The western lowland gorilla (Gorilla gorilla gorilla) is one of two critically endangered subspecies of the western gorilla (Gorilla gorilla) that lives in montane, primary and secondary forest and lowland swampland in central Africa in Angola (Cabinda Province), Cameroon, Central African Republic, Republic of the Congo, Democratic Republic of the Congo, Equatorial Guinea and Gabon. It is the nominate subspecies of the western gorilla, and the smallest of the four gorilla subspecies. The western lowland gorilla is the only subspecies kept in zoos with the exception of Amahoro, a female eastern lowland gorilla at Antwerp Zoo, and a few mountain gorillas kept captive in the Democratic Republic of the Congo.
Description
The western lowland gorilla is the smallest subspecies of gorilla but still has exceptional size and strength. This species of gorillas exhibits pronounced sexual dimorphism. They possess no tails and have jet black skin along with coarse black hair that covers their entire body except for the face, ears, hands and feet. The hair on the back and rump of males takes on a grey coloration and is also lost as they get older. This coloration is the reason why older males are known as "silverbacks". Their hands are proportionately large with nails on all digits (similar to those of humans) and very large thumbs. They have short muzzles, prominent brow ridges, large nostrils and small eyes and ears. Other features are large muscles in the jaw region along with broad and strong teeth. Among these teeth are strong sets of frontal canines and large molars in the back of the mouth for grinding fruits and vegetables. A male standing erect can be up to 1.83 m (6 ft 0 in) tall and weigh up to 227 kg (500 lb). Males have an average weight of 140 kg (310 lb), females of 70 kg (150 lb). Males in captivity, however, are noted to be capable of reaching weights up to 275 kg (606 lb). Males stand upright at 1.67 m (5 ft 6 in), females at 1.5 m (4 ft 11 in). Zoo owner John Aspinall claimed a silverback gorilla in his prime has the physical strength of seven or eight Olympic weightlifters, but this claim is unverified. Western gorillas frequently stand upright, but walk in a hunched, quadrupedal fashion, with hands curled and knuckles touching the ground; as a result, their arm span is greater than their standing height.
Albinism
The only known albino gorilla – named Snowflake – was a wild-born western lowland gorilla originally from Equatorial Guinea. Snowflake, a male gorilla, was taken from the wild and brought to the Barcelona Zoo in 1966 at a very young age. He presented the typical traits and characteristics of albinism seen in humans, including white hair, pinkish skin, light colored eyes, reduced visual perception and photophobia, and was diagnosed with non-syndromic albinism. The genetic variant for Snowflake's albinism was identified by the scientists as a non-synonymous single nucleotide polymorphism located in a transmembrane region of SLC45A2. This transporter is also known to be involved in oculocutaneous albinism type 4 in humans. As it is a recessive allele, and his parents were an uncle and niece who were both carriers, this revealed the first evidence of inbreeding in western lowland gorillas.
Behavior
Social structure
Western lowland gorilla groups travel within a home range typically between 8 and 45 km2 (3 and 17 sq mi) in area. Gorillas do not display territorial behavior, and neighboring groups often overlap ranges. The group usually favours a certain area within the home range, but seems to follow a seasonal pattern depending upon the availability of ripening fruits and, at some sites, localised large open clearings (swamps and "bais"). Gorillas normally travel 3–5 km (1.9–3.1 mi) per day. Populations feeding on high-energy foods that vary spatially and seasonally tend to have greater day ranges than those feeding on lower-quality but more consistently available foods. Larger groups travel greater distances in order to obtain sufficient food. It is easier for males to travel alone and move between groups, as before reaching the age of sexual maturity, males leave their natal group and go through a "bachelor stage" that can last several years either in solitary or in a nonbreeding group. However, while both sexes leave their birth group, females are always part of a breeding group. Males like to settle with other male members of their family. Their breeding groups consist of one silverback male, three adult females and their offspring. The male gorilla has the role of the protector. Females tend to make bonds with other females in their natal group only, but form strong bonds with males. Males also aggressively compete for contact with females. The group of gorillas is led by one or more adult males. In cases where there is more than one silverback male in a group, they are most likely father and son. Groups containing only one male are believed to be the basic unit of the social group, gradually growing in size due to reproduction and new members migrating in. In the study done at Lope, gorillas harvest most of their food arboreally, but less than half of their night nests are built in trees. They are often found on the ground, and the group has up to 30 gorillas. Western lowland gorillas live in the smallest family groups of all gorillas, with an average of four to eight members in each. The leader (the silverback) organizes group activities, like eating, nesting and travelling in their home range. Those who challenge this alpha male are apt to be cowed by impressive shows of physical power. He may stand upright, throw things, make aggressive charges, and pound his huge chest with open or cupped hands while barking out powerful hoots or unleashing a frightening roar. Despite these displays and the animals' obvious physical power, gorillas are generally calm and nonaggressive unless they are disturbed. Young gorillas, from three to six years old, remind human observers of children. Much of their day is spent in play, climbing trees, chasing one another and swinging from branches.
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