Western Lowland Gorilla
|Geographical Range||Western equatorial Africa|
|Scientific Name||Gorilla gorilla gorilla|
|Conservation Status||Critically endangered|
What’s one of the first things you notice about gorillas? Probably their great size. These are the largest living primates (a group that includes monkeys, apes, and humans). A fully-grown male gorilla weighs up to 400 pounds and measures about 5 ½ feet tall. Females are just a bit shorter (about five feet) but weigh considerably less (about 200 pounds).
Despite their formidable size, gorillas are gentle animals. In fact, thousands of tourists in Africa every year walk safely within a few yards of wild gorillas. These apes are aggressive only when fighting over females or protecting their family from predators and hunters.
Not Just a Pretty Face
To us humans, a gorilla may seem (mistakenly) fearsome not only because of its great size, but also because of its powerful-looking head. The top of the head has a ridge running down the middle (more pronounced in males). The ridge serves an important purpose: it’s the attachment point for the jaw muscles, which have to be big in order to process the large amounts of food gorillas need to sustain their huge bulk. Similarly, gorillas’ teeth are large in order to chew all that food more efficiently. And males have extra-large canine teeth, capable of inflicting serious wounds on rival males or predators.
Gorillas’ face, hands, and feet are bare, but the rest of their body is covered with hair. The shade of hair varies, depending on the type of gorilla. There are two main species (types) of gorilla – western and eastern – and each of those has two subspecies. The western lowland gorilla (the subspecies we have at the Saint Louis Zoo) tends to be brownish-gray in color, while the eastern gorilla is black. In all types of gorilla, adult males stand out in a crowd: their backs are covered with silvery-white hair. (It’s no wonder we call them “silverbacks.”)
Like all apes, gorillas’ arms are longer than their legs – a handy feature that allows them to walk on all fours. Gorillas, like chimpanzees, are so-called “knuckle walkers,” meaning they walk on the knuckles of their fore limbs and the soles of their hind limbs. Though knuckle walking is their main mode of travel, gorillas are able stand on two legs for short periods of time (such as during a chest-beating display – more on that later!).
Something Fruity, Please
What’s on the menu for gorillas? Western lowland gorillas prefer fruit whenever it’s in season, and they eat a lot more fruit than eastern gorillas (because there are more fruit trees in the west). When fruit isn’t available, western lowland gorillas snack on other plant parts, including seeds, leaves, and stems. Occasionally they eat animals (mostly termites – yum!).
Given their diet, it’s no surprise that western lowland gorillas spend a lot of their time in and around trees, especially fruit trees. Even large males can sometimes be found up in the trees, but they have to be careful to stay near the main trunk or on large branches that will support their weight. Younger, lighter gorillas clamber around in the trees more freely, and can even swing from branch to branch (like chimpanzees).
Bringing Up Baby (Gorillas, That Is)
Gorillas breed at any time of year. Among western lowland gorillas, a family group usually contains just one adult male, and the females in that group breed with him. The length of pregnancy (or gestation period) is about 36 to 37 weeks – about two weeks shorter than in humans.
Gorillas generally give birth to just one baby at a time (twins being very rare). Given the large size of adult gorillas, it’s amazing to see how small a newborn is – just four or five pounds (considerably less than most human babies!). The little one holds tightly to mom’s hair and hitches a ride with her for the first three to four months of life. Mom will continue to nurse her baby for at least three years.
Young female gorillas generally don't breed until they’re at least ten years old. In the course of her life, a female will have a new baby about every four years. But since only half of all gorilla babies survive to adulthood, a female usually has just two or three surviving young during her lifetime.
Compared to females, males mature a little later, and very few start to breed before 15 to 20 years of age (because females prefer older males).
Most gorillas live in family groups, which generally include a silverback (adult male), multiple females, and their offspring. Among western lowland gorillas, family groups are fairly small – usually about five individuals, and rarely more than ten. This group size is smaller than among eastern gorillas, and is probably due to the particular nature of the western gorillas’ diet: they eat a lot of fruit, and since fruit trees can be widely scattered, a given area supports a smaller number of individuals.
The family group tends to be very stable: the silverback retains his leadership for years, and the females in his harem may stay with him for life (if they do well in his group). The adult females in the harem are unrelated: when young, they left the groups in which they were born to hook up with a nearby silverback. (About 75% of females emigrate out of their birth group). The females choose their silverback based on the quality of his habitat as well as his leadership ability.
Like females, many males (about 50%) leave the group of their birth when they hit puberty. At first, they travel alone or with other males in so-called bachelor groups. This may last for years, until the males acquire females from other groups and start their own harems.
Two silverbacks (the resident harem-leader and a lone male) may challenge each other for leadership of the family group. When this happens, the silverbacks often perform elaborate displays of strength, which may include chest-beating, hooting and throwing vegetation. Occasionally the displays lead to a fight to the death (usually of the lone male).
But fights are rare. For the most part, gorillas live in peace – both within a group and between groups. A group spends most of the daylight hours searching for and eating food and resting. At night, they often sleep in nests which they make quickly (in less than five minutes) and use only once.
Gorillas In Danger
All types of gorillas are in serious danger of extinction in the wild. Western gorillas number only about 110,000 – most of them the western lowland subspecies, plus a few hundred of the other western subspecies, the Cross River gorilla. Eastern gorillas are even more rare: one subspecies, the eastern lowland gorilla, numbers only about 10,000, while the mountain gorilla subspecies numbers just a few hundred. That means there are fewer than 125,000 wild gorillas total.
What’s happening to gorillas? Logging is the root of the problem. First of all and most obviously, logging destroys gorillas’ habitat (as does the expansion of agriculture and human settlements). But logging leads to other problems as well. Loggers build roads that provide an easy route for the spread of lethal diseases like ebola. Roads also make it easy for hunters to come into the forest and poach gorillas and other animals. While some gorillas continue to be hunted for body parts (to make gorilla-hand ashtrays, for instance), more and more gorillas are being killed for food. This bushmeat trade, as it’s called, affects other animals as well (including chimpanzees and Sumatran orangutans). These animals are being killed for their meat at a rate faster than they can reproduce. In some cases, hunters are poor people who need the protein to survive. But more and more, the carcasses are being sold to cities, where bushmeat is bought as a “gourmet” food.
Conservation groups are working to solve the bushmeat crisis before it’s too late for gorillas and other endangered animals. To learn more about what’s being done to help gorillas and other bushmeat victims, learn about the work of the Bushmeat Crisis Task Force .
What can you do to help gorillas? You can help protect their habitat. Make sure that you, your family, and friends choose wisely when buying wood products. Don’t buy items made from trees that were logged from gorillas’ habitat. Also, tell everyone you know to recycle their cell phones. Cell phones contain the mineral coltan, much of which is mined by destroying gorillas’ habitat. You can make a difference!
- As discussed above, recent genetic studies have shown that there are two species of gorilla, each with two subspecies. Before these studies came out, scholars believed all gorillas belonged to a single species, divided into three subspecies: western lowland, eastern lowland, and mountain. Most scientists now accept the revised scheme, which shows a genetic separation between the eastern and western types.
- The western lowland gorilla is not the gorilla featured in the book and movie Gorillas in the Mist. That’s the mountain gorilla (one of the subspecies of eastern gorilla).
- Perhaps surprisingly, the habits of western lowland gorillas are less well known that those of eastern gorillas, even though the western type is more numerous. That’s because western lowland gorillas live in such dense jungle that they’re hard to observe.
- Western lowland gorillas eat parts of at least 97 plant species.
- Gorillas can live for 50 years or more, both in the wild and in captivity, though such a long lifespan is rare.