humans – Homo sapiens

Chimpanzee – Pan troglodytes

Bonobo – Pan paniscus

Gorilla – Gorilla beringei and Gorilla gorilla Orangutan – Pongo pygmaeus, Pongo Abelii & Pongo tapanuliensis.

Gorillas are the largest of all the great apes.

Primatologist is a person who studies primates.

Description / Appearance

Mountain gorillas have thick black fur. They are the size of an average human, but bulkier, with strong muscular bodies, large heads, long arms, and strong hands.

Adult males are 1.4-1.8m tall, and weigh 200-230 kg, sometimes 350kg. Females are smaller, 1.2-1.5m tall, 65-115kg.

With both arms outstretched, a silverback can be 2.6m from one finger tip to the other!

They have brown eyes, and big tummies.

Mountain gorillas are very intelligent. They are curious, caring, have strong emotional bonds and good memory. They are very social animals.

Their hands and feet are very much like our own. Each mountain gorilla has its own personality and character.

Life span

Mountain gorillas can live to 55 years old.

Gorillas are the largest of all the great apes.

Family

Mountain gorillas usually live in family groups. Ten individuals is typical – an adult male, up to five females and their offspring. It can be just two or three, or up to 35.

Some groups have more males. Mixed sex groups are always led by one dominant silverback.

Some groups will all be related by birth. In others they all have different family background, or lineage.

One group of 65 gorillas has been known.

Adult females

A female mountain gorilla matures at 8-10 years old.

There is a ‘pecking order’ amongst the females. The first to join the group is the senior, or highest ranked.

Females compete to groom the silverback, all trying to be his favourite.

Mountain gorilla family group in a forest clearing

Mountain gorillas have strong family bonds.

Infants

Mountain gorillas are called infants from birth until 3-4 years old. For the first 5-6 months they are carried by their mama as they are very vulnerable and dependent on her. At 1½ years they start to move a bit further from the mother.

Mothers carry very young babies close against their chest. Then after 4-5 months encourage them to cling onto her back instead.

Juveniles

Mountain gorillas between 4 and 7 years old are called juveniles.

Juveniles need to eat less than adults, this means they can spend lots of time playing and exploring. They like chasing each other, tumbling, wrestling, tickling, and climbing on each other and their family members. They like climbing on trees and bushes.

The adults make sure they don’t wander too far. They are patient and affectionate with the youngsters, guiding and disciplining with stern looks, a grunt or irritated posture.

Infant on its mama’s back in the Mubare group in Bwindi Mama and infant, Bwindi in Uganda

Blackbacks or young males

Sexually immature males are blackbacks. They are subordinate to the silverback, and will help him if the family is threatened.

When blackbacks mature, at 10-13 years old, they usually leave their family group and join other young adults.

Silverback

When male gorillas become sexually mature, at 10-13 years, they grow silver hair on their backs. They grow large canine teeth and a sagittal crest. Sagittal crest is a stronger bone down the middle of the skull that makes the head look higher and bigger.

A silverback is able to become the leader of a family group. Young silverbacks usually leave their birth family, to live in a group with other young males, or to find females and form their own family.

The silverback protects the family. He often sits alone, watching and listening for signs of danger. He keeps track of everyone, to ensure

they are safe and don’t stray away from the group.

Silverbacks make decisions about where and when to feed, rest and sleep. They decide the speed and route the family will use.

When he gets old, or weak, his females sometimes leave for a stronger male. Younger silverbacks may challenge him, wanting to take his place as leader. Sometimes they fight to death, or the loser retreats to live alone in the forest. One in Bwindi called Ruhondeza actually went to live near a village on the forest edge. He felt safer close to people and their farms than in the forest.

Blackback brothers relax in their nests in the Kwitonda group in Volcanoes National Park, Rwanda

Maraya, the lead silverback of the Mubare family in Bwindi

Distribution

Mountain gorillas live in only two places in the world, Bwindi Impenetrable Forest National Park in Uganda, and The Virunga Volcanoes that span the border of DRC, Rwanda and Uganda.

The two populations are separate, there is a large distance of farmed land between them, so they do not meet.

Range size

The range – the area where individuals or each group live varies from 3-24 km2. Each gorilla group has its own area, they don’t usually overlap.

Population

In 2018 there were 1084 mountain gorillas: 459 in Bwindi.

A census, is a count or estimate of a population. A census is usually done every five years. The census surveys are time consuming because forest is dense and steep, and the area large. Groups of researchers and rangers walk through the whole area, working at the same time, covering different sections. They move in lines, side by side, recording gorillas they see and evidence of gorillas: tracks, trails of broken vegetation, nests, faeces. Faeces is collected and tested for DNA. Most gorillas leave poop in their nest. Each of them has different DNA, so testing the poop for DNA tells us how many different gorillas have been in the area.

Mountain gorillas only live in Africa, in these two areas.

Mountain gorillas only live in the wild. There are none in zoos –anywhere in the world.

Rangers collecting fecal samples

Gorilla beringei beringei

Habitat

Mountain gorillas live in tropical montane rain forests (2700- 4500m altitude), where it is often very steep and inhospitable. The vegetation can be dense and difficult to move through. There are ravines and fast flowing rivers. It is often misty, and rains a lot. The climate can be chilly. The mountain gorillas have thick black fur to protect them from the cold, wet climate.

Habitat means the kind of place where something lives.

Food / diet

Mountain gorillas have a varied diet, they mostly eat the leaves, stem, pith and bark of plants. They also like the roots of plants and enjoy fruits. Occasionally they eat ants, termites, snails, larvae and grubs.

They love plantains and bananas, especially the stems! Bamboo is also a favourite food. They may eat from more than 260 species of plant. They like wild celery, wild blackberries, thistles and mistletoe.

They have very big bellies and spend a lot of time eating, and just sitting around digesting.

Their food contains coarse roughage, or fibre, that takes a long time to digest.

Bwindi National Park

Mountain gorillas have extra long large intestine to digest all the coarse plants they eat.

They fart a lot!

They eat coffee berries, but don‘t like tea!

PACE Mountain Gorillas

Infant breast feeding, Rwanda

Mubare gorilla group feeding

Feeding on leaves and stem

Mountain gorillas belch a lot!

Reproduction

Male mountain gorillas become sexually mature at 10-12 years old, females at 8-10 years old.

Adult females usually live in family groups that are led by a silver back. Breeding silverbacks are polygamous, they will have a group or harem of up to five or six females. The silverback protects the family.

Females normally give birth to a single baby every 4-5 years. Twins are rare.

The silverback fathers all the babies in his family, though sometimes when he is not looking, the younger males sire a baby with a female not related to them.

Gestation is eight and a half months.

A newborn baby is very vulnerable and dependant on its mother. She carries the baby for the first 5 months of its life. She suckles her infant for 3-4 years, though it will start to eat leaves and other foods at 6-8 months old. When the infant is weaned, the mother can become pregnant again.

Movement

Mountain gorillas can climb, but they mostly live and move on the ground.

They do walk upright, on two legs, like we do, but most often walk on both hands and feet. They use the knuckles, not palms of their hands to walk on.

It is easy to follow mountain gorillas in the forest because they leave a clear trail of broken vegetation where they have passed by.

Routine

Wake up, Walk, Eat, Rest, Eat, Make a nest, Eat supper, Sleep. Wake up, walk, eat, rest, …

Gorilla groups don’t stay in one place for more than one night. They will move an average of 0.5 -1km a day as they forage, depending on food availability. However, they will move further, sometimes great distances, to reach a favourite food, like a tree in fruit, or particular plants.

Resting takes nearly half of the day. They like to sunbathe, They play, groom, nap, and cuddle, protected and supervised by their silverback. The group always stay close together.

They use undergrowth and trees to shelter when there is rain and bad weather.

Every night each mountain gorilla builds a nest from fresh plant material. Nests are made from weaving and folding materials together to make a comfortable place to sleep. They use branches and leaves of trees, and stems and leaves of herbaceous plants.

Nests are made close to other group members, on the ground or low branches of trees and bushes.

Sometimes they make day nests as well.

Infants will sleep with their mother in her nest until they are 3-4 years old.

Mountain gorillas relaxing in the Rwanda forest

A family resting, Bwindi, Uganda

Bwindi mountain gorilla family resting

Knuckle walking – walking on four limbs, supporting body weight on knuckles of hands, as well as the feet.

Mountain Gorillas

Mountain gorilla nest, Virunga Park in Rwanda

Folivore – an animal that eats mostly leaves.

Bi-pedal – means to walk upright on two feet.

Communication

Mountain gorillas communicate in many different ways – they use sounds, gestures, posture and behaviour.

A grunt, like a pig grunt, is used to discipline another gorilla.

A deep belch, purr, hum or moan usually expresses contentment.

Mountain gorillas chuckle when they are playing, and a short bark is used to ask ‘What is that?’ or ‘Who is that?’

Infants and juveniles cry or wail when separated from their mama – a cry can turn into a temper tantrum just like young children who are cross!

Wraagh! is an adult response to sudden stress, an unexpected human, loud wind or another species making an alarm call.

Screams – loud repeated screams are made mostly by silverbacks, but any age or sex when there is a dispute or threat.

A scream is an alarm call.

Silverbacks are gentle, caring, and nurturing to their family, but they are the protectors. They use intimidating behaviour, sounds and postures to scare and frighten people or animals they think are threatening themselves or their family.

Roar – the silverback roars when he is threatened or stressed. Roaring is an aggressive call. It is usually followed by charging and lunging at the threat.

He will bare his teeth, beat his chest, make mock-charges, strut, glare, and other bravado! The hair on a silverback’s head will stand up when he is displaying.

Hoot series – is repeated loud hoots, getting longer and louder. Hoot series can be heard far away. A silverback may use a hoot series to warn another family group that he is around.

Silverback posturing, Mgahinga National Park, Uganda

Grooming

Mountain gorillas groom each other for cleanliness and to bond and strengthen relationships. Females groom each other, and they compete to groom the silverback, trying to be his favourite. Mothers groom their offspring. Silverbacks rarely groom others, because they are the boss!

Predators

Mountain gorillas don’t have many predators. Leopards may threaten weak gorillas, and humans hunted them in the past.

Other dangers

Fighting – most wounds mountain gorillas suffer are from fighting with other mountain gorillas! Humans and human activity are the biggest threat they face. But all in all our two species have learned to live alongside eachother peacefully.

Mountain gorilla conservation is a success story. We must keep it that way!

Blackbacks play fighting, Rwanda

Mountain gorilla tourism

Mountain gorillas are famous across the world. People travel from far and wide, paying a lot of money to experience them up close in the wild. In Uganda alone, mountain gorilla tourism earns $25 million a year! The tourism provides jobs, and has paid for new hospitals, schools and roads for people close to the national parks. Tourism supports local businesses, provides income for government, and educational scholarships, healthcare and community development for communities living alongside the gorillas.

When scientists started studying wild mountain gorillas in the 1960s, they found that they habituate to people, in a way that lowland gorillas do not.

Habituate means get used to.

It takes two years to habituate a mountain gorilla group. Rangers will gradually, slowly, calmly and respectfully get closer, until the gorillas are happy to have people near to them.

Wildlife rangers have habituated certain mountain gorilla groups for tourism. Twelve groups in Bwindi have paying tourists visit them. Up to eight people, with rangers, guides, porters and guards can visit each group for 1 hour each day. They can not get closer than 10m. The gorillas are wild and free. Rangers know generally where there are in the forest, but the tourist groups may have to walk for hours tracking them.

Living together – people and mountain gorillas

Mountain gorillas are naturally shy of people. But the edge of the forest is next to farmland and they are curious and they like some crops, so occasionally enter farms.

They sometimes even walk along roads at the forest edge.

Habituation and tourism can cause stress for mountain gorillas.

Mountain gorillas eat coffee berries, but don’t like tea. They usually don’t enter a field of tea. Growing tea discourages, but doesn’t prevent mountain gorillas from visiting. They love bananas, especially the pith, so growing bananas or plantains is an invitation for mountain gorillas to visit!

Local people are not afraid if they see gorillas because they know what to do and not to do, and who to call. Villages have Human and Gorilla Conflict Resolution Teams (HUGOs). HUGOs are volunteers, always available, and trained to herd gorillas back into the National Park safely and firmly, without frightening or angering gorillas or people.

In 2020 there was a mountain gorilla baby boom.

Health

All mountain gorillas suffer cuts, wounds and other injuries from life in the forest. But most of their wounds are actually from fighting. Silverbacks fight with each other, to defend their family, or to seize females or even a whole group from a rival.

Mountain gorillas have herbal medicines, plants they use to treat infections and ailments. They also use plants to stay healthy and keep diseases away. They love to eat young eucalyptus leaves, and Afromonum, a kind of wild ginger. They like the bark of Prunus africana (Pygeum) trees. All these plants are also medicinal for us.

One Health

Because mountain gorillas are very similar to us, they suffer the same diseases and health problems as we do: common colds, tuberculosis (TB), pneumonia, cholera, typhoid, malaria, parasites like scabies, ticks and intestinal worms. They can pass germs to us, and we to them.

The health of the gorillas is monitored.

The health of people around the park, and their livestock, is also monitored. There are extra health care workers for this, many are volunteers, and there are extra facilities.

ZOONOSE - is a disease that passes from people to animals, or animals to people

Sixty percent – 60% – of all mountain gorilla are habituated to humans.

The local communities take care to keep parasites, infectious disease and germs under control. Sanitation and hygiene is very strong. This attention to public health keeps people safe, and it keeps the gorillas safe.

Noting a gorilla’s information before collecting faecal samples

A community nurse, Bwindi, Uganda

Stephen Rubanga, CTPH co-founder

& chief veterinary technician examining gorilla faecal samples in their lab.

References

Gladys Kalema-Zikusoka. 2023. Walking with Gorillas. Arcade Publishing. USA.

Dian Fossey. 1983. Gorillas in the Mist. Hodder and Stoughton. London.

Jessica Ganas, Sylvia Ortmann, Martha M. Robbins. 2008. Food preferences of wild Mountain Gorillas. American Journal of Primatology 70:927–938

Wisconsin National Primate Research Centre. https://primate.wisc.edu/primate-info-net/pinfactsheets/pin-factsheet-gorilla/

Counting elusive animals: Comparing field and genetic census of the entire mountain gorilla population of Bwindi Impenetrable National Park, Uganda. K. Guschanski, L. Vigilant, A. McNeilage, M. Gray, E. Kagoda, & M.M. Robbins. Biological Conservation.Vol. 142, Issue 2, February 2009, Pages 290-300

Population dynamics of the virunga gorillas: 1959–1978. A.W. Weber & A. Vedder. Biological Conservation. Vol. 26, Issue 4, 1983, Pages 341-366

Genetic census reveals increased but uneven growth of a critically endangered mountain gorilla population. M. Gray, J. Roy, L. Vigilant, K. Fawcett, A. Basabose, M. Cranfield, P. Uwingeli, I. Mburanumwe, E. Kagoda & M. Robbins. Biological Conservation. Vol. 158, February 2013, Pages 230-238

Estimating abundance and growth rates in a wild mountain gorilla population. A.-C. Granjon, M. M. Robbins, J. Arinaitwe, M. R. Cranfield, W. Eckardt, I. Mburanumwe, A. Musana, A. M. Robbins, J. Roy, R. Sollmann, L. Vigilant, & J. R. Hickey. Animal Conservation. First published: 13 January 2020 https://doi.org/10.1111/acv.12559

Mountain Gorilla Population Growth.

https://www.berggorilla.org/en/gorillas/species/

CTPH The Gorilla guardians. Video. https://youtube/St05oNcYhPo

Picture credits

Graph on page 13 recreated from CTPH.

Page 13 photo; page 16 top photo, feeding on leaves and stems; page 16 bottom, silverback Maraya of Mubare group; page21 bottom photo, family resting in Bwindi; page26 bottom, juveniles grooming; page 29 top right, eating bananas, are all © CTPH.

Somebody somewhere has found a solution! The idea behind PACE is to spread simple solutions to environmental problems between communities across Africa, from fuel-saving stoves to rainwater harvesting, solving human-wildlife conflict, compost making to tree farming. PACE shares information about the environment and wildlife, and the very practical ways in which people are addressing common environmental problems so that we people, wildlife and our planet have a secure and healthy future. There are ten modules in the PACE pack, this booklet is part of the Living with Wildlife module.

PACE is for students, teachers, community use and general reading Contact pace@tusk.org www.paceproject.net

Acknowledgements

Tusk thanks DHL for their significant and generous support of PACE. Their support has been fundamental to our success to date.