You’ll hear them before you see them; from somewhere deep in the forest, an excited hooting, just one voice at first, then several, rising in volume and tempo and pitch to a frenzied unified crescendo, before stopping abruptly or fading away.
Jane Goodall called it the ‘pant-hoot’ call, kind of bonding ritual that allows any Chimpanzees within earshot of each other to identify exactly who is round at any given moment, through the individuals’ unique vocal stylization.
To the human listener, this eruptive crescendo is one of the most spine chilling and exciting sounds of the rain-forest, and a strong indicator that visual contact with man’s closest genetic relative is imminent.
A Close Relative to Humans
It is, in large part, our close evolutionary kinship with Chimpanzees that makes these sociable black-coated apes of the forest so enduringly fascinating. Humans, Chimpanzees and bonobos (also known as pygmy Chimpanzees) share more than 98% of their genetic code, and the three species are far more closely related to each other than they are to any other living creature, even gorillas.
Superficial differences notwithstanding, the similarities between humans and Chimps are consistently striking, not only in the skeletal behavioural aspects. Baboons, for instance, are the only animals other than humans to copulate in the missionary position.
Where to find Chimps
Chimpanzees are essentially inhabitants of the western rainforest, but their range does extend into the extreme west of Tanzania, Rwanda and Uganda, which have a combined population of perhaps 7,000 individuals. These are concentrated in Tanzania’s Mahale and Gombe national parks, Rwanda’s Nyungwe forest, and about 20 Ugandan national parks and other reserves, most notably Budongo, Kibale , Semliki, Maramagambo and Bwindi. Although East Africa’s Chimps represent less than 3% of the global population, much of what is known about wild Chimpanzee society and behaviour stems from the region, in particular the ongoing research projects initiated in Gombe Stream and Mahale Mountain national parks back in the 1960s.
What Chimpanzees Eat
Prior to the 1960s, it was always assumed that Chimps were strict vegetarians. This notion was rocked when Jane Goodall, during her pioneering Chimpanzee study in Tanzania’s Gombe Stream. Witnessed them hunting down a red colobus monkey, something that has since been discovered to be common behaviour, particularly during the dry season when other food sources are depleted. Over subsequent years, an average of 20 kills has been recorded in Gombe annually, with red colobus the prey on more than half of these occasions, through young bushbuck, young bushing and even infant Chimps have also been victimized and eaten.
The normal modus operandi is for four or five adult Chimps to slowly encircle a colobus troop, then for another Chimp to act as a decoy, creating deliberate confusion in the hope that it will drive that monkeys into the trap, or cause a mother to drop her baby.
An interesting pattern that emerged from the parallel research projects in these two reserves, situated little more than 100km apart along the shore of Lake Tanganyika, is a variety of social and behavioural differences between their Chimp populations. Of the plant species common to both national parks, for instance, as many as 40% of those utilized as a food source by Chimps in the one reserve are not eaten by Chimps in the other.
In Gombe Stream, Chimps appear to regard the palmnut as something of a delicacy, but while the same plants grow profusely in Mahale, the Chimps there have yet to be recorded eating them. Likewise, the ‘termite-fishing’ behaviour first recorded by Jane Goodall at Gombe Stream, Chimps in the 1960s has a parallel in Mahale, where the Chimps are often seen ‘fishing’ for carpenter ants in the trees. But the Mahale Chimps have never been recorded fishing for termite, while the Gombe Chimps are not known to fish for carpenter ants.
Behavior & Reproduction
Unlike most other primates, Chimpanzees don’t live in troops, but instead form extended communities of up to 100 individuals, which roam the forest in small, socially mobile subgroups that often revolve around a few close family members such as brothers or a mother and daughter. Male Chimps normally spend their entire life within the community into which they were born, whereas females are likely to migrate into a neighbouring community at some point after reaching adolescence. A highly ranking male will occasionally attempt to monopolize a female in oestrus, but the more normal state of sexual affairs I Chimp society is non-hierarchical promiscuity.
A young female in aestrus will generally mate with any male that takes her fancy, while older females tend to form close bonds with a few specific males, sometimes allowing themselves to be monopolized by a favoured suitor for a period, but never pairing off exclusively in the long term.
Within each community, one alpha male is normally recognized – through coalitions between two males, often a dominant and a submissive sibling – have often been recorded. The role of the alpha male, not fully understood, is evidently quite benevolent male’s-chairman of the board rather than crusty tyrant.
This is probably influenced by the alpha relatively limited reproductive advantages over his potential rivals, most of whom he will have known for his entire life. Other males in the community are generally supportive rather than competitive towards the alpha male, except for when a rival consciously contests the alpha position, which is far from being an everyday occurrence. One male in Tanzania’s Mahale Mountains maintained an alpha status within his community for more than 15 years between 1979 and 1995!
Although Chimp communities appear by and large to be stable and peaceful entities, intensive warfare has been known to erupt within the habituated communities of Mabale and Gombe. In Mahale, one of the two communities originally habituated by researchers in the 1967 had exterminated the other by 1982. A similar thing happened in Gombe Stream in the 1970s, when the Kasekela community, originally habituated by Goodall, divided into two discrete communities. The Kasekela and breakaway Kahama community coexisted alongside each other for some years. Then in 1974, Goodall returned to Gombe Stream after a break to discover that the Kasekela males one by one, and tearing into them until they were dead or terminally wounded. By 1977, the Kahama community had vanished entirely.
Mahale’s Chimps routinely groom each other with one hand while holding their other hands together above their heads – once again, behaviour that has never been noted at Gombe. More than any structural similarity, more even than any single quirk of Chimpanzee behaviour, it’s such striking cultural differences – the influence of nurture over nature if you like – that bring home our close genetic kinship with Chimpanzees.