Western Lowland Gorilla (Infant)

Western-Lowland-Gorilla-Infant---Gorilla-Gorilla-Gorilla-copia

Western Lowland Gorilla Infant – Gorilla Gorilla Gorilla

The western lowland gorilla (Gorilla gorilla gorilla) is one of two subspecies of the western gorilla (Gorilla gorilla) that lives in montaneprimary, and secondary forests and lowland swamps in central Africa in AngolaCameroonCentral African RepublicRepublic of the CongoDemocratic Republic of the CongoEquatorial Guinea and Gabon. It is the gorilla mostly found in zoos.[2] Adult male gorillas are prone to cardiomyopathy, a degenerative heart disease.

Physical description

The western lowland gorilla is the smallest subspecies of gorilla but nevertheless still a primate of 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 progressively 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 that of a human’s, and very large thumbs. They have short muzzles, a prominent brow ridge, large nostrils, and small eyes and ears. Other features are large muscles in the jaw region along with broad and strong teeth.[4]

A male standing erect can be 5–6 feet (1.5–1.8 m) tall and weigh 300–600 pounds (140–270 kg).[5] According to the Guinness Book of World Records, the average male is 168 kg (370 lb) and stands upright at 163 cm (64 in).[6] Males in captivity, however, are noted to be capable of reaching weights up to 275 kg.[4] Females stand 5 feet (1.5 m) tall and weigh half as much as males.[5] According to the late John Aspinall, a silverback gorilla in his prime has the physical strength of 7–8 Olympic weight lifters 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. This style of movement requires long arms, which works for western gorillas because the armspan of gorillas is larger than their standing height.

Behavior

Western lowland gorilla groups travel within a home range averaging 3–18 sq mi (7.8–46.6 km2). Gorillas do not display territorial behavior, and neighboring groups often overlap ranges.[7][8] 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 0.3–1.8 mi (0.48–2.90 km) 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.[9] Human hunters and leopards can also influence the movement patterns.

It was found that it is easier for males to travel alone and move between groups as a result of the solidarity they experienced before finding their own breeding group. 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.[10] However, while both sexes leave their birth group, females are never found alone; they just travel from breeding group to breeding group. It was also found that 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.[11] The male gorilla takes on the role of the protector. Females tend to make bonds with other females in their natal group only, but rather form strong bonds with males. Males also compete aggressively with each other for contact with females.[12]

The group of gorillas is led by one or more adult males. In cases where there are more than one silverback males 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.[13] They are often found on the ground, and are made up of up to 30 gorillas. Western lowland gorillas live in the smallest family groups of all gorillas, with an average of 4 to 8 members in each. The leader (the silverback) organizes group activities, like eating, nesting, and traveling 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 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.[14]

Reproduction

Female Western lowland gorillas do not produce many offspring due to the fact that they do not reach sexual maturity until the age of 8 or 9.[15] Female gorillas give birth to one infant after a pregnancy of nearly nine months. Unlike their powerful parents, newborns are tiny—weighing four pounds—and able only to cling to their mothers’ fur. These infants ride on their mothers’ backs from the age of four months through the first two or three years of their lives.[14] Infants can be dependent on their mother for up to five years.[15]

A study of over 300 births to captive female gorillas revealed that older females tend to give birth to more male offspring as opposed to females under 8 years old. This pattern is likely to result from selective pressures on females to have males at a time when they can provision them most effectively, as male reproductive success probably varies more than that of females and depends more on the maternal role.[16]

Female western lowland gorillas living in a group led by a single male have been observed to display sexual behavior during all stages of their reproductive cycle and during times of non-fertility. Three out of four females have been observed to engaged in sexual behavior while pregnant and two out of three females have been observed to engage in sexual behavior while lactating. Females are significantly more likely to engage and participate in sexual behavior and activity on a day when another female is sexually active. It has been found that the female western lowland gorillas participate in non-reproductive sexual behavior in order to increase her reproductive success through sexual competition. By increasing the female’s own reproductive success, she then decreases the reproductive success of others female gorillas, regardless of their reproductive state.[17]

Relationship with humans

The presence of western lowland gorillas has allowed humans to further the study of how gorillas compare with humans in regards to human diseases, behavior, linguistic, and psychological aspects of their lives. They are hunted illegally for their skins and meat in Africa and captured to be sold to zoos. While defended as being economically profitable for restaurants and local people, it is a large contributor to the endangered status of the western lowland gorilla. They are also seen as a crop pest in western Africa because they raid native plantations and therefore destroy what would have otherwise been valuable crops, with more importance being given to the human farming than the wildlife.[4]

Population decline and recovery

The western lowland gorilla population in the wild is faced by a number of factors that threaten its extinction. Such factors include deforestation, farming, grazing, and the expanding human settlements that cause forest loss. There is a correlation between human intervention in the wild with the destruction of habitats and increase in bushmeat hunting.[18] Another of these factors is infertility. Generally, female gorillas mature at 10–12 years of age (or earlier at 7–8 years) and their male counterparts mature slower, rarely strong and dominant enough to reproduce before 15–20 years of age.[19] The fecundity of females, or capacity of producing young in great numbers, appears to decline by the age of 18. Of one half of captive females of viable reproductive age, approximately only 30% of those had only a single birth. The long, narrow, bony pelvis of the great apes, which further contributes to the potentially long distance from the apex of the vagina to the ovaries and therefore decreases the chance of successful fertilization. However, these non-reproductive gorillas may prove to be a valuable resource since the use of assisted reproductive techniques aid in the maintaining of genetic diversity in the limited population(s) in zoos.[20]

In captivity

It is common for non-human primates kept in captivity to exhibit behaviors deviating from the normal behavior observed of them in the wilderness. A particular abnormal behavior is hair-plucking, which occurs across many species of mammals and birds. Studies made on the topic show that of all the western lowland gorillas housed in the Association of Zoos and Aquariums (AZA) population, 15% of the surveyed population displayed hair-plucking behavior with 62% of all institutions housing a hair-plucker. Individual gorillas, particularly those of a more solitary nature, are more likely to self-pluck using their fingers and pick up this behavior if they were exposed to a group member that plucked their hair as a youngster and not yet mature gorilla.[21]

Intelligence

Their intelligence is displayed through their ability to fashion natural materials into tools that help them gather food more conveniently. While the use and manufacture of tools to extract ants and termites is a well-documented behavior in wild chimpanzees, it has never been observed in other great apes in their natural habitat and never seen to be done by other primates in captivity. In terms of manufacturing tools for the use of extracting for western lowland gorillas, gorillas are able to adapt tools to a particular use by selecting branches, remove projections such as leaves and bark, and adapting their length to the depth of the holes. It appears they also anticipate the use of the tool since they begin with biggest sticks available and progressively modify it till it is the perfect fit for inserting into a hole that contains food. This demonstrates the gorillas’ acquisition of high level sensorimotor intelligence similar to that of young human children.[22] Another example of gorillas’ significant intelligence is their ability to comprehend simple sign language.[18] In the mid-1970s, researchers turned their attention to communicating with gorillas via sign language. One gorilla, Koko, mastered more than 1,000 signs. Studies of the mental capacity of western lowland gorillas continue.

Habitat

Western Lowland Gorillas primarily live in rain forests, swamp forest, brush, secondary vegetation, clearing and forest edges, abandoned farming fields, and riverine forests. They live in primary and secondary lowland tropical forests that have elevations that extend from sea level up to 1,300 meters. The average amount of rainfall in the areas where Western Lowland Gorillas typically reside is about 1,500 millimeters a year with the greatest rainfall between the months of August and November. Western Lowland Gorillas are not typically observed in areas that are close to human settlements and villages. They have been known to avoid areas with roads and farms that show signs of human activity. These gorillas favor areas where edible plants are more copious. Swamp forests are now considered important feeding areas and habitats for the western lowland gorilla. These areas support the gorillas in both the wet and the dry season of the forest.[23] The forests of the Republic of Congo are currently considered to host the majority of the western lowland gorilla population. The forests of the Republic of Congo serve as protection to the gorillas with the isolation of the large swampy forest areas.[24]

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