CHIMPANZEES source Jane Goodall Institute:

TAXONOMY & DESCRIPTION

The robust or common chimpanzee is a large ape belonging to the order of primates, and the family hominidae, which also includes the gorilla, orang-utan, and bonobo. Chimpanzee males are smaller than the male orang-utan or gorilla. The females have similar body measurements to female orang-utan. The average male head-body length measurement is 850mm and weight range is between 40-60kgs for males and 33-46kg for females.

The current consensus is that there are two species of chimpanzees; Pan troglodytes and Pan paniscus. There are four subspecies of the robust or common chimpanzee; Pan troglodytes verus; Pan troglodytes vellerosus; Pan troglodytes troglodytes and Pan troglodytes schweinfurthii, and at this stage no subspecies is recognised for the gracile chimpanzee, better known as the Bonobo or Pygmy chimpanzee Pan paniscus.

Chimpanzee pelage is generally black, though individuals with brown pelage have been observed, which can go grey with some individuals upon maturity. Skin colouration varies with age. Infants are often born with pale skin, which gradually darkens as they become adults. Generally as the chimpanzee matures the skin becomes black though sometimes individuals retain a pale skin and some will have freckles.

DISTRIBUTION & ABUNDANCE

The historical chimpanzee range was at least 25 countries throughout Equatorial Africa. Today, chimpanzees occur in 22 countries from 13oN to 7oS latitude. The present range covers an area of approximately 2,342,000kmsq, but distribution and numbers are poorly known in most areas. There is a vast difference in the geographic and known ranges of the four sub species of chimpanzees. While data relating to the distribution and approximate number of chimpanzees in some countries exist, many populations have not been surveyed or have only had isolated surveys in some forest blocks as they are of interest to particular conservation organisations.

While there has been an effort made in the past five years to carry out surveys in many countries, there have been very few countrywide censuses where forests have been extensively surveyed.

The West African sub species (P. t.verus) occurs in 10 countries in West Africa. The current known populations are fragmented and declining in numbers. Historically, P. t.verus were believed to have occurred in 12 countries. The geographical ranged was 631,000kmsq with an estimated population range from 21,000 to 55,000.

The recent identification of a new subspecies P.t.vellerosus includes the population of chimpanzees straddling the northern border of Cameroon and the Southern border of Nigeria between the Niger River and Sanaga Rivers (into this subspecies). They have a relatively limited range of 142,000kmsq. The estimated number for this subspecies is between 5,000 and 8,000 individuals.

The range of central African subspecies (P .t. troglodytes) range extends across seven countries from Cameroon in the north to the Congo River in Peoples Republic of Congo (PRC)). The largest population of this subspecies is found in Cameroon and Gabon, while substantial population exist in PRC. Smaller populations are present in Equatorial Guinea, The Central African Republic (CAR), northern Angola and the extreme west of Democratic Republic of Congo (DRC). The known geographic range is approximately 695,000kmsq. The central African chimpanzee population is estimated to be between 70,000-116,000 individuals. This subspecies is found in some of the most undisturbed habitat remaining. The eastern chimpanzee (P.t.schweinfurthi) occurs in seven countries with a geographic range of 874,00kmsq.

HABITAT

Equatorial Africa contains a multitude of landscape ecosystems including multi-strata tropical forest, dry deciduous forest, woodland, mosaic grassland forests, savannah woodlands, savannah, and desert. The robust chimpanzee has adapted to living in a variety of these habitats, including mosaic grassland forests, savannah woodlands and tropical moist forests. Chimpanzees also occur at altitudes ranging from sea level to around 2,899m in elevation. The tropical zone of Africa is reported to be drier than the tropical zones of Asia and America. Only a few regions receive more than 2500mm of rainfall per year. Many of these forests lie close to the equator and therefore receive two rainy and two dry seasons per year. It is suggested that the forests of Africa were fragmented by dry forests or woodland prior to human clearing activities. This is one possible explanation for the adaptive nature of chimpanzees, as evidenced by their ability to utilize these drier forests. These habitats are marginal habitats for chimpanzees as sourcing water can limit the ability of chimpanzees to survive in such habitats.

Feeding behaviour in chimpanzees varies seasonally and is greatly influenced by food availability and habitat type. The feeding repertoire of chimpanzees over their range shows many differences, some of which cannot be explained by variation in their biotic environments. They reflect traditional and possibly cultural variants between communities. There are also differences in food processing techniques and the use of plants for self-medication purposes.

Chimpanzees are omnivorous and have a diverse diet. Fruit usually comprises the largest portion of their diet but they are also known to eat flowers, bark, roots and tubers, tree gum and insects such as adult termites (Isoptera sp.), ants (Dorylus sp. and Oecophylla longinoda), and the larvae and eggs of ants, bees and several species of beetles such as the Raphia coleopteran and Rhyncho­phorus quadrangulus.

Different communities vary in the diversity of their dietary repertoire and the proportion of low-quality foodstuffs they consume. They also incorporate different insect prey into their diet, with some being ignored at some sites while consumed at others.

Hunting by chimpanzees is usually confined to males and prey is usually captured opportunistically. They prey on duikers, young bushbuck, baboons and other monkeys. However, these same species can often be seen near chimpanzees that ignore them. Attacks are usually quick and well coordinated and generally successful. Intense excitement is often evident during hunts followed by intense competition for the spoils, as usually, there is not enough to be shared, with the killer having full rights to the meat and the remainder chimpanzees begging. Infanticide by adult males has also been observed with the infants being eaten.

COMMUNICATION

Like people, chimpanzees communicate in various ways. They communicate with body language (positions and gestures), facial expressions and vocalizations. There are intraparty calls (calls among chimps that are in a group together) and distance calls (calls made between groups that are separated, sometimes over a great distance). Below are some calls that chimpanzees make and the emotions that go with them.

Table 1: Chimpanzee Calls

Soft Bark, or cough

The food calls, a mixture of food grunts, barks and pant hoots, alert other chimpanzees to the whereabouts of food sources. A special intensity of excited calls of this type indicates that there has been a successful kill after a hunt.

Each individual has his or her own distinctive pant-hoot, so that the caller can be identified with precision.

A loud, long, savage-sounding wraaaa call is made when a chimpanzee comes across something unusual or dangerous.

When young chimpanzees play, they emit breathy laughter.

Soft grunts uttered by foraging or resting chimpanzees probably serve to maintain communication within the group.

Posture, gestures, and facial expressions communicate many messages and emotions within a group. When greeting a dominant individual after an absence or in response to an aggressive gesture, nervous subordinates may approach with submissive signals - crouching, presenting the rump, holding their hand out, accompanied by pant-grunts or squeaks. In response, the dominant individual is likely to make gestures of reassurance, such as touching, kissing, or embracing the subordinate.

Friendly physical contact is crucial in maintaining good relationships among chimpanzees. For this reason, social grooming is probably the most important social behaviour, serving to sustain or improve friendships within the community and to calm nervous or tense individuals.

The grin of fear seen in frightened chimpanzees may be similar to the nervous smiles given by humans when tense or in stressful situations. When angry, chimpanzees may stand upright, swagger, wave their arms, throw branches or rocks - all with bristling hair and often while screaming or with lips bunched in ferocious scowls.

Male chimpanzees proclaim their dominance with spectacular charging displays during which they slap their hands, stamp with their feet, drag branches as they run, or hurl rocks. In doing so, they make themselves look as big and dangerous as they possibly can, and indeed may eventually intimidate a higher-ranking individual without having to fight.

Table 2: Chimpanzee Facial Expressions

Chimpanzee Facial Expressions supporting graphic

FEEDING BEHAVIOUR

Feeding behaviour in chimpanzees varies seasonally and is greatly influenced by food availability and habitat type. The feeding repertoire of chimpanzees over their range shows much variation, some of which cannot be explained by differences in biological environments. The differences in feeding behaviour also reflects traditional and possibly cultural variants among communities. There are also differences in food processing techniques and the use of plants for self-medication purposes.

Chimpanzees are omnivorous and have a diverse diet. Fruit usually comprises the largest portion of their diet but they are also known to eat flowers, bark, roots and tubers, tree gum and insects such as adult termites (Isoptera sp.), ants (Dorylus sp. and Oecophylla longinoda), and the larvae and eggs of ants, bees and several species of beetles such as the Raphia coleopteran and Rhynchophorus quadrangulus.

Different communities vary in the diversity of their dietary repertoire and the proportion of low-quality foodstuffs they consume. They also incorporate different insect prey into their diet, with some being ignored at some sites while consumed at others.

It is mostly the male chimpanzees who hunt, and they tend to do so opportunistically. They prey on duikers, young bushbuck, baboons and other monkeys. However, chimpanzees often spend time peacefully near these species, virtually ignoring them. Attacks are usually quick and well coordinated and generally successful. Chimpanzees become intensely excited during hunts, and engage in intense excitement for the spoils. Normally, there is not enough to be shared. The killer has full rights to the meat and the other chimpanzees are left begging. Infanticide by adult males has also been observed with the infants being eaten.

TERRITORIAL AND LETHAL AGGRESSION

Chimpanzees are well known for their territorial behaviour. They are among the few animals that engage in between-group coalition aggression that results in fatalities. Encounters between communities typically take place during boundary patrols.

Communities defend an area within the forest known as a territory. This differs from the home range of an individual, which is not defended but remains within the territory of the community in which the individual lives. Males will form border patrols and walk the perimeter of their communtys territory looking for neighbouring community members who might try to invade their territory. The main difference between the robust or common chimpanzee and other primate multi-male groups is that in the former, the males remain in their natal communities while females may disperse to neighbouring communities, usually once they have reached sexual maturity. This allows male chimpanzees to form strong bonds and results in close genetic ties. As a male-dominant, hierarchical species, these alliances between individuals may allow them to achieve high ranks within the community. Several factors influence territory size, including the number of individuals in the community, habitat quality (with regard to food availability and quality), pressure from neighbouring communities, and population density.

MIGRATION / DISPERSAL

Chimpanzees live in a multi-male social system; one of three main social grouping types recognised in primates. They have a relaxed form of this type of system, commonly referred to as a fission-fusion society. The fission-fusion system allows the community to disperse in smaller parties that constantly change in size and composition throughout the day. This allows them to group, regroup and separate during their daily quest to find food, to maintain social relationships and to protect their territory.

Adult cycling females, and more commonly adolescent females, show a strong tendency to disperse into the range of adjacent or non-adjacent communities (i.e communities/ populations other than their own that occur beyond their own community home range). They may leave their natal community permanently or temporarily when they are in oestrus, and are attracted to high-ranking males in neighbouring communities. Males remain in their natal group from birth until death, (but there are exceptions) or transfer with their mothers into neighbouring communities as juveniles. Dispersal may be influenced by the carrying capacity of the home range, distance to other communities, sex ratios, and the genetic structure of the population. Evidence suggests that females avoid mating with close relatives, which may also promote dispersal.

LOCOMOTION

Chimpanzees use various methods of locomotion. They are both terrestrial and arboreal. Brachiation, climbing, bipedalism and quadrupredal knuckle-walking can all be observed in chimpanzees. They will feed and rest on both the ground and in the trees, although generally they will travel long distances on the ground. This habit of travelling on the ground has made chimpanzees and gorillas vulnerable to snares set by hunters.

NEST BUILDING

Chimpanzees build nests to sleep in, normally building one nest each night, unless they reuse a nest from a previous night or occupant. Chimpanzees build arboreal nests and use a foundation of solid side branches or forks, bending, breaking and inter-weaving the branches cross-wise, generally constructing the nest in a circular fashion. Chimpanzees will occasionally build day nests as well, building nests on the ground. This nest building habit has proven to be very useful to researchers who have found it to be the most practical and accurate way of estimating population size of unhabituated chimpanzees.

REPRODUCTIVE BEHAVIOUR

Reproduction in chimpanzees is similar to humans. At this stage, the average number of infants a female can produce in a lifetime is not known. Chimpanzees are considered to be a K-strategist species, meaning they have delayed onset of reproduction and produce few, large young in which the parents invest heavily. K-Strategists are often unable to rebuild their populations fast enough to avoid extinction following a major decline in population numbers.

Copulation can occur at any point in the females oestrous cycle. Males may guard females from mating with other males. This can cause tension amongst males, and in some cases consortship behaviour will be observed; the male entices a female to leave the core area and they travel together away from the other community members until her cycle has completed.

Menstrual cycles last on average 39.8 days for young nulliparous females (those who have never borne a child) and 33.8 days for older multiparous females (those who have borne more than one child). Females exhibit their first sexual swellings at around 10-11 years, with an average swelling of 12-13 days. Duration of gestation ranges from 208 days to 235 days, with an average of 225.3 days. Mating is generally promiscuous although consortship's involving just one male and one female have been recorded. Inter-birth intervals range from 3-7 years. The longest ongoing field study of chimpanzees is Jane Goodall's research station in Gombe Stream National Park, with continuous observation of a wild chimpanzee community spanning 45 years. Some of the females that were born at the time of Jane Goodall's arrival are alive and still reproducing. This suggests that wild living chimpanzees may go through menopause at a much later age than first thought. Several female chimpanzees in captivity that are no longer cycling are all over fifty years of age.

MOTHER-INFANT BEHAVIOUR

Mothers care for their offspring for an extended period of time and infants are totally dependant on their mothers for 6-7 years. Some still require their mothers support emotionally as they mature and become independent. Due to this close physical and emotional relationship between mother and infant, the removal of an infant from the wild to supply zoos, laboratories and animal dealers can only be carried out by killing the mother. This has contributed to a significant loss of females and infants from in-situ populations.

PLAY

Infants and juvenile spend at least 5% of their time playing each day. Adults sometimes play with infants, and even with each other, but this is less common. Play is usually accompanied by a play face, and when play becomes boisterous, chimps laugh. Play includes tickling, wrestling and chasing and sometimes incorporates objects such as leafy twigs, sticks, stones and large fruit. Sometimes infants will play on their own.

TOOL USE AND TOOL MAKING

Chimpanzees make and use a diverse and rich kit of tools and, with the exception of humans, they are the only living primates to consistently and habitually use and make tools. Each community of chimpanzees has a unique repertoire of tool use behaviours that may differ from that of other communities. Tool use in chimpanzees may serve several purposes including extracting, probing, body cleaning, displaying and pounding. A total of 51% of tools employed by wild chimpanzees are used in a feeding context, while 17% are used in aggressive contexts against conspecifics or other species (mainly leopards, snakes or even humans), 12% are used for communication purposes, 11 % are used to inspect the environment and 9% are used to clean their own bodies.

Cracking is probably the most sophisticated one performed by chimpanzees and has only ever been observed among some populations of the West African subspecies of chimpanzee, although nut-bearing tree species are available at many sites where chimpanzees have been studied else­where in Central and East Africa.

Tool use in chimpanzees has been shown to play an important role in survival by enabling them to exploit food resources that would be otherwise difficult to access. The other tool use behaviours reported so far include the use of wands to dip for driver ants Dorylus sp. (Chimpanzees may also use a digging stick to dig up the underground nests of these ants) or as probes to fish for termites from their mounds Macrotermes sp.

Studies of chimpanzees in different regions of Africa have revealed that chimpanzee communities exhibit different tool use behaviours and may use different tools for the same purpose at different sites. Nut cracking behaviour is pervasive only in a very small area within the evergreen forest perimeter of West Africa, more precisely west of the N'Zo Sassandra River, which seems to demarcate the eastern limit of its distribution. Chimpanzees clearly demonstrate the ability to fashion tools adapted for the specific purpose of their task and demonstrate variability across sites in their use of raw materials for tool manufacture. Not all of this regional and local variation can be explained by the demands of the physical and biotic environments in which they live. These variations in tool use behaviour have been suggested recently to represent cultural behaviours.

SLEEP

Each evening, chimpanzees construct a fresh "sleeping nest" in the trees where they will curl up and sleep. These bowl-shaped nests are made out of leaves and other plant material. Nests are only shared by a mother and her nursing offspring.

GROOMING

During times of relaxation, a chimpanzee may often be found grooming another chimpanzee or its own hair. The most obvious function is the removal of pieces of debris from soil, vegetation and dried skin or parasites from the hair. The chimpanzee uses one hand to hold the hair back while the other hand, lips, or teeth are used to pick out and remove the small pieces of debris.

Grooming is also used to relax tension from threats and aggression. It helps to maintain friendly ties among family and community members and to lessen the stress of infants during weaning. A chimpanzee may request or solicit grooming by approaching another chimpanzee and getting their attention by presenting a part of its body for grooming. It may scratch itself or start to groom itself. Grooming is a very important social and skin care behaviour. A grooming session may include several individuals of varying ages and continue for a few seconds, minutes, or hours.

Daily time spent on specific behaviours

SOCIAL INTERACTIONS

Chimpanzees are a very social species within their communities, this is important to their daily and long-term behaviour; however this can also extend to other animals.

INTER-SPECIES INTERACTIONS

Within chimpanzee communities, individuals are very tolerant of each other with fighting or aggression rarely seen to be intense enough to cause death of a community member. It is important for communities to have strong social bonds with each other to ensure their welfare. However, such hospitality does not usually extend to neighbouring communities. Chimpanzees are very territorial and protective of their communities. Males and sometimes females or juveniles, are known to go on 'patrols' of their borders to ensure other chimpanzees males and sometimes even females, do not enter. When such groups encounter other individuals, fighting regularly leading to death can occur. These patrols may benefit a community by extending boundaries, protecting members and incorporating females.

Chimpanzees co-exist with many other species of animals, including other primates such gorillas, baboons and several monkey species. However, they rely generally on different key food items, and mutually avoid contact. Interactions with other animals can vary in their response. Species such as large antelopes are regularly ignored. Other animals, which are potential predators such as leopards are feared and generally avoided. A few species can be seen as potential food sources, such as colobus monkeys and may be actively hunted if the opportunity arises. Chimpanzees have even been noted to capture and toy with species such as squirrels and tree hyraxes, but neither being regarded as prey animals. However, on the rare occasion is has been seen that chimpanzees may socially interact with other species. At Gombe, one young chimpanzee was found to play with a young baboon. Such interactions are only likely to develop in juveniles and not continue into adulthood.

BEHAVIOURAL PATTERNS IN CHIMPANZEES

With increasing study of wild chimpanzees, researchers have noticed that different populations of chimpanzees exhibit different behaviours, not always associated with factors in their environment. Like humans, chimpanzees show cultural diversity, with chimps living in different parts of Africa developing distinct customs i.e. different communities will show different methods of response for the same behaviours or behaviours observed in only one population.

SOME TYPES OF CULTURES INCLUDE:

NUT CRACKING

In West Africa, chimpanzees at several locations use wood or stone tools to crack nuts to feed on the kernels. In East Africa, although nuts are available, chimps don't eat them.

GROOMING

Some chimps inspect each other for parasites, flick the bugs on to leaves, then inspect or kill them. However their neighbours show quite different behaviour, simply squashing the parasites on their forearms.

TERMITE FISHING

In Gombe National Park in Tanzania, termite mounds of red earth rise 2 meters high and shelter millions of the almond-colored insects. Chimpanzees pore over the mounds, scratching at plugged tunnels until they find portals into the mound's interior. They will gently insert a twig or blade of grass into a tunnel until the soldier termites latch onto the tools with their powerful mandibles, then they'll withdraw the probe from the mound. With dozens of soldier and worker termites clinging ferociously to the twig, the chimpanzee draws the stick between her lips and reaps a nutritious bounty. Less than 100 kilometers away from Gombe's termite-fishing apes is another culture. Chimpanzees in Mahale National Park live in a forest that is home to most of the same species of termites, but they practically never use sticks to eat them. If Mahale chimpanzees forage for termites at all, they use their fingers to crumble apart soil and pick out their insect snacks. However, Mahale chimpanzees love to eat ants. They climb up the straight-sided trunks of great trees and poke Gombe-like probes into holes to obtain woodboring species. As adept as Gombe chimpanzees are at fishing for termites, they practically never fish for these ants, even though both the ants and termites occur in both Gombe and Mahale. In West Africa, chimpanzees do not use stick-tools at all.

HUNTING

There is a culture of hunting in each forest as well. At Gombe, for instance, chimpanzees relish wild pigs and piglets in addition to monkeys and small antelope. At Tai in West Africa, wild pigs are ignored even when they stroll in front of a hunting party.

Source Jane Goodall Institute www.jgiuganda.org