Contrary to old myths about bloodthirsty gorillas hunting humans, mountain gorillas are peaceful vegetarians.
What Do Mountain Gorillas Eat?
They are herbivores, eating up to 140 different types of fruit, herbs, stems and roots. Like other primates they sometimes munch on ants and termites and have been seen to enjoy a communal meal off a favourite rotting log. They are not users of tools; their main manipulation of vegetation is to avoid being stung.
Most of their favoured food is found in the lush secondary growth of forest clearings and disturbed sites. Their favourite meal is ripe fruit — they will travel some distance for it and spend a substantial amount of their feeding time feasting on fruits. Otherwise, given that edible plants are all around them, their movement from one site to another appears to be random. Their diet depends on altitude, habitat and seasonal cycles.
They tend to be conservative, only eating what they know but refusing what gorillas elsewhere relish. However they can be trained to consume anything digestible in captivity, even meat. One district commissioner had a young gorilla that learnt how to catch mice, skin and eat them.
Their powerful jaw muscles and long canines allow them to crush hard plants like bamboo. They have a single stomach and long intestine, like humans, and must eat a lot. An adult male consumes 20 kg / 44 lb a day, which is why their stomachs are mostly bloated and they are renowned for their flatulence. They have a specialised digestive system, capable of detoxifying harmful compounds and have less need of plant medicines compared to chimpanzees and humans.
Contact with farmers has led them to discover the succulent banana that grows freely by the forests. They don’t eat the fruit. The stem core is what they enjoy and this spells disaster for farmers who see their crops ruined. They have also developed a taste for eucalyptus but don’t cause as much damage. Since gorillas have been habituated, they don’t fear humans as much and have realised that they can get away with raiding. Some groups are active a lot closer to human settlements than before.
And After a Long Day of Eating …
Gorilla nests are easily and quickly made; five minutes or less. On the ground it may be some piles of vegetation casually placed in a circle around the body; there is no manipulation of the materials. Tree nests are built where there are forks and horizontal branches for support; surrounding branches and vegetation add extra support and comfort.
It is unknown if nest building is inborn or a learned activity; it appears that the impulse is genetic and the techniques are learnt. Infants imitate the process from 15 months old though they sleep with their mother until they turn three. All gorillas build nests but the location varies. Where trees are strong, up to 50% of nests are arboreal while in the bushes of higher altitudes all nests are on the ground.
The techniques used by gorillas and chimpanzees are almost exactly the same. Nests are always abandoned after one night; a hygienic practice given that they defecate in there. Deserted nests are extremely valuable for gorilla researchers and doctors. By counting nests they estimate gorilla numbers, while hair samples and faeces can be analysed to establish their health.
featured image by Marcus Westberg; silverback photo by Jiro Ose