Bonobo

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. 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.

## Range and Habitat

Wild bonobos can only be found in forests south of the Congo River in the Democratic Republic of Congo. Sometimes known as the pygmy chimpanzee, bonobos weren’t recognized as a separate species until 1929. As the last great ape to be scientifically described, much remains unknown about the bonobo—including the extent of its geographic range. Efforts to survey the species over the past two decades have been hampered by the remote nature of its habitat, the patchiness of their distribution and years of civil unrest within the DRC. 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. 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. 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).

## Ecology

The population density of bonobos is hard to estimate, but some studies have put it at 0.4 individuals per km² (.249 per mi²). Even in the most densely populated areas, these apes have a patchy distribution.

### **Diet**

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.

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 infraspecific feeding competition and heightened sociality, especially between females.

### **Differences from Chimpanzees**

Bonobos and chimpanzees look very similar and both share 98.7% of their DNA with humans—making the two species our closest living relatives. Bonobos are usually a bit smaller, leaner and darker than chimpanzees. Their society is also different—bonobo groups tend to be more peaceful and are led by females. They also maintain relationships and settle conflicts through sex. However, bonobo life isn’t entirely violence free; if two groups of bonobos come together, they may engage in serious fighting.

## Poaching

Humans hunt bonobos to eat them, trade them as bushmeat, keep them as pets and for use in traditional medicine. Specific bonobo body parts are believed to enhance sexual vigor or strength. The number of bonobos lost to poaching each year is not known, but the number of bonobo charms available in parts of the Democratic Republic of Congo suggests that poaching may be common.

### **Habitat Loss**

Only part of the bonobo’s range lies in protected areas. A growing and moving human population, combined with slash-and-burn agriculture and commercial logging, leaves bonobos outside parks at risk of losing their homes.