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)
Bonobos are polygynandrous. Females may be approached by and copulate with, any male in the group except their sons. However, the mating system may be confused by the use of sexual activity in these animals as part of social bond formation. (Kano, 1992)
Basic life history traits of bonobos are under-researched. Some of the seminal studies of this species have noted that “bonobos have not yet been studied long enough to provide data on age at sexual maturity or birth interval” (Nishida and Hiraiwa-Hasegawa, 1987), the most frequently researched “Wamba and Lomako study populations lack long-term demographic data” (Thompson-Handler et al., 1984), and “information on the demography of wild bonobos is very limited compared to that for chimpanzees” (Furuichi et al., 1998).
Female bonobos undergo estrus, marked by distinctive swelling of the perineal tissue lasting 10 to 20 days. Matings are concentrated during the time of maximal swelling. Breeding occurs throughout the year. Postpartum amenorrhea lasts less than one year in bonobos. A female may resume external signs of estrus (i.e. swelling) within a year of giving birth. At this point, copulation may resume, although these copulations do not lead to conception, indicating that the female is probably not fertile. During this period, she continues to lactate until her offspring is weaned at around 4 years. The average interbirth interval is 4.6 years (4.8 if one only includes live births). Therefore, lactation may suppress ovulation, but not the outward signs of estrus. As no study has lasted longer than a bonobo lifespan, total number of offspring per female is unknown. However, at Wamba, many adult females had four offspring during the 20 year study length. (Dahl, 1986; Furuichi, et al., 1998; Furuichi, 1987; Savage-Rumbaugh and Wilkerson, 1978)
Adult female bonobos have an estrus period that is marked externally by physical changes in their genitalia. During this time, males of the group approache the female, displaying their erect penises. Females are generally receptive, and will move toward a male to allow copulation. There is no clear pattern of mate choice: females are courted by many males of the group during estrus, with the exception of their sons. Because of this, paternity is generally unknown to both partners. (Kano, 1992)
Information is limited on parental investment. However, bonobos are highly social mammals and live around 15 years before achieving full adult status. During this time, the mother provides most of the parenting, although the males may contribute indirectly (i.e. in alerting the group of danger, sharing food, and possibly helping to protect young).
Bonobo babies are born relatively helpless. They are dependent on mothers’ milk and cling to their mother for several months. Parental care is provided by the mother, as paternity is generally unclear. Weaning is a gradual process, and is usually commenced by the time the offspring is 4 years of age. Throughout the weaning process, mothers generally have their offspring feed by their side, allowing them to observe the feeding process and food choice, rather than providing them with food directly. Weaning may be enforced by a mother’s refusal to allow a juvenile into her nest, thereby encouraging it to build a nest of its own.
As adults, male bonobos typically remain in their natal social group, so they have contact with their mothers throughout her remaining years. Female offspring leave their natal group during late adolescence, so they do not maintain contact with their mothers in adulthood. (Fruth and Hohmann, 1993; Horn, 1980; Kano, 1992)
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, 1992)
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, 1992; Kano, 1980; Kano, 1982; Kano, 1992; Kano, 1996; Savage-Rumbaugh and Wilkerson, 1978; Thompson-Handler, et al., 1984; Uehara, 1988)
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 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 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 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)
Nancy Shefferly (editor), Animal Diversity Web.
Anna Williams (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
uses sound to communicate
young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.
Referring to an animal that lives in trees; tree-climbing.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
uses smells or other chemicals to communicate
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.
union of egg and spermatozoan
A substance that provides both nutrients and energy to a living thing.
forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.
an animal that mainly eats fruit
An animal that eats mainly plants or parts of plants.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
marshes are wetland areas often dominated by grasses and reeds.
having the capacity to move from one place to another.
the area in which the animal is naturally found, the region in which it is endemic.
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.
remains in the same area
reproduction that includes combining the genetic contribution of two individuals, a male and a female
associates with others of its species; forms social groups.
uses touch to communicate
Living on the ground.
the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.
uses sight to communicate
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
breeding takes place throughout the year
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