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Gorillas in Uganda at present are approximately 500 individuals in the Bwindi Impenetrable national park with 28 gorilla families, which is the largest number of habituated gorillas in Africa, these include 25 habituated troops, meant for gorilla tracking, as well as 3 non habituated groups, for the habituation experience.
Mountain gorillas are found in two protected areas in Uganda: Bwindi Impenetrable National Pork, a UNESCO world heritage site famous for harboring 459 mountain gorillas, which it almost half of the world’s mountain gorilla population, and Mgahinga Gorilla National Park, which is part of the Virunga Massif, a chain of 8 volcanic mountains that extend for 50 km² along the borders of Uganda, Rwanda and the Democratic Republic of Congo.
The general makeup of gorilla families tends to fluctuate from time to time due to several reasons such as migration of members. Therefore, the numbers given here are estimations by the Uganda Wildlife Authority (UWA) in August 2024.
Mountain Gorillas – The only Sub-species of Gorillas in Uganda
Evolution Taxonomy, and Classification
Mountain gorillas in Uganda are descendants of ancestral monkeys and apes found in Africa and Arabia during the start of the Oligocene epoch (34-24 million years ago) Fossil records provide evidence of hominoid primates (apes) found in East Africa approximately 22-32 million years ago, although the fossil record of the area where mountain gorillas lived is particularly poor and so Its evolutionary history is not clear.
It was about 8.8 to 12 million years ago that the group of primates who were to evolve into gorillas spilt from their common ancestors, humans and chimps: this is when the genus Gorilla emerged. Mountain gorillas have been isolated from eastern lowland gorillas for approximately 10.000 years and these two taxa separated from their western counterparts approximately 1.2 to 3 million years ago.
The genus was first referenced as Troglodytes in 1847, but renamed to Gorilla in 1852. It was not until 1967 that the taxonomist Colin Groves proposed that all gorillas be regarded as one species (Gorilla gorilla) with three subspecies Gorilla garilla gonila (western lowland gorilla), Gorilla gorilla gorilla (lowland gorillas found west of the Virungas) and Gorilla gorilla beringei (mountain gorillas, Including Gorilla beringei, found in the Virungas and Bwindi). In 2003, after a review, they were divided into two species (Gorilla gorilla and Gorilla beringei) by The World Conservation Union (IUCN), and there is now agreement that there are two species, each with two subspecies.
Unique Features of Mountain Gorillas
The fur of the mountain gorillas in Uganda, often thicker and longer than that of other gorilla species, enables them to live in colder temperatures. Gorillas can be identified by nose prints unique to each individual, much like a fingerprint.
Males reach a standing height of 161-171 cm (63-67 in), a girth of 138-163 cm (54-64 in), an arm span of 2 to 2.7 m (6 ft 7 in to 8 11 10 in) and a weight of 120-191 kg (265-421 lb). Females are smaller with a weight of 70-98 kg (154-216 lb). This subspecies is smaller than the eastern lowland gorilla, the other subspecies of eastern gorilla.
Adult males have more pronounced bony crests on the top and back of their skulls, giving their heads a mare conical shape. These crests anchor the powerful temporalis muscles, which attach to the lower jaw (mandible). Adult females also have these crests, but they are less pronounced.
Like all gorillas, they feature dark brown eyes framed by a black ring around the iris. Adult males are called silverbacks because a saddle of gray or silver-colored hair which develops on their backs with age. The hair on their backs is shorter than on most other body parts, and their arm hair is especially long.
The mountain gorilla is primarily terrestrial and quadrupedal however, it will climb into fruiting trees if the branches can carry its weight. Like all great apes other than humans, its arms are longer than its legs. It moves by knuckle-walking, supporting its weight on the backs of its curved fingers rather than its palms.
The mountain gorilla is diurnal, spending most of the day eating, as large quantities of food are needed to sustain its massive bulk. It forages in the early morning, rests during the late morning and around midday, and in the afternoon it forages again before resting at night.
Each gorilla builds a nest from surrounding vegetation to sleep in, constructing a new one every evening. Only infants sleep in the same nest as their mothers. They leave their sleeping sites when the sun rises at around 6 am, except when it is cold and overcast; then they often stay longer in their nests.
Distribution and Habitat Of Mountain Gorillas
The mountain gorilla inhabits the Albertine Rift montane cloud forest, including the Virunga Mountains, ranging in elevation from 2.200 to 4.300 m (7.200 to 14,100 ft), in Uganda, Rwanda, and the Democratic Republic of Congo
The vegetation is very dense at the bottom of the mountains, becoming sparser at higher elevations. and the forests are often cloudy, misty and cold. The mountain gorilla also occasionally uses the border habitat with the Rwenzori-Virunga montane moorlands, at elevations higher than the Albertine Rift montane cloud forest.
Uganda is home to over 50% if all mountain gorilla remaining in the world. They can be found in Bwindi Impenetrable National Park and Mgahinga Gorilla National Park
Behaviors and Ecology of Mountain Gorillas in Uganda
The home range used by one group of gorillas during one year is influenced by availability of food sources and usually includes several vegetation zones. George Schaller identified ten distinct zones, including: bamboo forest al 2,200-2,800 m (7,200-9,200 ft): Hagenia forest at 2,800-3,400 m (9,200-11,200 ft); and the giant senecio zone at 3,400-4.300 m (11.200-14,100 ft).
The mountain gorillas in Uganda spends most of its time in Hagenia forest, where gallium vines are found year-round. All parts of this vine are consumed: leaves, stems, flowers, and berries. It travels to the bamboo forest during the few months of the year when fresh shoots are available, and it climbs into subalpine regions to eat the soft centers of giant senecio trees.
Diet Of Mountain Gorillas – What they Eat
The mountain gorilla is primarily a herbivore; the majority of its diet is composed of the leaves, shoots, and sterna (85.8%) of 142 plant species. It also feeds on bark (6.9%), roots (3.3%), flowers (2.3%), and fruit (1.7%), as well as small invertebrates. (0.1%), in a yearlong study in Bwindi Impenetrable Forest adult males ate an average of 18.8 kg (4) lb) of food a day, while females ate 14.9 kg (33 lb).
Social Structure of Mountain Gorillas
Gorillas live in families called troops.
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 nonterritorial: the silverback generally defends his troop rather than his territory. Amongst the Virunga mountain gorillas, the average length of tenure for a dominant silverback 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 lane 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 silverback, who is the group’s undisputed leader, another subordinate silverback (usually a younger brother, half-brother, or even an adult son of the dominant silverback); one or two blackbacks, who act as sentries, three to four sexually mature females, who have bonded for life to the dominant silverback, and from three to six juveniles and infants.
The bond that a silverback has with his females forms the core of gorilla social life. Bonds between them are maintained by grooming and staying close together. Females form strong relationships with males to gain mating opportunities and protection from predators and infanticidal outside males. However, aggressive behaviors between males and females do occur, but rarely lead to serious injury.
Relationships between females may vary. Maternally related females in a troop tend to be friendly towards each other and associate closely. Otherwise, females have few friendly encounters and commonly act aggressively towards each other
Females may fight for social access to males and a male may intervene. Male gorillas have weak social bonds, particularly in multiple-male groups with apparent dominance hierarchies and strong competition for mates.
Most males and approximately 60% of females leave their natal troop. Males leave when they are about eleven 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 two-five years before they can attract females to join them and form a new troop. Females typically emigrate when they are about eight years old, either transferring directly to an established troop or beginning a new one with a lone male. Females often transfer to a new group several times before they choose to settle down with a certain silverback male.
The dominant silverback generally determines the movements of the troop, leading it to appropriate feeding sites throughout the year. He also mediates conflicts within the group and protects it from external threats. When the troop is attacked by humans, leopards, or other gorillas, the silverback will protect them, even af the cost of his own life. He is the center 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 troop, the silverback is usually the one who looks after her abandoned offspring, even allowing them to sleep in his nest. Young mountain gorillas have been observed searching for and dismantling poachers’ snares.
When the silverback 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 troop will either split up or adopt an unrelated male, When a new silverback joins the family group, he may kill all of the infants of the dead silverback. Infanticide has not been observed in stable groups, in a single male troop, when the silverback dies, the females and their offspring disperse and find a new troop.
Reproduction and Parenting
Females mature at 10-12 years, and males at 11-13 years.
A female’s first ovulatory cycle occurs when she is six years of age, and is followed by a two-year period of adolescent infertility. The estrous cycle lasts 30-33 days, with outward ovulation signs subtle compared to those of chimpanzees. The gestation period lasts 8.5 months. Female mountain gorillas first give birth at 10 years of age and have four-year interbirth intervals. Males can be fertile before reaching adulthood. Gorillas mate year-round.
Females will pursue their lips and slowly approach a male while making eye contact. This serves to urge the male to mount her, if the male does not respond, then she will try to attract his attention by reaching towards him or slapping the ground. In multiple-male groups, solicitation indicates female preference, but females can be forced to mate with multiple males. Males incite copulation by approaching a female and displaying at her or touching her and giving a “train grunt”. Recently, gorillas have been observed engaging in face-to-face sex, a trait once considered unique to humans and bonobos.
Gorilla infants are vulnerable and dependent, thus mothers, their primary caregivers, are important to their survival. Male gorillas are not active in caring for the young, but they do play a role in socializing them to other youngsters. The silverback has a largely supportive relationship with the infants in his troop and shields them from aggression within the group. Infants remain in contact with their mothers for the first five months and mothers stay near the silverback for protection, infants suckle at least once per hour and sleep with their mothers in the same nest.
Infants begin to break contact with their mothers after five months, but only for a brief period each time. By 12 months old, infants move up to 5 m (16 (1) away from their mothers. Al around 18-21 months, the distance between mother and offspring increases and they regularly spend time away from each other. In addition, nursing decreases to once every two hours, infants spend only half of their time with their mothers by 30 months. They enter their juvenile period in their third year, and this lasts until their sixth year. At this time, gorillas are weaned and they sleep in a separate nest from their mothers. After their offspring are weaned. females begin to ovulate and soon become pregnant again. The presence of play partners, including the silverback. minimizes conflicts in weaning between mother and offspring.
The Dominant Silverback
A silverback mountain gorilla is an adult male identifiable by the swathe of silver hair on its back. As well as this impressive signifier of maturity, they are famed for displays of aggression and dominance including whooping, charging, chest beating, free slapping, and less commonly, physical duels.
A typical silverback weighs 430 pounds (195 kg) and stands 5 feet (1.5m) tall. Silverbacks are Incredibly strong and can lift over 1763 pounds (800kg) of dead weight. That’s roughly twice as much as a well-trained weightlifter. In the wild, a silverback uses its Immense strength to fell trees in order to reach their fruits. This makes mountain gorillas a keystone species in Bwindi and Mgahinga, since they significantly affect the ecology of their environment.
A dominant silverback is responsible for directing troop activities such as nesting, feeding and migration between seasonal feeding areas. While vying to retain and recruit females during clashes with other troops, a dominant silverback will defend members of his troop to the death.
Despite a dominant silverback retaining mating rights over all females within his troop, higher ranking silverbacks in multi-male groups are often able to mate with a small proportion of females.
Blackbacks and Subordinate Silverbacks
The ultimate goal of all silverbacks is to maximize chances of reproductive success by becoming dominant. A blackback is mature sexually but not physically strong enough to challenge for dominance. Once a male develops into a silverback, he may then form a coalition with the dominant silverback or challenge for control of the troop.
Internal conflicts between silverbacks normally constitute displays of aggression rather than physical contact. However, fights do occur, sometimes to the death.
Coalitions may lead to subordinate males preventing females from migrating during clashes with rival troops.
Although it may appear the subordinate silverback is defending the position of the dominant silverback, his true motivation is to retain access to females within the troop in the hope of one day deposing the dominant silverback. An alternative to coalition forming or challenging for dominance is for a silverback to become solitary.
Communication among Gorillas
Gorillas communicate for Identification of appropriate species, gender and reproductive status of potential mates, predator avoidance/protection, and the maintenance of social relationships.
Twenty-five distinct vocalization are recognized, many of which are used primarily for group communication within dense vegetation. Sounds classified as grunts and barks are heard most frequently while travelling and indicate the whereabouts of the individual troop members. They may also be used during social interactions when discipline is required. Screams and roars signal alarm or warning and are produced most often by silverbacks.
Deep, rumbling belches suggest contentment and are heard frequently during feeding and resting periods. They are the most common form of intragroup communication.
For this reason, conflicts are most often resolved by displays and other threat behaviors that are intended to intimidate without becoming physical. As a result, fights do not occur very frequently.
Body postures and facial expressions are also used to communicate the gorilla’s mood.
Aggression
Although strong and powerful, mountain gorillas are generally gentle and very shy. Severe aggression is rare in stable groups, but when two mountain gorilla troops meet, sometimes the two silverbacks can engage in a fight to the death, using their canines to cause deep, gaping injuries. Conflicts are most often resolved by displays and other threat behaviors that are intended to intimidate without becoming physical.
A 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 their palms.
A gorilla’s chest-beat may vary in frequency depending on its size. Smaller ones tend to have higher frequencies, while larger ones tend to be lower. They also do this the most when females are ready to male.
Affiliation
The midday rest period is an important lime for establishing and reinforcing relationships within the family. Mutual grooming reinforces social bands, and helps keep hair free from dirt and parasites. It is not so common among gorillas as in other primates, although females groom their offspring regularly.
Young gorillas play often and are more arboreal than the large adults. Playing helps them learn how to communicate and behave within the group. Activities include wrestling, chasing, and somersaults. The silverback and his females tolerate and, if encouraged, even participate
Intelligence in Mountain Gorillas
Gorillas in Uganda and others across the world are considered highly intelligent. A few individuals in captivity, such as Koko, have been taught a subset of sign language.
Much like humans, gorillas can laugh when they’re tickled and cry when they’re hurt. They grieve, develop strong family bonds, make and use fools, and think about the past and future,
Some researchers believe gorillas have spiritual feelings or religious sentiments. They have been shown to have cultures in different areas revolving around different methods of food preparation, and will show individual color preferences.
Genetically, humans share more than 96% of their DNA, with gorillas. We are indeed very closely related to our ape counterparts. But the small differences between us have led to some extraordinarily big outcomes.
