TAXONOMY & DESCRIPTION
The robust or common chimpanzee is a large ape belonging to the order of primates, and the family hominidae, which also includes the gorilla, orang-utan, and bonobo. Chimpanzee males are smaller than the male orang-utan or gorilla. The females have similar body measurements to female orang-utan. The average male head-body length measurement is 850mm and weight range is between 40-60kgs for males and 33-46kg for females.
The current consensus is that there are two species of chimpanzees; Pan troglodytes and Pan paniscus. There are four subspecies of the robust or common chimpanzee; Pan troglodytes verus; Pan troglodytes vellerosus; Pan troglodytes troglodytes and Pan troglodytes schweinfurthii, and at this stage no subspecies is recognised for the gracile chimpanzee, better known as the Bonobo or Pygmy chimpanzee Pan paniscus.
Chimpanzee pelage is generally black, though individuals with brown pelage have been observed, which can go grey with some individuals upon maturity. Skin colouration varies with age. Infants are often born with pale skin, which gradually darkens as they become adults. Generally as the chimpanzee matures the skin becomes black though sometimes individuals retain a pale skin and some will have freckles.
DISTRIBUTION & ABUNDANCE
The historical chimpanzee range was at least 25 countries throughout Equatorial Africa. Today, chimpanzees occur in 22 countries from 13oN to 7oS latitude. The present range covers an area of approximately 2,342,000kmsq, but distribution and numbers are poorly known in most areas. There is a vast difference in the geographic and known ranges of the four sub species of chimpanzees. While data relating to the distribution and approximate number of chimpanzees in some countries exist, many populations have not been surveyed or have only had isolated surveys in some forest blocks as they are of interest to particular conservation organisations.
While there has been an effort made in the past five years to carry out surveys in many countries, there have been very few countrywide censuses where forests have been extensively surveyed.
The West African sub species (P. t.verus) occurs in 10 countries in West Africa. The current known populations are fragmented and declining in numbers. Historically, P. t.verus were believed to have occurred in 12 countries. The geographical ranged was 631,000kmsq with an estimated population range from 21,000 to 55,000.
The recent identification of a new subspecies P.t.vellerosus includes the population of chimpanzees straddling the northern border of Cameroon and the Southern border of Nigeria between the Niger River and Sanaga Rivers (into this subspecies). They have a relatively limited range of 142,000kmsq. The estimated number for this subspecies is between 5,000 and 8,000 individuals.
The range of central African subspecies (P .t. troglodytes) range extends across seven countries from Cameroon in the north to the Congo River in Peoples Republic of Congo (PRC)). The largest population of this subspecies is found in Cameroon and Gabon, while substantial population exist in PRC. Smaller populations are present in Equatorial Guinea, The Central African Republic (CAR), northern Angola and the extreme west of Democratic Republic of Congo (DRC). The known geographic range is approximately 695,000kmsq. The central African chimpanzee population is estimated to be between 70,000-116,000 individuals. This subspecies is found in some of the most undisturbed habitat remaining. The eastern chimpanzee (P.t.schweinfurthi) occurs in seven countries with a geographic range of 874,00kmsq.
LOCOMOTION
Chimpanzees use various methods of locomotion. They are both terrestrial and arboreal. Brachiation, climbing, bipedalism and quadrupredal knuckle-walking can all be observed in chimpanzees. They will feed and rest on both the ground and in the trees, although generally they will travel long distances on the ground. This habit of travelling on the ground has made chimpanzees and gorillas vulnerable to snares set by hunters.
NEST BUILDING
Chimpanzees build nests to sleep in, normally building one nest each night, unless they reuse a nest from a previous night or occupant. Chimpanzees build arboreal nests and use a foundation of solid side branches or forks, bending, breaking and inter-weaving the branches cross-wise, generally constructing the nest in a circular fashion. Chimpanzees will occasionally build day nests as well, building nests on the ground. This nest building habit has proven to be very useful to researchers who have found it to be the most practical and accurate way of estimating population size of unhabituated chimpanzees.
MOTHER-INFANT BEHAVIOUR
Mothers care for their offspring for an extended period of time and infants are totally dependant on their mothers for 6-7 years. Some still require their mothers support emotionally as they mature and become independent. Due to this close physical and emotional relationship between mother and infant, the removal of an infant from the wild to supply zoos, laboratories and animal dealers can only be carried out by killing the mother. This has contributed to a significant loss of females and infants from in-situ populations.
PLAY
Infants and juvenile spend at least 5% of their time playing each day. Adults sometimes play with infants, and even with each other, but this is less common. Play is usually accompanied by a play face, and when play becomes boisterous, chimps laugh. Play includes tickling, wrestling and chasing and sometimes incorporates objects such as leafy twigs, sticks, stones and large fruit. Sometimes infants will play on their own.
SLEEP
Each evening, chimpanzees construct a fresh “sleeping nest” in the trees where they will curl up and sleep. These bowl-shaped nests are made out of leaves and other plant material. Nests are only shared by a mother and her nursing offspring.