Chimpanzee Pan troglodytes factsheet
Total population: 200,000 (wild), 1450 (captive)
Regions: Equatorial Africa
Gestation: 8 months (240 days)
Height: 816 mm (M & F)
Weight: 40 to 60 kg (M), 32 to 47 kg (F)
Species: P. troglodytes
Subspecies: P. t. schweinfurthii, P. t. troglodytes, P. t. vellerosus, P. t. verus
Other names: common chimpanzee, robust chimpanzee, Western or masked chimpanzee (P.t. verus), Central African or black-faced chimpanzee (P.t.troglodytes), East African or long-haired chimpanzee (P.t. schweinfurthii), Nigeria chimpanzee (P.t. vellerosus).
Some argue that chimpanzees should be categorized in the same genus as humans, Homo, based on the fact that chimpanzees and humans diverged only 4 to 6 million years ago (Groves 2001). The implications of changing the taxonomical categorization could have enormous impacts on how chimpanzees are perceived and the rights extended to them. For example, by categorizing chimpanzees as Homo, it might be considered unethical to keep them in zoos or use them in research.
Chimpanzees exhibit very little morphological differences between subspecies. They have a more robust build than bonobos (Pan paniscus) and are slightly sexually dimorphic with males, on average, weighing 40 to 60 kg (88.2 to 132 lb) and females, on average, weighing 32 to 47 kg (70.5 to 104 lb) (Rowe 1996). Males and females have an average height of 816 mm (2.68 ft) (Rowe 1996).
Chimpanzees are all black but are born with pale faces and a white tail tuft, both of which darken with age. They have prominent ears and both males and females have white beards.
Locomotion patterns include quadrupedal knuckle walking and occasional bipedalism. Chimpanzees are both terrestrial and arboreal, with the amount of time spent on the ground varying between study sites and between sexes (Doran 1996).
All chimpanzees build sleeping nests in trees at night (Rowe 1996).
The average lifespan of chimpanzees is 40 to 45 years, though it is considerably longer for captive chimpanzees (Macdonald 2001).
CURRENT RANGE MAPS (IUCN REDLIST): Pan troglodytes
Chimpanzees are found across a west-east belt in equatorial Africa. Their range spans 22 countries: Angola, Burkina Faso, Burundi, Cameroon,Central African Republic (CAR), Congo, Côte d’Ivoire, Democratic Republic of Congo (DRC), Equatorial Guinea, Gabon, Ghana, Guinea, Guinea Bissau, Liberia, Mali, Nigeria, Rwanda, Senegal, Sierra Leone, Sudan, Tanzania, and Uganda (Butynski 2001; Nishida et al. 2001). This represents a total area of about 2.5 million km² (965,255 mi²) though the majority (about 77%) of the total estimated population can be found in only two countries, Gabon and Congo (Cowlishaw & Dunbar 2000). Odzala National Park, Congo boasts the highest population density of chimpanzees in Central Africa with 2.2 individuals per km² (1.37 per mi²) while Gabon has the largest population (Bermejo 1999; Butynski 2001). Researchers roughly estimate the wild population of chimpanzees to be between 100,000 and 200,000 (Nishida et al. 2001). There are approximately 250 animals in zoos and another 1,200 in research facilities (Goodall 2001).
Chimpanzees have been studied at 41 sites, but there are a few long-term study sites and notable scientists that have been sources of invaluable discoveries about chimpanzee biology, society, and culture. In 1960, Jane Goodall began the first long-term study of wild chimpanzees (P.t. schweinfurthii). Her research in Tanzania at Gombe Stream National Park led to significant discoveries about social relationships, tool-use, and warfare in chimpanzee societies. At another site in Tanzania, Toshisada Nishida began a long-term research project on the chimpanzees (P.t. schweinfurthii) of the Mahale Mountains National Park. Christophe and Hedwige Boesch have headed the research on chimpanzees (P.t. verus) in Taï National Park in Côte d’Ivoire since 1976. Other important study sites include Bossou, Guinea and sites in Uganda including the Ngogo study site in Kibale National Park and Budongo Forest Reserve.
Because of their broad distribution, chimpanzees live in a wide variety of habitat types that includes dry savannas, evergreen rainforests, montane forests, swamp forests, and dry woodland-savanna mosaics (Goodall 1986; Fruth et al. 1999; Poulsen & Clark 2004). To live across such different habitat types, chimpanzees must be quite adaptable. In low-altitude rainforests, there is little change in temperature from season to season, the humidity is always high, and there are few dry days each year. In contrast, the arid areas, including the north and southeastern limits of their range (Senegal and Tanzania, respectively), show huge fluctuations in temperature and humidity throughout the year as well as long dry periods (Goodall 1986). Another dry habitat where chimpanzees have been studied is Semliki, Uganda, where average annual rainfall is 1206 mm (3.95 ft) and maximum temperatures reach 34°C (93.2°F) (Hunt et al. 2002).
Characterizations of temperature and rainfall are mostly available for sites where long-term research is being conducted. Gombe and Mahale are similar in climate and character, though Mahale is slightly more humid with more woodlands and higher mountains (Boesch & Boesch-Achermann 2000). Gombe is made up of steep ridges and valleys bordering Lake Tanganyika, one of Africa’s Great Lakes. There is marked seasonality here, with the wet season spanning from mid-October to mid-May, and the rest of the year being quite dry. Daily temperatures range from 18.5°C to 30°C (65°F to 86°F) throughout the year, with August and September being the hottest months (Goodall 1986). Because of the dramatic
changes in elevation at Gombe, there are a variety of vegetation types throughout the park: subalpine moorland, open woodland, semideciduous forest, evergreen forest, grassland with scattered trees, and beach (Goodall 1986). At Bossou, the major part of the core area utilized by chimpanzees consists of multi-stage secondary deciduous forest arising in plots abandoned after shifting agriculture. The other areas at Bossou are primary forest and grasslands (Sugiyama & Koman 1987). The chimpanzees at Taï inhabit the only remaining tropical rainforest in Côte d’Ivoire (Boesch & Boesch-Achermann 2000). While there is no true dry season, the rainy seasons are from March to June and between September and November, and the average minimum temperature is 18°C (64°F) (Boesch & Boesch-Achermann 2000).
The chimpanzee diet consists mainly of fruit, but they also eat leaves and leaf buds, and the remaining part of their diet consists of a mixture of seeds, blossoms, stems, pith, bark and resin (Goodall 1986). Chimpanzees are highly specialized frugivores and across all study sites preferentially eat fruit, even when it is not abundant. They supplement their mainly vegetarian diet with insects, birds, birds’ eggs, honey, soil, and small to medium-sized mammals (including other primates) (Goodall 1986; Boesch & Boesch-Achermann 1989; Isabirye-Basuta 1989). Their most common mammalian prey is the red colobus monkey (Procolobus badius), though they also eat blue duikers, bushbucks, red-tailed monkeys (Cercopithecus ascanius), yellow baboons (Papio cynocephalus cynocephalus), and warthogs (Boesch et al. 2002). Chimpanzees spend, on average, half of their days feeding, and much time moving from one food source to the next (Goodall 1986). The actual time spent feeding, though, is correlated with the amount of processing time required by the type of food being consumed.
The use of tools to obtain some foods has been documented across all chimpanzee populations. Sticks, rocks, grass, and leaves are all commonly used materials that are modified into tools and used to acquire and eat honey, termites, ants, nuts, and water. While these implements may seem too crude to be considered true tools, there certainly is evidence that forethought and skill are required to make and use them and lack of complexity should not detract from the fact that they are still tools (Boesch & Boesch 1993). For example, to extract honey from the hives of stingless bees, chimpanzees use short sticks stripped of their leaves, twigs, and bark to most effectively scoop it out of the hive. On the other hand, to extract honey from the hives of aggressive African honeybees, chimpanzees use significantly longer and thinner sticks to avoid the painful stings of these bees (Stanford et al. 2000). In a similar fashion, chimpanzees strip the leaves off of long, thin sticks and use these to extract ants from ground nests (Goodall 1986; Boesch & Boesch 1993). This practice requires some amount of skill, and infant and juvenile chimpanzees must practice a great deal before mastering the technique necessary to extract the ants still clinging to the thin, flexible tools. In fact, some chimpanzees never fully master the skill of ant dipping, and in general, females are more successful than males in this endeavor (Goodall 1986; Boesch & Boesch 1993). A similar tool and technique is used to extract termites from nests at Gombe, but at Taï, the chimpanzees simply use their hands (Boesch & Boesch 1993).
Using a hammer and anvil tool set made of fallen branches or hand-held stones and exposed tree roots or rocky outcroppings, chimpanzees in West Africa crack hard nuts (Boesch & Boesch 1993; Boesch & Boesch-Achermann 2000). Often these items are not found together or near a source of nuts, so nut-cracking chimpanzees must exhibit forethought to gather the appropriate accoutrements to eat these important high-protein, high-fat foods. Like ant fishing, nut cracking is a skill that must be learned, and infants and juveniles must learn from their mothers the appropriate tools and movements to shell nuts (Boesch & Boesch-Achermann 2000).
Chimpanzees also use leaves as sponges or spoons to drink water. Selectively choosing the type of leaf to use, chimpanzees crumple these leaves in their mouths and then submerge them in water; the crumpled leaves act like a sponge and they suck the water out of them and repeat the process (Sugiyama 1995). This behavior is especially prevalent where water is scarce at certain times of year and it is so deep in tree holes that chimpanzees cannot easily access it directly with their mouths.
Chimpanzees have excellent mental maps of their home ranges and use these to locate food resources repeatedly. Their attention may be directed to a new food source by a noisy group of animals, such as birds or other primates, or they may be led to a new fruit tree or termite mound by a foraging companion that has been there before (Goodall 1986).
Long thought to be free of natural predators because of their large body size, work in the Taï Forest and at Lopé National Park, Gabon has shown that leopard (Panthera pardus) attacks can be a significant cause of mortality in chimpanzees (Boesch &Boesch-Achermann 2000; Henschel et al. 2005). The extent to which leopards choose to hunt chimpanzees is unclear, though, and may be the work of just a few risk-taking cats (Boesch & Boesch-Achermann 2000). Lions are also capable of killing chimpanzees, and predation by lions has been observed at Mahale Mountains National Park in Tanzania, but there are scant observations of lion predation at other sites where they are sympatric with chimpanzees (Tsukahara 1993).
Content last modified: April 13, 2006
Written by Kristina Cawthon Lang. Reviewed by Elaine Videan.