Pan paniscus
bonobo
(Also: pygmy chimpanzee)

Bonobos (Pan paniscus) live in the forests located centrally in the Democratic Republic of the Congo (formerly Zaire). Bonobo habitat lies in the Congo Basin. This area is located south of an arc formed by the Congo River (formerly the Zaire River) and its headwater, the Lualaba River, and north of the Kasai Rver. (Kano, 1982; Kano, 1983; Kano, 1992)

Within the Congo Basin, bonobos inhabit several vegetation types. The area generally is classified as tropical rainforest; however, local agriculture and areas reverted to forest from agriculture (“young” and “aged secondary forest”) are intermingled. Species composition, height, and density of trees are different in each, yet all are utilized by bonobos. In addition to the forested areas, swamp forests opening into marsh-grassland areas occur, which are also utilized. Foraging occurs in each type of habitat, while sleeping occurs in forested areas. Some bonobo populations may have a preference to sleep in relatively small (15 to 30 m tall) trees, particularly those found in secondary growth forests. (Fruth and Hohmann, 1993; Kano, 1983; Kano, 1992; Uehara, 1988; Uehara, 1990)

Contrary to the implication of one of its common names, "pygmy chimpanzee," this species is not particularly diminutive when compared to common chimpanzees (Pan troglodytes). The "pygmy" modifier may instead refer to its location: it lives in an area inhabited by people often referred to as such.

Unlike its closest cousins (common chimpanzees), bonobos are not divided into subspecies. Bonobos are apes about two-thirds the size of humans, with dark hair covering their bodies. The hair is generally longer than in common chimpanzees, and is particularly noticeable on the cheeks, which are relatively hairless in P. troglodytes. The portions of body not covered with hair (i.e. mid-face, hands, feet) are darkly colored throughout life. This contrasts with common chimpanzees, which have lighter skin, particularly during the younger years.

Bonobos are primarily knuckle-walkers, although at times they walk bipedally and do so more frequently than P. troglodytes. Bonobos have longer extremities, particularly hind legs, as compared to common chimpanzees. Although sexual dimorphism exists with males around 30% heavier (37 to 61 kg, 45 kg average) than females (27 to 38 kg, 33.2 kg average), bonobos are less sexually dimorphic than many primates, and skeletons are nearly the same size. Average height is 119 cm for males and 111 cm for femals. Average cranial capacity is 350 cubic centimeters. (Boesch, 2002; Jungers and Susman, 1984; Kano, 1992; Zihlman, 1984)

Limited information exists on bonobo longevity, and there has been no ongoing study that lasted longer than the expected bonobo lifespan. The longest semi-continuous study of bonobos began at Wamba in 1976. At that time, the age of each individual was estimated, and from extrapolation, a female that died in 1993 was in the 45 to 50 year age range when she died. This would make the lifespan of these animals comparable to that of common chimpanzees. (Furuichi et al., 1998; Furuichi, 1989)

Bonobos are social animals and travel in groups of mixed company: males, females, and juvenile offspring. Typically, bonobos travel and feed groups of 3 to 6 individuals, but groups may have as many as 10. At Wamba (a research site where sugar cane fields that can accommodate many individuals are numerous and provisioning with sugar cane is also practiced), group size is much larger, and often reaches 30 individuals. Throughout their range, bonobos temporarily gather in larger groups around plentiful foods, but fission into smaller groups as they move on. The pattern is similar to that of the fission-fusion dynamic of P. troglodytes, with group size generally limited by availability of certain food items. (Horn, 1980; Kano, 1982)

Males have a loose dominance structure. Male bonobos stay in their natal group for life, whereas females leave during adolescence to join another group. A male bonobo’s rise in dominance is correlated with a mother’s strong presence in the group. Dominance manifests itself via threat displays, and is frequently associated with gaining access to food. Most threat displays are unidirectional (the ‘offender’ backs down without challenging). Afterward, reassurance behaviors minimize any lingering tension. Older female bonobos gain social status as their male offspring rise in dominance. (Furuichi, 1989; Ihobe, 1992b)

Although bonobos are generally knuckle-walkers, they walk bipedally on occasion. Further, they are agile in trees, both climbing and swinging or leaping between branches.

During rest periods, grooming is a common activity. It occurs most frequently between a male and female, though often between two females. It has been interpreted as not a greeting, courtship, or tension-relieving behavior, but rather as an ‘inter-individual affinity’ or group cohesion activity. (Kano, 1980)

A major focus of research on bonobos centers around their use sexual behaviors in non-reproductive contexts. These non-copulatory behaviors include female-female contact (genito-genito-rubbing, or GG rubbing), male-male contact (mounting and rump contact), and a long period of juvenile and adolescent copulation mimicry (albeit without intromission). A large amount of the research has been to document the frequency of each behavior between every pair of group members. These behaviors are observed in females particularly upon entering a new group after leaving their natal group, and at feeding locales where a large quantity of food is encountered. These sexual behaviors may be a way of negotiating and enforcing status differences within both females and males. (Badrian and Badrian, 1984; Furuichi, 1987; Furuichi, 1989; Ihobe, 1992b; Kano, 1980; Kano, 1982; Kano, 1992; Kano, 1996; Savage-Rumbaugh and Wilkerson, 1978; Thompson-Handler, Malenky, and Badrian, 1984; Uehara, 1988)

Home Range

Bonobo populations have been observed over ranges of between 14 and 29 square kilometers. However, these reflect observational data, rather than an attempt to map the home range size of any particular group. (Kano, 1982)

Bonobos communicate in a variety of ways. Females have a scream, but males bark, grunt, and pant-hoot. A bark may indicate alarm, whereas other vocalizations may indicate aggression, excitement, satisfaction, etc. The separate types of calls are used in multiple contexts, and cannot be thought of as "words".

In addition to this vocal communication, tactile communication is important. Social rank is communicated by GG rubbing, mounting, or rump contact. (See behavior section.) Other forms of tactile communication are seen between mothers and their offspring, and between rivals.

Visual communication also occurs. Bonobos often "peer" at another individual. This behavior indicates interest in the activity of the "peered at" individual. Peering may occur when oneother bonobo has a food item that is wanted, or it may be included in the courtship behavior of a male. (Kano, 1992)

Fruit comprises the largest portion of the diet of P. paniscus, although bonobos incorporate a wide variety of other food items into their diet. Plant parts consumed include fruit, nuts, stems, shoots, pith, leaves, roots, tubers and flowers. Mushrooms are also occasionally consumed. Invertebrates form a small proportion of the diet and include termites, grubs, and worms. On rare occasions, bonobos have been known to eat meat. They have been directly observed eating flying squirrels (Anomalurus sp.), duiker (Cephalophus dorsalis and Cephalophus nigrifrons), and bats (Eidolon sp.). (Badrian and Malenky, 1984; Horn, 1980; Kano and Mulavwa, 1984)

The only verified predators of bonobos are humans. Although the hunting of bonobos is illegal, poaching is still common. It has been speculated that leopards and pythons, known to prey on common chimpanzees, may also feed on bonobos. (Horn, 1980; Van Krunkelsven, 2001)

The quantity of fruit consumed by bonobos suggests that they may play a role in dispersal of the species eaten.

Bonobos may eat sugarcane that is being grown for profit. However, direct references to this being a problem for humans have not been encountered in the literature.

Bonobos, similar to common chimpanzees, carry many of the same diseases that can afflict humans, such as polio. (Van Krunkelsven, 2001)

Bonobos and their sister species, common chimpanzees, are the closest relatives to Homo sapiens. They are an invaluable source of information in studying human origins and diseases.

Bonobos are endearing to humans as 'charasmatic megafauna' and may be useful in encouraging conservation for habitat preservation.

Bonobos continue to be a source of bush meat for human consumption, and although hunting bonobos has been legally outlawed, poaching continues. (Van Krunkelsven, 2001)

Bonobos are an endangered species according to both IUCN and US Federal Endangered Species lists. The IUCN criteria project a 50% or greater reduction in their numbers within three generations, due to both exploitation and habitat destruction. Bonobos face “a very high risk of extinction in the wild in the near future” according to the IUCN Red List criteria. Civil war and its aftermath have hampered conservation efforts. Population estimates vary widely as conflict has limited the ability of researchers to work in the region. Estimates range from 5,000 to 17,000 individuals left. (Van Krunkelsven, 2001)