Mountain 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. 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.
George Schaller recorded that 10% of individuals around Kabara never made nests and argued that as ground nests serve no function, the drive to build them must have been inherited from an arboreal ancestor. Infants imitate the process from 15 months old though they sleep with their mother until they turn three.
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.
This was an adapted excerpt from the award-winning Gorilla Highlands Interactive eBook.