Mountain gorillas can be seen in Bwindi Impenetrable National Park and Mgahinga National Park in Uganda, Volcanoes National Park of Rwanda, and Virunga National Park of Congo (DRC) in peacetime. These gorillas share 97% biological makeup with humans and of all apes, gorillas are known to be the largest. It is believed that these large primates used to inhabit a swathe of land that covered most of central Africa but the ice age diminished the forests which divided their population into three; the eastern lowland and mountain gorillas and the western lowland gorillas.
Mountain gorillas are distinguished from lowland gorillas by longer hair, broader chests, and wider jaws which you can visibly witness on your gorilla trekking safari. Some experts also suggest that the gorillas in Bwindi are distinct species from the ones in the Virunga mountains as the gorillas in Bwindi are less shaggy which is major because of the lower altitude.
Nearly all gorillas live in humid equatorial rainforests, Mountain gorillas live in forests between 9200 and 11,200 ft (2800–3400 m), visit alpine meadows up to 13,000 ft (4000 m). Mist and clouds often obscure sun and night temperatures can go below freezing. Massive trees of a few species dominate but do not shade more than 50% of the landscape, which has dense undergrowth of tangled vines, stinging nettles, wild celery, and other herbaceous plants. Eastern lowland gorillas also live in mountains, northwest of Lake Kivu in tall, dense, variegated forest of Kahusi-Biega NP between 6600 and 8000 ft (2000–2500 m).
Mountain gorillas of eat leaves, shoots, and stems of some 58 different plants in 7 different vegetation zones. But 9 mainstay species made up 80% of all feeding records, and just 3 species made up 60%: a scraggly vine (Galium), a thistle, and a kind of celery. Stinging nettles, blackberries, and a small Vernonia tree are also important foods. Most of these items contain water which allows the mountain gorillas to survive a long while without drinking water. Roots, bark, grubs, snails, dirt, and dung are taken in small amounts to compensate for a diet deficient in vitamin B12, potassium, and calcium. Gorillas do not share food or use tools but are very skillful at opening and eating the palatable parts of each plant, whether roots, fruits, shoots, leaves, bark, pith, or grubs living in rotting wood.
Fairly regular daily pattern, varying from group to group, subject to greater daily variation in mountains (changeable weather conditions). Mountain gorillas huddle motionless in cold, rainy weather, and on sunny mornings often put off foraging to continue basking. On average day, a group spends 30% of time feeding, 30% traveling, and 40% resting, mainly at midday. Activities are closely synchronized, revolving around silverback leader. Daily ranging of Virunga gorillas, extremely variable, averages 380 to 600 yd (range 100–2700 yd).
Gorillas build nests in trees or on the ground to sleep in at night and most make nests for midday siesta. Group composition can be told by the number and size of nests and the dung deposited in them. Construction takes at most 5 minutes, as seated or standing gorilla pulls in, bends over, or breaks off branches, placing them around and underbody to form a crude platform or hollow with a roughly circular rim. Nests enable gorillas to sleep lying down, without falling from tree or rolling down steep slope.
A gorilla family consists of a number of silverback (adult) males, with or without harems of females and young. Home ranges overlap and change from year to year, have no sharp boundaries and are undefended. However, each gorilla family or lone male has a smaller core area where it spends most of its time, and different units normally avoid meetings except when silverbacks are intent upon adding females to their harems. A typical harem numbers 9 gorillas (range 2–20). The largest recorded group numbered is 37. A mountain gorilla group typically includes 1 mature silverback, 1 young adult blackback son (8–12 years old), 3 wives, and 2young (under 8 years). Different big groups of mountain gorillas have been known to contain up to 4 silverbacks (1 fully mature, the others grown sons), 5 blackbacks, 12 adult females, and 16 young.
Tough But so Gentle?
Before gorillas were studied in the wild, they were portrayed as about the most dangerous and savage of all wild beasts. Popular books and films based on studies of the mountain gorilla reversed that image, and the public now thinks of them as gentle, even pathetic giants driven to the edge of extinction by our species. This is the truer image: feeding and resting gorillas are as peaceful as cattle, and what remains of the mountain gorilla’s range is literally mountain tops standing as islands in a rising tide of humanity. But mature male gorillas are another matter.
The gorilla’s legendary ferocity is based on the spectacular charging displays of silverbacks defending their families. Thanks to the strong nerves of gorilla observers, we now know that 99% of their charges are bluff—the silverback rarely follows through and clobbers intruders. But if the objective is to intimidate enemies and keep them at a distance, the display is outstandingly successful. And if pressed, silverbacks will follow through—so, many have died, overwhelmed by the guns and spears of poachers (and, not so long ago, by museum and zoo collectors).
Benign as they may appear within the peaceful family setting, silverbacks are nonetheless despots, perhaps as fearsome to females and young as to puny humans. The silverback’s every wish is his troop’s command. He leads and makes all the decisions, emits 92% of the group’s calls, takes precedence whenever access to food or a mineral lick is limited and can quell boisterous or quarrelsome behavior with a look, frown, or grunt. Each female is bonded to him and not to other females; he is the common link between them and their offspring, and his wives compete to groom and stay closest to him. The alpha female and her youngsters are the best-protected family members. If a group is left leaderless by the death of the silverback, it tends to disintegrate.The reason male gorillas are so awesome has to do not with predators but with the rigorous sexual competition.
The average interval between births is 4 years; first birth at 9 to 12 years; gestation 8.5 months. Given a mortality rate of 46% of live births, as in Parc des Volcans, a female that lives 40 to 50 years may leave 2 to 6 progeny. Males are infertile until they become silverbacks at 11 to 13 years, but a silverback with 3 or 4 wives that lives 50 to 60 years leaves 10 to 20 offspring. One grizzled patriarch, estimated to be 55 to 60 years old, had 19 known descendants and was still in charge of a harem.
Like various animals with nonterritorial, polygynous mating systems (baboon, giraffe, elephant, buffalo, etc.), male gorillas mature much more slowly than females and continue growing into middle or old age, leading to a dominance hierarchy based on size and seniority. To compete for a harem, a male must have an established home range and the self-assurance to confront any rival. Few are mature and experienced enough before turning 15, maybe 4 years after becoming peripheral to and finally separating from their families.
A harem is acquired one female at a time, either by persuasion or conquest. Beginning in adolescence at around 8 years, females transfer to another group, usually at least twice; they become permanent members of the group in which they finally give birth. Some join large, established harems, but more elope with a lone silverback or join a small group. Since the first wife ranks highest and each newcomer has the lowest rank, lone silverbacks may be the best catch. Females are neither abducted by force from their harems nor forcibly detained by silverbacks, which rarely show sexual interest in immature females. Yet over of the transfers observed in the Parc des Volcans involved confrontations.
Most occur when a group contains a female in heat; hostilities may continue intermittently for days and involve adult females as well as all adult and subadult males. The defending silverback tries to intimidate rivals with hooting, chest beating, and display runs; meanwhile, his armpit glands give off a pungent smell humans can detect at 25 yd. Broken canines and healed head wounds present in ¾ of found adult male skulls attest to violent encounters. When a bold intruder charges right into a family, females are also likely to be injured as they seek to defend their offspring from infanticide. Killing a rival’s offspring is one way of competing for reproductive success it also serves to make mothers sexually receptive again within days or weeks.
During 1 to 2 day estrus, copulation occurs at c. 3-hour intervals, usually initiated by female. Male clasps her around waist and either sits upright or leans forward, while she squats, arms wide, hands on ground or holding male’s hands; or she rests on elbows with rump elevated. Rarely a couple copulates face to face. Both parties make thrusting motions and vocalize during the 1-to 2-minute act (range 15 sec.-20 min.). Copulation calls often attract attention of lone silverbacks; resident silverbacks become particularly irascible and vigilant when rivals are lurking in the undergrowth.
Female in heat often stimulates sexual behavior of other group members. Females mount other females and youngsters; young males mount and attempt to copulate with (usually female) peers. Group members keep away from a mature female in heat, but silverback may tolerate copulations with adolescent females.
Offspring and Parental Care
Though weighing only 4.5 lb (2 kg), newborn has coat and clings to mother’s front with hands and, less securely, with stubby toes. Gorillas develop about twice as fast as humans. An infant rescued from poachers crawled, bounced up and down, grinned, chuckled, and started to play at c. 8 weeks; walked and explored beyond arm’s length at 4 months when it would normally begin riding mother’s back. By 6 to 7 months a gorilla can already climb but continues to nurse until 1.5 to 2 years old. A growing youngster spends increasing time socializing and playing, mostly with its own siblings and parents unless there are playmates its own age. Older siblings and the silverback are gentle and protective an orphaned juvenile slept in the same nest with the silverback. Juvenile females are permitted to groom and carry infants.