Bonobo Pan paniscus factsheet
Total population: 50,000-100,000
Regions: Democratic Republic of Congo
Gestation: 8 months (240 days)
Height: 730 to 880 mm (M), 700 to 760 mm (F)
Weight: 39 kg (M), 31 kg (F)
Species: P. paniscus
Other names: bonobo chimpanzee, gracile ape, lesser chimpanzee, or pygmy chimpanzee; chimpanzeé nain or chimpanzeé pygmée (French); chimpancé pigmeo (Spanish); bonobo or dvärgschimpans (Swedish). The name bonobo is meaningless; it is probably derived from a misspelling on a shipping crate going to Bolobo, Zaire (now Democratic Republic of Congo) (de Waal 1997).
Bonobos are sometimes called pygmy chimpanzees even though they are about the same size as chimpanzees (Pan troglodytes). Overall, they have a more gracile, or slender, build than chimpanzees. They exhibit moderate sexual dimorphism with adult males weighing about 39 kg (86.0 lb) and, on average, measuring 730 to 830 mm (2.40 to 2.72 ft) tall while adult females weigh about 31 kg (68.3 lb) and are about 700 to 760 mm (2.3 to 2.49 ft) tall (Rowe 1996).
Bonobos have black hair and black faces from birth. The hair on their head looks as if it is parted and they do not tend to go bald with age as is seen in chimpanzees. Bonobos are also born with a white rump tuft (Rowe 1996; de Waal 1997).
Locomotion patterns in bonobos include quadrupedal knuckle walking, modified brachiation and some bipedalism (Rowe 1996). Bonobos show a greater predisposition for bipedal gait than other apes because of a more centrally positioned foramen magnum, longer thigh bones, longer feet, and differential distribution of body weight (Myers Thompson 2002).
The average lifespan of bonobos is 40 years (Rowe 1996).
Bonobos are confined to a 200,000 km² (77,220 mi²) area in central Africa in the Democratic Republic of Congo (DRC). This area, roughly the size of Great Britain, in the central basin of the DRC, contains two river systems that converge to define the extent of bonobo distribution: the Congo-Zaire-Walaba River and the Kwa-Kasai-Sankuru River (Kortlandt 1995). These rivers serve as an effective geographical barrier for the apes as they are not known to swim (though they have been seen wading into waist-deep water) (Kortlandt 1995; Myers Thompson 2002). IUCN Redlist estimates a minimum range size of 500,000 km² (IUCN Redlist).
Estimates of wild populations are few and varied, with numbers as low as 5,400 up to 100,000 individuals (Kortlandt 1995; Thompson-Handler et al. 1995). These numbers may be considered overly optimistic, though, and the true population size is unknown (Coxe et al. 2000). IUCN Redlist reports a population estimate of at least 29,500 individuals (IUCN Redlist). There are about 150 individuals in captivity (ISIS.org).
Most fieldwork has been conducted in two sites, Lomako and Wamba, but other research sites include Lilungu (Ikela), Yalosidi, Yasa, and Tumba. The bonobos at the Wamba study site have been observed since 1974 and are provisioned with food such as sugarcane (de Waal 1997).
Bonobos exploit the swampy rainforest south of the Zaire River. They forage in swamp meadows on a thin underlying peat layer. The semideciduous trees that this area supports produce fleshy fruits adapted to mammal dispersion. These trees are part of a secondary
forest ecosystem and are generally in intermediate and older stages of development. These forests are also known as subclimax forests (Kortlandt 1995). At one of the field sites, Lukuru, there is an absence of swamp vegetation and bonobos utilize the mosaic of dry forest and savanna habitats (Myers Thompson 2002).
The average monthly air temperature in this region is between 20° to 30° C (68° to 86° F). The annual rainfall in this area is between 1600 and 2000 mm (5.25 and 6.56 ft) (Kano 1992).
The population density of bonobos is hard to estimate, but some studies have put it at 0.4 individuals per km² (.249 per mi²) (Kano 1992; Kortlandt 1995). Even in the most densely populated areas, these apes have a patchy distribution.
Their diet consists mainly of plant products including fruit, seeds, sprouts, leaves, flowers, bark, stems, pith, roots, and mushrooms.
Though the majority of their diet is fruit (57%), bonobos are also known to consume small mammals, insect larvae, earthworms, honey, eggs, and soil (Kano 1992; Bermejo et al. 1994). Unlike chimpanzees, bonobos do not actively hunt mammalian prey but feed on it opportunistically (White 1996). At one study site, bonobos have been observed washing off their food before eating (Bermejo et al. 1994).
Daily activities can be partitioned into six categories: feeding in trees, rest, travel, foraging, nest-building, and group excitement.
These daily activities are generally in a cycle of resting (43% of the day), traveling (13%), foraging (20%), and feeding (20%). The remaining time is spent doing other activities. Bonobos forage for principal food items between 25 and 40 m (82 and 131 ft) above the ground. Though
most primary food sources are found at this height, they will not ingest food found at this height if there is not a secure substrate (Kano 1992). Their average daily travel distance is 2.0 km (1.24 mi) (Kano 1992).
Because of the relative richness of their habitat and availability of food sources, there is little constraint on bonobo group size. The result is a decrease in intraspecific feeding competition and heightened sociality, especially between females (Blount 1990).
Written by Kristina Cawthon Lang. Reviewed by Frans de Waal.
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