The Mountain Gorilla
Mountain gorillas are found in three countries Uganda, Rwanda & Democratic Republic of Congo. The mountain gorilla (Gorilla beringei beringei) is one of the two subspecies of the eastern gorilla. There are two populations. One is found in the Virunga volcanic mountains of Central Africa, within three National Parks: Mgahinga, in south-west Uganda; Volcanoes,in north-west Rwanda; and Virunga in the eastern Democratic Republic of Congo (DRC). It is listed as critically endangered by the IUCN. The other is found in Uganda’s Bwindi Impenetrable National Park. Some primatologists consider the Bwindi population in Uganda may be a separate subspecies, though no description has been finalized. As of September 2016, the estimated number of mountain gorillas remaining is about 880.
The mountain gorilla is highly social, and lives in relatively stable, cohesive groups held together by long-term bonds between adult males and females. Relationships among females are relatively weak. These groups are non-territorial; the silver-back generally defends his group rather than his territory. In the Virunga mountain gorillas, the average length of tenure for a dominant silver-back is 4.7 years.
61% of groups are composed of one adult male and a number of females and 36% contain more than one adult male. The remaining gorillas are either lone males or exclusively male groups, usually made up of one mature male and a few younger males. Group sizes vary from five to thirty, with an average of ten individuals. A typical group contains: one dominant silver-back, who is the group’s undisputed leader; another subordinate silver-back (usually a younger brother, half-brother, or even an adult son of the dominant silver-back); one or two black-backs, who act as sentries; three to four sexually mature females, who are ordinarily bonded to the dominant silver-back for life; and from three to six juveniles and infants.
Most males, and about 60% of females, leave their natal group. Males leave when they are about 11 years old, and often the separation process is slow: they spend more and more time on the edge of the group until they leave altogether. They may travel alone or with an all-male group for 2–5 years
before they can attract females to join them and form a new group. Females typically emigrate when they are about 8 years old, either transferringd
irectly to an established group or beginning a new one with a lone male. Females often transfer to a new group several times before they settle down with a certain silver-back male.
The dominant silver-back generally determines the movements of the group, leading it to appropriate feeding sites throughout the year. He also mediates conflicts within the group and protects it from external threats. When the group is attacked by humans, leopards, or other gorillas, the silver-back will protect them even at the cost of his own life. He is the centre of attention during rest sessions, and young gorillas frequently stay close to him and include him in their games. If a mother dies or leaves the group, the silver-back is usually the one who looks after her abandoned offspring, even allowing them to sleep in his nest. Experienced silver-backs are capable of removing poachers’ snares from the hands or feet of their group members.
When the silver-back dies or is killed by disease, accident, or poachers, the family group may be disrupted. Unless there is an accepted male descendant capable of taking over his position, the group will either split up or adopt an unrelated male. When a new silver-back joins the family group, he may kill all of the infants of the dead silver-back. Infanticide has not been observed in stable groups.
Although strong and powerful, the mountain gorillas are generally gentle and very shy. Severe aggression is rare in stable groups, but when two mountain gorilla groups meet, the two silver backs can sometimes engage in a fight to the death, using their canines to cause deep, gaping injuries. For this reason, conflicts are most often resolved by displays and other threat behaviours that are intended to intimidate without becoming physical. The ritualized charge display is unique to gorillas.
The entire sequence has nine steps: (1) progressively quickening hooting, (2) symbolic feeding, (3) rising bipedally, (4) throwing vegetation, (5) chest-beating with cupped hands, (6) one leg kick, (7) sideways running four-legged, (8) slapping and tearing vegetation, and (9) thumping the ground with palms
Conservation efforts have led to an increase in overall population of the mountain gorilla (Gorilla beringei beringei) in the Virungas and at Bwindi. The overall population is now believed to be at least 880 individuals. Three more – infants who suffered a traumatic poaching experience, injuries from snares, and/or losing their mothers in brutal killings – are currently in care of the Senkwekwe Centre orphanage in the DR of Congo.
In December 2010 the official website of Virunga National Park announced that “the number of mountain gorillas living in the tri-national forested area of which Virunga forms a part, has increased by 26.3% over the last seven years – an average growth rate of 3.7% per annum.” The 2010 census estimated that 480 mountain gorillas inhabited the region. The 2003 census had estimated the Virunga gorilla population to be 380 individuals; which represented a 17% increase in the total population since 1989 when there were 320 individuals. The population has almost doubled since its lowest point in 1981, when a census estimated that only 254 gorillas remained.
The 2006 census at Bwindi indicated a population of 340 gorillas, representing a 6% increase in total population size since 2002 and a 12% increase from 320 individuals in 1997. All of those estimates were based on traditional census methods using dung samples collected at night nests. Conversely, genetic analyses of the entire population during the 2006 census indicated there were only approximately 300 individuals in Bwindi. The discrepancy highlights the difficulty in using imprecise census data to estimate population growth.
In both Bwindi and the Virungas, groups of gorillas that were habituated for research and ecotourism have higher growth rates than unhabituated gorillas, according to computer modeling of their population dynamics. Habituation means that through repeated, neutral contact with humans, gorillas exhibit normal behavior when people are in proximity. Habituated gorillas are more closely guarded by field staff and they receive veterinary treatment for snares, respiratory disease, and other life-threatening conditions. Nonetheless, researchers recommended that some gorillas remain
unhabituated as a bet-hedging strategy against the risk of human pathogens being transmitted throughout the population.
Despite their recent population growth, the mountain gorilla remains threatened. As of 2008, mountain gorillas were listed as Critically Endangered on the IUCN Red List and are dependent on conservation efforts to survive.
David Agneya has worked with gorillas for many
years as tracker and guide. Here’s a link to get an extraordinary Gorilla Tracking experience