Since the discovery that humans share 98.3% of our DNA with gorillas, making them our closest relatives after chimpanzees and bonobos, more scientific, conservation and tourism traffic has been directed towards these massive rain forest inhabitants. We now know that there are two species of gorilla – the eastern gorilla (Gorilla beringei) and western gorilla (G. gorilla).
Each of these is further divided into two subspecies:
Both these sub species live in central Africa, separated by a vast swathe of rainforest, and are both listed as Critically Endangered on the IUCN Red List.
The western lowland gorilla is the most numerous of the four subspecies, with population estimates often cited at 100,000-200,000. However, due to their dense, remote habitat, no one knows for sure how many exist. The least numerous is the cross river gorilla, which is confined to scattered areas of forest in Nigeria and Cameroon, and is thought to number no more than 300 individuals.
Recent surveys in the Virunga Massif estimate that the mountain gorilla population now stands at 1,004.
However, our interest today in the relationship between the two major gorilla species, the lowland gorilla in central Africa and the mountain gorilla in the Virunga massif in East Africa.
These two subspecies of gorillas are often lumped into one. You’ll find that they have distinct differences; the mountain gorilla is larger, with longer hair and shorter arms than their lowland gorilla cousins and can only survive in high altitudes of about 2,200–4,300 metres (7,200–14,100 ft). Lowland gorillas are much more likely to be seen in the trees, and prefer a more heavily forested, flatter habitat than the mountain gorilla.
Mountain Gorillas (Gorilla beringei graueri), or Eastern gorilla, is found in two places, that is, in the Virunga volcanoes mountains that separate the Democratic Republic of Congo from Rwanda and Uganda (seen in Volcanoes National Park Rwanda, Virunga National Park Congo and Mgahinga National Park Uganda) and the other half of the 1000 of them can be found in Bwindi Forest National Park.
Western or lowland gorillas inhabit the forests of equatorial Africa from the western lowlands near the Cameroon coast through the Central African Republic, Equatorial Guinea, Gabon, Nigeria, Republic of Congo, Angola, and possibly the Democratic Republic of Congo.
As their names suggest, the two subspecies of gorilla have very different habitats. The lowland gorillas make their homes in the thick rain forests on the Atlantic Coast of Africa. They have a relatively small area that they still live in in the wild, including untouched wilderness in Congo, Equatorial Guinea, Central African Republic, and Cameroon.
The mountain gorilla is found at much higher altitudes and much farther inland, surviving in a pocket of wilderness in Rwanda, Uganda, and the Democratic Republic of Congo. Most of their native habitats are the rocky slopes of once-active volcanoes, although they are known to venture into the high, alpine regions of the mountain ranges where they can face freezing temperatures.
Both subspecies live in family groups called “troops.” Large troops with as many as 30 individuals have been seen, but the usual makeup of these families is quite a bit smaller. A gorilla troop usually consists of one dominant male, a handful of his females, and their immature offspring. Adult male children will split off from their family unit to travel alone; around the age of 15, males will begin collecting their own harem of females and start their own family group. Between leaving their parents and collecting females of their own, immature lowland males will occasionally form their own troop, sometimes attached to a parent group.
There is some difference in the physical features between the two, although it can be hard to distinguish at a glance. Both have very long arms—their arm span is longer than they are tall—but mountain gorillas typically have shorter arms than their lowland cousin. They also have a larger nose and jaw, and larger teeth.
When stressed or upset, male mountain gorillas emit a strong odor from glands under their arms. Studies of lowland gorillas have so far shown that scent communication doesn’t play as large a role in their culture.
Gorillas are highly intelligent. They don’t use tools as much as chimpanzees do, but wild gorillas have been seen using sticks to gauge water depth, bamboo as ladders to help infants climb, and recently gorillas have been seen for the first time using sticks to eat ants without being stung.
Another sign of intelligence is the gorilla’s impressive communication abilities, and they’ve been recorded making some 25 different sounds.
Gorillas build nests in which to sleep, both on the ground and in trees, made of leaves and branches. Counting abandoned nests is an effective way for scientists to estimate population size.