Western lowland gorilla

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 Repub...

Western lowland gorillas primarily live in rainforest, swamp forest, brush, secondary vegetation, clearing and forest edges, abandoned farming fields and riverine forest. They live in primary and secondary lowland tropical forest at elevations that extend from sea level up to 1,300 m (4,300 ft). The average amount of rainfall in the areas where western lowland gorillas typically reside is about 1,500 mm (60 in) 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 forest is now considered an important food source and habitat for the western lowland gorilla. These areas support the gorillas in both wet and dry seasons. The forest of the Republic of the Congo is currently considered to host the majority of the western lowland gorilla population. The isolation of the large swampy forest areas protects the gorillas.

Equatorial Guinea

The western lowland gorilla is primarily herbivorous, and its main diet consists of roots, shoots, fruit, wild celery, tree bark and pulp, which are found in the thick forest of Central and West Africa. During the wet season, gorillas commonly consume fruits. In the dry season, they eat less fleshy fruits, but they continue to eat other kinds of fruits. The diversity of fruits consumed was higher in a poor fruit year, when favored fruit species failed to produce large crops. They may also eat insects from time to time. The common food item which provides fibers is herbaceous stems. Important food species have been divided into three categories: staple foods which are eaten on a daily/weekly basis throughout the year; seasonal foods which are present in the majority of resources when available; and fallback foods which are always available, but eaten only or mainly during fruit-scarce months. The adult will eat around 18 kg (40 lb) of food per day. Gorillas will climb trees up to 15 meters in height in search of food. They never completely strip vegetation from a single area, since the rapid regrowth of the vegetation allows them to stay within a reasonably confined home range for extended periods of time. They eat a combination of fruits and foliage, providing a balance of nutrients, depending on the time of year. However, when ripe fruit is available, they tend to eat more fruit as opposed to foliage. When ripe fruit is in scarce supply, they eat leaves, herbs and bark. During the rainy months of July and August, fruit is ripe; however, in the dry seasons, ripe fruit is scarce. Gorillas choose fruit that is high in sugar for energy, as well as fiber.

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.

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. Female gorillas give birth to one infant after a gestation period of nearly nine months. Female gorillas do not show signs of pregnancy. Unlike their powerful parents, newborns are tiny, weighing 4 lb (1.8 kg), but are able 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. Infants can be dependent on their mother for up to five years. 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. 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 engage 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 female western lowland gorillas participate in non-reproductive sexual behavior in order to increase their reproductive success through sexual competition. By increasing the female's own reproductive success, she then decreases the reproductive success of other female gorillas, regardless of their reproductive state. Infanticide by adult male gorillas has occasionally been observed in this subspecies. Victims are never related to the killer. A male does this in order to have the opportunity to mate with the mother, who otherwise would be unavailable while caring for her young offspring.

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.

==== Hunting and logging ==== In tropical forest, gorillas are hunted to provide meat for the bushmeat trade. Logging also destroys gorilla habitats, although it may also provide increased herbaceous vegetation as a result of gaps in the tree cover. Destruction of gorilla habitat may harm the overall forest ecosystem. Western lowland gorillas are seed dispersers, which is beneficial to many of the animals in the forest, so their extinction could affect many other animals, which could over time destroy their current ecosystem. ==== Population decline and recovery ==== The western lowland gorilla population in the wild faces a number of threats to its survival. These 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 an increase in bushmeat hunting. Another threat is infertility. Generally, female gorillas mature at 10–12 years of age (or earlier at 7–8 years). Males mature more slowly: they are rarely strong and dominant enough to reproduce before 15–20 years of age. The fecundity of females (their capacity to produce young in great numbers) appears to decline by the age of 18. Of one half of captive females of viable reproductive age, approximately 30% of those had only a single birth. However, those gorillas that do not reproduce may prove to be a valuable resource, since the use of assisted reproductive techniques helps to maintain genetic diversity in the limited populations in zoos.

In the 1980s, a census of the gorilla populations in equatorial Africa was thought to be 100,000. Researchers later adjusted the figure to less than half because of poaching and diseases. Surveys conducted by the Wildlife Conservation Society in 2006 and 2007 found about 125,000 previously unreported gorillas have been living in the swamp forests of Lake Télé Community Reserve and in neighboring Marantaceae (dryland) forests in the Republic of the Congo. However, gorillas remain vulnerable to Ebola, deforestation and poaching. In 2002 and 2003, there was an Ebola outbreak in the Lossi sanctuary population, and in 2004, there was an Ebola outbreak in the Lokoué forest clearing in Odzala-Kokoua National Park, both in the Republic of the Congo. The Ebola outbreak in the Lokoué forest clearing negatively affected the individuals living in groups and the adult females more than the solitary males, resulting in an increase in the proportion of solitary males to those living in groups. This population decreased from 377 individuals to 38 individuals two years after the outbreak and to 40 individuals six years after the outbreak. The population is still slowly recovering, even today, it is hoped, towards a population that has the same demographic structure as an unaffected population, because of new births and breeding groups. This Ebola outbreak also affected the Maya Nord population (52 kilometres northwest from Lokoué) from 400 individuals to considerably fewer. Because of these outbreaks, the International Union for Conservation of Nature (IUCN) updated the status of western lowland gorillas from "endangered" to "critically endangered". In the northeastern part of the Republic of the Congo, western lowland gorillas are still being hunted for their bushmeat and the young for pets; five percent of the subspecies is killed each year because of this. Deforestation of this area allows for the trade of bushmeat and even more poaching. Commercial poaching of chimpanzees, forest elephants and western gorillas in the Republic of the Congo resulted from the increased amount of commercial logging and infrastructure. Deforestation and logging allowed for the creation of roads which allowed hunters to hunt deeper into the forest, increasing the amount of poaching and bushmeat trade in the area. The Republic of the Congo has put in place a conservation effort to conserve different species such as chimpanzees, forest elephants and western gorillas from poaching and deforestation. This conservation effort would allow these species to benefit from vegetation and ecologically important resources. Bush meat hunting and timber harvesting in the western lowland gorilla's habitat have negatively affected the probability of its survival. The western lowland gorilla is considered to be critically endangered by the IUCN. The western lowland gorillas, like many gorillas, are essential to the composition of the rainforest due to their seed distribution. The conservation of the western lowland gorilla has been made a priority by many organizations. The Wildlife Conservation Society (WCS) has been working with the local community in the Congo Basin to establish wildlife management programs. The WCS is also working in Congo and surrounding countries to limit the bush meat trade by enforcing laws and hunting restrictions and also helping the local people find new sources of protein. Zoos worldwide have a population of 550 western lowland gorillas, and the Cincinnati Zoo leads the United States in western lowland gorilla births.

The presence of western lowland gorillas has allowed the study of how gorillas compare with humans in regard to human diseases, behavior, and 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 economically profitable for restaurants and local people, such hunting contributes greatly to the endangered status of the western lowland gorilla. They are also seen as a crop pest in western Africa, because they raid plantations, and so destroy valuable crops.