Meet the Chimpanzees

The Wild Mahale Mountains
Text by Michio Nakamura
Photographs by Luca De Santis

Chimpanzee research at Mahale was started in 1965. The one who started the research there was Toshisada Nishida. He was, at the time, just a graduate student studying at Kyoto University, Japan. Since then, the research project has been continued seamlessly by many researchers for more than 50 years. It is not so common that a research project on a single mammalian species is continued at one place that long. From early on, the Japanese researchers had proposed to make Mahale as a protected area.

Thus it eventually became a national park of Tanzania in 1985 with efforts by Japanese researchers. The financial support was given from the Japan International Cooperation Agency and it is a rare example that a national park was established through overseas aid by a Japanese governmental organization.

The Mahale Mountains National Park is located on the eastern shore of the Lake Tanganyika at the western side of Tanzania covering the area of about 1,600 square kilometers. The Mahale Mountains chain runs from north-west to south-east with the highest peak, Mt. Nkungwe, being 2,462 m above sea level. This mountain chain keeps the moist from the lake and in the wet season it rains heavily on the western side of the mountains. The mountains gather the rain water which flows down to the lake as many small streams. As such, a rich forest, called the Kasoje Forest, is developed between the lake and the Mahale Mountains. This forest is the home for the M group chimpanzees that is the subject of ongoing research and tourism at Mahale. 

Mahale is also a home for various other animals. On trees of the Kasoje Forest, one would easily see small monkeys with clown-like gaily faces: the red-tailed monkeys. Red colobus monkeys, yellow baboons, several kinds of squirrels, warthogs, vervet monkeys, and the Nile monitor lizards can also be seen frequently near the research camp. 

On the rather dim observation trails, one would often see a blue duiker, a small antelope that stands motionless fluttering only its small tail. At a certain distance, it suddenly skirls and runs into bush. Leopards, porcupines, pangolins, aardvarks, bushpigs, and hyenas are also inhabitants of this forest and although you may not directly see them because of their nocturnal nature, you will find their feces on the observation trail. In the lake and river mouth, hippos, buffalos, and otters are also present. When darkness covers the entire forest, you will hear the loud voices of greater galagos. You will also hear insects, frogs, nightjars, as well as the sounds of footsteps of nocturnal animals wandering about. Magnificent to hear may be the deep bass roar of the leopard known as “sawing sound.” The night at Mahale is also a busy quarter for wildlife.

Introduction to the Chimpanzee

As it is well known, we humans belong to the order Primates (an order including lemurs, monkeys, and apes). Therefore, studying various species of primates is essential for understanding what we are and how we evolved. The chimpanzee is, among several hundreds of species of primates, the closest sister species to humans. Some scholars even argue that due to its genetic closeness to humans, the chimpanzee should be included in our own genus, Homo.

Chimpanzee males in the wild weigh around 35 to 50 kg (some are over 60 kg in zoos) and females are about 10% smaller. If they stand bipedal, they are as high as 130 cm, much smaller than an average human female. This is because they have much shorter hind legs than we do, but instead they have longer hands. Chimpanzees are much stouter-built than we are. Especially, chimpanzee males are muscular and much stronger than human males. They especially look large when they erect their body hair. This piloerection may have the same mechanism as our gooseflesh when we get excited or feel tense. The difference is that we have very poor body hairs so that only pores of skin are visible as gooseflesh when we erect our hair.


Important foods for chimpanzees are ripe wild fruits. However, they also eat other parts of plants such as leaves, piths, flowers, or resins. Mahale chimpanzees are known to utilize more than 400 items from more than 200 species of plants. This number is still increasing as research goes on.

Fruits usually have their seasons. That means chimpanzees’ important food habitat changes depending on seasons. What they eat are mostly “eatable” also to humans. Some fruits are good tasted and even sought for by local people. Some are too sour or too rough for humans but are sweet at the same time. 

Mahale chimpanzees also eat some agricultural species such as lemons, guavas, and mangoes that are once cultivated by the local people but abandoned after Mahale became a national park and now have gone wild. However, strangely, chimpanzees in Mahale never utilize oil palm fruits that are high in calorie and eaten quite frequently by chimpanzees in Gombe which is also in Tanzania. This difference is not due to availability because we often see fruiting oil palms in the Kasoje Forest.

When chimpanzees find ripe fruits in the forest, they may emit a grunting vocalization. The local assistants call this vocalization “a voice of delight.” Once an alpha male, Fanana, tended to emit this sound often while climbing a fruiting tree and his grunting sometimes even became a cry.

Chimpanzees’ lips stretch very well and they often put many fruits in between teeth and lips and compress the mass of fruits to squeeze juice. After squeezing, they spit out the leftover fiber ball, called a “wadge.” Many wild fruits are tightly adhered to their seeds and cannot easily be removed. In such a case, chimpanzees swallow the whole fruits together with the seeds. You will often see many seeds are included intact in their feces. Such seeds are known to germinate better than seeds naturally fallen on the ground because the surface of seeds are moderately softened while going through the gut of a chimpanzee. The seeds in the feces are also an important source to know the foods of chimpanzees in a particular season.

Plants are their main foods but chimpanzees are not vegetarians. They also eat social insects such as ants and they love mammal meat very much. Chimpanzees at Mahale use tool to “fish” for arboreal Camponotus ants. The major mammalian prey is the red colobus monkey. When they hunt colobus monkeys, they get very excited, and when succeeded, noisy uproar of “carnival” continues sometimes for hours.

Social Unit and Fission-Fusion

Many primate species such as most monkey species form a stable group, often called a “troop.” A troop is usually a compact group and you may visually confirm its members as they often are in close vicinity. On the other hand, in a chimpanzee social group, its members are not always physically together. It may depend on the season, but usually an observer will see only a few to a dozen of chimpanzees moving together at a time. Such small temporal group is called a “party” (or “subgroup”) whose size and composition are not constant and always subject to change. For example, a chimpanzee A may be observed walking alone, or together with B, C, and D, but later on, he may be observed with B and E, and so on. A chimpanzee will meet and part with any chimpanzees in a group.

With such a fluid characteristics, western researchers first thought that chimpanzees did not have a stable social group except for enduring mother and offspring pairs. They thought that chimpanzees had a loose “community” in which any chimpanzees might meet and part without any boundary.

However, from the early days, Japanese researchers thought that the chimpanzee has a distinctive social group with distinct boundary and stable membership. Nishida recorded the membership and composition of parties for months and found out that there was an upper limit for the membership. Thus, chimpanzees are not moving within borderless community but actually they do so within a social group that is distinctive from another group. Thus Nishida called this a “unit-group” of chimpanzees. A few years later, researchers at Mahale found out that neighboring unit-groups are usually hostile with each other but females transfer between these unit-groups upon reaching sexual maturity.

Nowadays, western researchers also admit that chimpanzees have a distinct social group (but they somehow continue to use the term “community” that sometimes brings some confusion). A chimpanzee unit-group has around 50 members on average, with the smallest around 10 to the largest over 150.


There is no specific breeding season or mating season in chimpanzees. Instead, a female has an estrous period and when she is in estrous, her rump is swelled large and pink. Sexual cycle is around 35 days within which the large sexual swelling continues for about 10 days and a female accepts males only during this swelling period. When she gives a birth, she will not show estrous swelling for 4 to 5 years while she is nursing the baby. Therefore, the number of sexually active females is not so many at one time. There are about 20 to 30 adult females in the Mahale M group but maybe only one to two, four or five at the most, females at a time show estrous and thus can accept males.

A male starts to mate with adult females when he is still an infant. When he is about to wean and his mother resumes estrous, he may mate also with his mother. In the human sense, it may seem immoral to mate with one’s own mother, but the mating actually does not seem “sexual” at all. It is rather a kind of mother–infant intercourse through physical touch. The mating by an infant male may be playful or may be a practice for sexual mating. The mother may present to her infant son to comfort him when he is in distress. When a male becomes old enough to be able to ejaculate, he usually do not mate with his mother or sister.

A typical mating between adults goes something as follows. A male may perform a courtship display to a female, and if she is willing, she will rush to the male and present her sexual swelling. But in some cases, a female performs a courtship display to a male or even presents him when he is not willing. There are various kinds of courtship displays that are known to differ between populations. When both participants are willing, male will mount the female, insert his penis and thrust several times. The intromission time is usually short. It is common that female emit a squeak voice and runs a few meters away from the male soon after copulation. The male may again approach the female and groom her for a while or otherwise they may part.


Chimpanzees develop very slowly. In infancy (0 to 4 years old), the baby suckles the mother’s milk and is usually carried by the mother either in the belly or on the back. When weaned, he/she enters juvenility (5 to 8 years old). Now the child can eat by his/her own and is no more carried by the mother, but still dependent on the mother in ranging. When a boy chimpanzee is playing with his friends, he may suddenly notice that his mother is not nearby. Then he will start to emit whimper call and desperately look for the mother. When he cannot find his mom, he may begin to scream.

By reaching sexual maturity, chimpanzees enter the adolescence (male: 9 to 15 years old; female: 9 to 12 years old). A male’s testes begin to hang down and now he can ejaculate. But an adolescent male is still much smaller than adult males. Females begin to show small sexual swelling and begin to mate. 

However, mating of adolescent females seldom results in pregnancy. Many females leave their natal group in adolescence and enter different groups. Females become adult after 13 years old and males after 16 years old. A female has her first baby around this age and thus her behaviors change accordingly. Males become larger than adult females and receive greeting vocalizations (pant grunts) from them. He now outranks some older males around this age.

Old Age and Death

We still do not have a concrete idea how long a chimpanzee lives. We know that some of them at least live over 50 years. But 50 years of research is still not enough to draw firm conclusion on the longevity of chimpanzees. Whether or not some chimpanzees might live up to 60 or even longer, only the future research will tell. Several females give births even in their 40s. The oldest record of giving a birth at Mahale is at her 50s.

Accumulation of such information enabled a research group to conclude that chimpanzees do not have menopause. However, one female at Mahale, Calliope, ceased to give birth in her late 30s and continued to live more than 10 years without reproducing. Thus, although some females continue to give births until late years of their life, other females may experience menopause. 

If we define 40 years as the old age for chimpanzees, there are relatively less old males compared to females. A male, Kalunde who lived up to 50s, looked really old in his last 10 years. His hairs became grey and sparse and he had many stains on his face. He obviously lost his physical strength and he was almost at the lowest-ranking among males. Still, he had a social influence on other younger and stronger males. He was frequently groomed by other males and was not punished even if he did not greet the higher-ranking males.

It is uncommon to see a chimpanzee’s death directly. Usually, researchers notice a long absence and retrospectively assume the death of the lost chimpanzee.

Daily Life of Researchers

A Day in the Field

At the research camp, I usually wake up while it is still dark. Because Mahale is at the western part of the Tanzania’s time zone, and also because there are mountains at the eastern side, it is only around seven o’clock am when day breaks in our research camp. It is still chilly in the morning. So first thing I do is to have a cup of hot coffee.

After quickly finishing the coffee and the breakfast and preparing for the field work, we start to the forest with Tanzanian assistants. First thing we do is to find chimpanzees. But actually, because we had followed them until evening the day before, we can easily know the approximate locations of them. We wait for vocalizations for a while, and usually within 10 to 15 min, there come noisy calls of pant hoots. 

As such, we start to observe chimpanzees and after that we basically follow them whole day in the forest. In my case, I usually stop observation between five o’clock and half past six pm. I finish my focal follow a bit earlier than chimpanzees make beds for sleeping because I need to look back to my field notes and recheck the data at camp, and because it is not so safe to walk in the forest after it becomes complete dark.

In the camp, a household assistant is preparing for hot water in buckets for bathing. After taking a sweat, I look back at my field notes and prepare for dinner. The assistant cooks the rice but we usually cook some side dishes in turn. Creating the variation of menu from the limited foodstuff is a good practice at the field.

After dinner I would have a bit of local liquor and talk with colleagues about the incidents that occurred today (of course about chimpanzees). Even though we have a long research history, there always happens something interesting. The talk is more of a gossip about chimps rather than academic talk about them.

Observing their Daily Life

Though the observation method is different depending on researchers and their research topics, at Mahale many researchers employ the focal observation method. It is a common observation method in the behavioral study of animals in that a researcher follows a particular chimpanzee for certain amount of time and record what happened to him/her during the follow. It is like stalking if we do this to a human but, fortunately, habituated chimpanzees do not seem to care if a human observer follows him/her even for an entire day (but it does not mean they do not care about humans at all). They do not, of course, wait for human observers thus can easily go into the dense bush or climb steep slope. We crawl in the bush or pant for breath to catch up with them. It is not uncommon that we completely lost the target.

Focal follow is usually recommended because the method makes it possible to objectively record all the behaviors in question. For example, if one wants to know how many hours a chimpanzee spends for grooming, this method is useful. While such objectivity is a reason for employing the focal observation method, I do this rather to “participate” in the society of chimpanzees. It is actually not possible to participate in everything they do, because we have different bodies with chimpanzees. We cannot easily climb trees to eat fruits nor can we participate in their grooming or in their fight. Thus, I participate in such activities through the eyes of my focal target by moving as same as possible as my target does and meeting other chimpanzees as she does.

Individual Identification

Another important method for observing animals is individual identification. In the early days of primatology, it was common for Japanese primatologists to identify monkeys only by their natural appearances, but was not always so for Western researchers. Now it is widely accepted method worldwide to identify primates just by their appearances and to name each individual.

I may not need to explain the merit of individual identification. It is better to look at a society with each individual identified rather than looking at a society with anonymous individuals. We casually do individual identification with each other in our daily life, and it is not possible to understand a drama occurring in the social world without knowing who is who.

Nevertheless, it may seem difficult for lay people to identify chimpanzees’ faces. But it is not a special ability to identify individual primates. At first, it is through some obvious characteristics such as a cut in an ear, scars in the face, lack of a finger, etc. Not all the individuals have such injuries so we also record subtler traits such as stains, wrinkles in the face, shape of bold area in the head, color of hair, shape of sexual skin, etc. After a while, we no more need to rely on such traits. With much subtler traits (thus it is often difficult to describe in language), we now identify an individual. Some individual may be identified even by their rumps or parts of limbs. Now it may be more proper to say that we “know” the individual rather than we “identify” the individual. When we become to “know” the individual, we do not need any identification marks such as scars. But we just can tell who is who. A known chimpanzee’s face is just her face. Nothing like other chimpanzees’ face.

Each chimpanzee has marked individuality. Actually any creature may have. Probably it may be a matter of observers who can understand its individuality or not and it may be easier for us to detect chimpanzees individualities than other species. While one is not capable of individual identification, individuality does not emerge. When one is ready to know the individual, already-existed individuality will appear to the eyes of the observer.

I often see that a tourist takes a lot of photographs with seemingly a very expensive camera and huge lens which look more like a bazooka, but only minority of tourists see the chimpanzees’ faces through binoculars. In my experience, watching a face well through binoculars is the best way to see their individuality. Why don’t you bring a pair of binoculars to the forest instead of a “bazooka”?


Endangered Chimpanzees

The research on chimpanzees is ongoing and should be continued for another half a century or more. But situations are not so optimistic. The chimpanzee in any region of their habitat is listed as “endangered” in the red list of IUCN. There have been several threats to the wild chimpanzees. First one is the destruction of their habitat. The second is the poaching on them for bush meat. The third is the capture of infants for pet trade. The forth is the demands for medical experiments. And the last one is transmission of disease through frequent contact with humans such as by research and tourism.

The first one is the most serious. Tropical forests in Africa that are the main home for the chimpanzees are decreasing with a considerable rate because of human economic activities, such as construction of roads for better access and transportation, needs of timber, cutting down trees for cultivation and firewood. The global warming may also influence the maintenance of tropical forests.

The fifth one is highly related to Mahale where the area is protected thus there are not so immediate threats on the forest destruction or poaching. Tourism that targeted chimpanzee viewing at Mahale was introduced in late 1980s and became more commercialized in 2000s, thus more and more people are coming to Mahale to see chimpanzees. It is often not emphasized to tourists that they can be the source of serious diseases to the wild chimpanzees. Because tourists come from all over the world, they may be infected with pathogens. If one has immunity from a disease, he may not show any symptoms, thus he may not be aware that he has a virus. Such a virus may be infectious to chimpanzees as we share common diseases, and may be fatal to them because they do not have immunity to such a virus from abroad. A tourist may not give up going to see chimpanzees if he is just slightly coughing, because he is there to see the chimpanzees by paying a lot of money. He will want to go as close to chimpanzees as possible just to have nice photos for uploading to his Social Networking Service. One should bear in mind that such slight egoism of each who sees chimpanzees will have a disastrous outcome for the wild chimpanzee population.

Actually in 2006, there happened an outbreak of respiratory disease in the Mahale M group and up to twelve chimpanzees died of the disease. Although it is often difficult to prove the source of the disease, from the observed pattern of spread of the infection, it seems the pathogen was brought from outside.

In the observation regulation, one who feels ill must not visit chimpanzees, and there is a distance permitted for tourists because taking certain distance may reduce the risk of droplet infection. Still the disaster took place. No one had malicious intention, but everyone might have thought “I cough slightly. But I feel OK. Why not see chimps in this precious occasion? “ or “Just one meter closer to have a better photo may not matter so much.” But such small selfishness might have brought twelve chimpanzees to die.

After the outbreak, researchers, tour company managers, and national park administrative gathered together to talk about the matter. We all agreed to strictly observe the viewing rules, such as the number limit in a tourist group, number limit for the tourist groups per day, and distance limit.

The Mahale Wildlife Conservation Society also proposed an additional rule that everyone should ware face masks. It is ideal that people do not go close to chimpanzees but humans seem still selfish. If everyone wears mask, that will also reduce the risk of droplet infection. The Conservation Society provided masks and asked all tourist camps to make their guests wear them. Now the face mask rule seems to take root and some tourist camp provide masks by their own costs. 

Of course, researchers are also not free of such rules. We now wear masks whole day when we are following chimpanzees in the bush. We strictly limit number of researchers to minimize the contacts to chimpanzees and we have also introduced one week quarantine before we start full observation of chimpanzees.

To the Future

In May 2014, a female called Puffy gave birth to a boy. She is a M group-born female.

Although most natal females go out from the M group, Puffy somehow stayed and gave birth in her natal group.

I have been familiar with Puffy since she was born, because her mother was my focal target. Puffy lost her mother in 2006 disease outbreak but survived the loss.

Thus I was more than happy to see her become a mother.

We now know that some wild chimpanzees may live more than 50 years. And as the baby being a male, he will stay in the M group if he survives. It is possible that after 50 years from now, the boy will still be alive as an elder. I will not see him that day, but will someone still continue to visit Mahale and to observe this young infant’s future when the Mahale research reaches its 100th year? Well, yes.

I truly hope that young generations will join the long-term ape research and conservation, and more of the history of the society of this wonderful animal will be elucidated.

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