put this in perspective, animals have existed on Earth for over
600 million years, mammals for at least 200 million; the first
known primate about 70 million years, the first hominids at
least 6 million years, the first men (Homo sapiens) 300,000
years and modern man (Homo s. Sapiens) only about 50,000 years.
The modern apes are all essentially vegetarian: gorillas are
predominantly leaf-eaters; only the chimpanzees include a
significant proportion of meat in their diet, sometimes hunting
cooperatively for colobus monkeys or other medium-sized mammals
and they will even share food. Their hunting behaviour, as
well as their use of tools such as stones for cracking nuts
and twigs for extracting termites, has attracted attention
from field researchers for its relevance to the behaviour
of early humans.
There is only one species of gorilla, divided into three subspecies:
Gorilla gorilla gorilla (Western Lowland Gorilla); Gorilla
gorilla graueri (Eastern Lowland Gorilla) and (Mountain gorilla).
Until recently, the Eastern Lowland Gorilla was considered
to be a form of Mountain Gorilla. Mountain gorillas live in
two isolated populations, one in the Virunga volcanoes which
sprawl across the borders of Rwanda, Zaire and Uganda in Central
Africa, and the other in the Bwindi National ("Impenetrable")
forest in Uganda. There is some speculation that this Bwindi
population may be yet another subspecies.
Mountain gorillas are physically distinct from Lowland Gorillas;
they are larger, have longer, thicker fur and a slightly different
nose shape among other skeletal differences. They are the
largest living primates, an adult male weighing up to 180
kilograms (400 pounds), with an arm span of about two metres
(seven feet). Adult females weigh about half as much as males.
When he reaches maturity, a male develops silvery grey hairs
on his back and is called a "silverback" - in a
group of gorillas, a silverback is usually the sole dominant
member and living with him are several females, infants, juveniles
and young adults.
Gorillas are diurnal, sleeping each night in a fresh nest
built from leaves and branches. They are nomadic within their
range and so, usually, end up in a new location each night.
Normally they become active around dawn but if it is a cold
overcast morning they may lie in for a while; although close
to the equator, it can be very cold where the mountain gorillas
live in the Virunga volcanoes at around 3,000 metres or more.
On occasion they even venture into the sub-alpine zone in
search of different foodplants such as the pith of the giant
Senecio and where, at an altitude of over 3,500 metres there
can be frost in the mornings.
The mountain gorillas' day is a routine of alternating periods
of feeding and resting. They are almost exclusively vegetarian:
bamboo, nettles and Gallium being some of their favourite
foods. They will occasionally eat grubs, which they find in
rotten wood, and even safari ants, scooping them up in huge
handfuls to stuff into the mouth until the bites of the ants
become overpowering and drive the gorillas away. It is the
silverback leader who decides when the activities of the day
begin and finish; when he moves, everyone moves; when he stops
to rest, everyone stops. He is the emotional centre, the magnet
of the group. His power not only derives from his size but
the fact that he is the protector and everybody follows him.
In a typical rest period, the silverback dozes surrounded
by the rest of the group while the juveniles and infants play.
Rest periods present good opportunities for social bonding,
not only in play behaviour but also in grooming one another.
The younger members of the group spend a good proportion of
their time climbing, and swinging from branches, but adult
gorillas are too heavy, only occasionally hauling their pear-shaped
bodies up into a tree to reach an irresistible item of food
spotted from the ground. On the ground, gorillas usually walk
on all fours, supporting most of their weight on the feet
and walking on the large front knuckles.
Being very social, communication is important manifesting
itself in a variety of grunts, howls, hoots and barks. There
are nearly twenty different vocalisations, each one with its
own particular meaning. Gorillas also communicate by beating
on their chests, or on the ground. For the silverback male,
chestbeating is a show of power, designed to intimidate, but
even the infants beat their chests as a kind of displacement
activity during play, perhaps in mimic of their elders.
Mountain gorillas may live for thirty-five to forty years,
reaching sexual maturity between the ages of eight and eleven.
Full maturity for a male is a long haul for, although he begins
to develop the "silver back" at the age of twelve
or thirteen, he usually leaves his parental group at that
time to wander alone, or in the company of other males, for
a few years before managing to attract females from other
groups to join him, thus forming his own family. It is a logical
evolutionary process that sorts out the strong from the weak.
When a female leaves her group to join another male, the new
silverback will most likely kill an accompanying infant, a
seemingly cruel and callous act to us but one which brings
the female into oestrus for him to mate and thus ensure his
own blood line. In the gorillas' social structure where the
breeding in any one group is almost exclusively by a single
silverback male, periodic movement of females between groups
is essential to ensure genetic variety and to prevent inbreeding,
a peril in small populations