Western lowland gorillas are the largest of the primates and are critically endangered and are the smallest of the four sub-species. The males, on average, weigh approximately 135 - 220 kg (297 - 485 pounds) and the females weigh about half of that, around 70 - 90 kg (154 - 198 pounds). The male is very stocky and powerful in the body, with wide shoulders and chest. The females are much smaller and slimmer. The colour of the coat varies considerably, ranging from black, silver and shades of red. Black is the most common. Gorilla skin is also black. As a male gorilla reaches physical maturity (between 12 and 15 years of age), he develops his silvery grey colouration giving them the name of silverback.
Their habitat is primary and secondary forests, and lowland swamps and they are found in Cameroon, Central African Republic (CAR), mainland Equatorial Guinea (Rio Muni), Gabon, Nigeria, Republic of Congo (RoC), Cabinda (Angola), and possibly in the Democratic Republic of Congo (DRC). The core population had, until recently, an almost continuous distribution in suitable habitat from southern CAR to the Congo River and west to the coast. Small outlying populations remain on the Nigeria-Cameroon border at the headwaters of the Cross River and in the Ebo/Ndokbou forest in Cameroon, just north of the lower Sanaga River. The species may also persist in the Maiombe region of Democratic Republic of Congo contiguous with Cabinda.There has been a drastic decline in wild populations of gorillas worldwide due to hunting, disease and habitat loss. Experts estimate a more than 80% decline in their population, and we need to act now to prevent the risk of their extinction.
They are herbivores feeding mainly on juicy plant stems, vines and leaves. Bark, roots and fruits are also taken, the choice parts being selected, the remainder discarded. The bulk of the Zoo Diet consists of a wide variety of vegetables, supplemented with other food items such as leaf eater chow, tofu, soft bill gel, muffins, seeds, nuts and browse.
Females mature sexually, and are fully grown, around eight to ten years of age. Males are sexually mature at about 10 years of age and fully grown at 12 - 15 years. Females begin breeding as soon as they are sexually mature, but male gorillas need to physically mature so they can attain silverback status and lead a group of gorillas. Typically one dominant male within a gorilla troop mates with the females in that group. The dominant male, because of his perceived superior fighting ability, is preferred by the females as he will be better able to protect them and their offspring. This usually occurs between the ages of 15 and 20 years. In male apes, including humans, potency (the ability to sire offspring) is continuous until it is lost through senescence. Female gorillas have a menstrual cycle similar to that in humans, the average length being 30 - 31 days.
The average gestation period is 265 days or 8.5/9 months. A single young is born weighing approximately two kg (almost 4.5 pounds). The baby gorilla is completely dependent on its mom for food and protection. At birth they are strong enough to cling to their mother's hair. Mom will provide support with one hand when required. When on the move, she cradles the infant to her breast with one hand. It begins to eat vegetable matter at about six months of age, but nursing continues up to four years of age. By one month, the infant clings to it's mom unaided; by four months it rides on it's mom's back and by eight months it can climb and is very active.
Young gorillas are incredibly playful. Juveniles climb more frequently and with greater ease than the adults. Very often other females will play the role of "aunt" to a baby and participate in its care, playing with it and carrying it around. Gorillas live in fairly stable groups of five or six individuals. Groups usually consist of only one adult male with a few females and their young.
Gorillas are quiet most of the time, and they enjoy dozing and sunbathing in the mid-morning between bouts of feeding. Postures, gestures, facial expressions, and vocalizations are all used in communication within the group. Gorillas vocalize a great deal from the throat creating roars, growls, barks, grunts, purrs, croaks, hoots, squeaks, and screeches. Only one or two sounds carry far enough to reach other groups. They can very effectively warn each other of impending danger and intimidate intruders. The hooting sound is usually the prelude to the climax of their emotional expression - the drumming display. Flat or slightly cupped hands are beat in rapid alternation upon the chest, abdomen, hips, tree trunks, on the ground, or on anything that is handy. Drumming sounds the alarm in case of danger, threatens the invader, but it may also be done in play. This display includes rising on its legs, throwing vegetation in the air, leg kicking, running sideways, slapping and tearing nearby vegetation, and thumping the ground. Many variations occur, and some acts may occur alone. Aggressive charges rarely result in serious physical combat. The gorilla avoids conflict until extremely hard pressed, with the dominant male always acting in defense of his group.
As is the case with many species, humans are the primary threat to the survival of gorillas. Gorillas are widely hunted for "bushmeat" and the young are collected for sale to the pet trade, a practice that is now illegal. Habitat loss also significantly jeopardizes gorilla populations. The main reasons for habitat loss are mining for coltan (which is used in cell phones and other electronics), logging for timber and fuel wood, and agricultural expansion. Civil wars occurring in gorilla habitat are also a serious threat. Outbreaks of disease, in particular the Ebola virus are contributing factors to declining gorilla populations. Also, young gorillas are susceptible to predation by leopards.