Mountain gorillas inhabit the highlands of Uganda, Rwanda and Congo. They evolved half a million years ago, with the rise of the Virunga volcanoes, becoming larger than lowland gorillas and with thicker fur. Discovered in 1902, their groups consist of 10-20 members and they live 30-50 years. There are only about 880 mountain gorillas in existence but their number is increasing.
Mountain gorillas use vocalisations, physical gestures and movement to communicate. Their contact grunts are very important for group cohesion and coordination.
Females reach sexual maturity at eight years and mate with some or all males in the group. Pregnancy is 8.5 months and there are 3-4 years between births. At birth they weigh 1.5-2kg (4lb) and after four months ride on their mother’s back.
A silverback is an adult male, over 12 years old, with a distinctive patch of silver hair on his back and large canine teeth. He is the group leader, makes all the decisions, mediates conflicts, leads them to feeding sites and is responsible for defence, safety and well-being.
Related on the Gorilla Highlands blog:
• “Mountain Gorillas” blog category
Compared to the mountain gorilla, the golden monkey is a mystery. They share the environment and are also endangered, yet much less research has been done on them.
Golden monkeys, a subspecies of Blue Monkey, are endemic to the Virunga Volcanoes. Their lifespan is about 20 years and their population is estimated between 2,000 and 4,000. They are beautiful animals with an orange body and glossy black legs and head. Female colours are more golden and deeper, males look duller and lighter.
Within their bamboo and montane forest habitat that lies between 2,350 and 2,900m (7,710-9,515ft), all levels of the forest and canopy are important. Golden monkeys have forward facing eyes that allow them to focus on a single object and judge depth and distance, a critical ability for life in the bush. They are active by day and do not make night nests; they sleep in groups of four on top of bamboo culms. Sleeping sites are chosen for good shelter against the wind and decent access to the food range.
They descend to the forest floor to feed on bamboo shoots whenever they are in season. Golden monkeys also eat tender parts of bamboo and other leaves, fruits and flowers. There are variations between groups; some eat more fruit, others more leaves and flowers. Their intake of dead wood is a likely source of dietary sodium. Pregnant and lactating females sometimes consume insects. Golden monkeys have cheek pouches for food storage and opposable thumbs for better food manipulation.
A dominant male determines where the troop feeds, sleeps, rests; he is in charge for 1 to 8 years. There is a hierarchy among the females who all remain in their natal troop. On the move, females are first, followed by their offspring, while the male is at the rear. They communicate through a range of vocalisations, facial expressions and body language that scientists are still attempting to decipher.
Mating and births coincide with the rains and food availability. It is the females that solicit for male attention. The dominant male allows lone males to temporarily join and mate with females, thus widening genetic diversity within the troop. Mothers carry their infants on the belly and juveniles on the back. They have the lowest infant-to-female ratio of the eight monkey subspecies but it is unknown whether this is due to their evolution or a response to nutritional stress caused by disturbance and habitat loss.
Golden monkeys’ predators are crowned eagles and golden cats but the biggest threat comes from humans who illegally cut bamboo.
Bwindi is the only place on Earth where chimpanzees share the same habitat as mountain gorillas. However their niches are very different with little overlap and no interactions between them have been recorded.
Chimps were about 860 in Bwindi in the late 1990s but only 300–400 ten years later. Adults of both sexes can weigh 45kg/100lb, though females may be only 30kg/66lb.
Chimpanzee social structure is markedly different from other primates, being communities of individuals who share a range and freely join or split.
Males remain in their natal community, while females tend to emigrate. Mothers can form matrilineal groups with their offspring and, sometimes, grand-offspring. Group size varies from one to 40, the latter during food abundance or whenever females are in oestrous.
Both sexes take defensive duties, but males are the principal defenders of the community’s range against neighbouring groups. Females become sexually mature at 11–13 years and advertise oestrus with a prominent pink perineal swelling. They may mate with many males though not necessarily during oestrus. Gestation is eight months and birth intervals are around every five years. Mothers invest more time, up to seven years, in raising infants and transmitting learned behaviour.
Chimpanzees travel long distances easily, usually on the ground, over a large home range of around 10km²/3.8mi². They focus on patches with valuable high-energy food, such as the wild fig (85% of their diet), mostly in the middle and top layers of canopy forest. It used to be thought that chimpanzees were vegetarian but part of their diet is also different mammals, such as monkeys and duikers, and abundant insects— harvested or extracted with twig tools.
Chimpanzees don’t have specific nesting places and nightly make new nests with flexible branches bent into a dishshaped platform and lined with leaves. These are very similar to gorillas’ nests and are told apart by their faeces, which they both deposit sometime during the night.
Photo: Marcus Westberg
The baboon is not strictly a forest species and prefers savannah environments. Nowadays it lives at the forest’s margins as humans have taken over its normal habitat. It climbs trees only to sleep and forage for fruit.
Baboon adults weigh up to 50kg/110lb (male) or 30kg/66lb (female). Groups contain up to 45 individuals with several mature males, but may split into two when foraging.
Females breed every two years and their gestation is six months. Infants, black for the first six months, ride clinging to the mother’s belly and then on her back. Males have manes of long hair around the neck and shoulders.
In the wild grasses, fruit, insects and small animals make up the majority of their diet; mostly plant food. However baboons are committed and experienced raiders of farmland and a major threat to crops, poultry and incomes. The result is that they are treated as vermin and killed when discovered. Consequently baboons may have become nearly extinct in Echuya Forest with only a small population in Bwindi, about 1,000 in the late 1990s.
Photo: Marcus Westberg
Black and White Colobus
There are five species and eight sub species of colobus in Africa; the black and white colobus is found in Bwindi. The name comes from a Greek word meaning ‘crippled’, as these monkeys lack thumbs. They are further distinguished by having rump callosities, close set nostrils, tubular ears and no cheek pouches. In mountains they have longer and thicker fur. Bwindi’s colobus population was about 400 in the late 1990s.
Colobus are mainly arboreal and can jump long distances, though their tails are not prehensile. They are not the most active of primates and spend their afternoons resting and grooming. They may only move 350m/1,150ft in a day as that’s all it may take to eat 2–3kg/4.4–6.6lb of leaves. Home ranges are very small. Visual and vocal displays avoid, or minimise, competition and aggression between groups.
The colobus has a three-chambered stomach capable of extracting cellulose from its diet of 50–90% leaves. Competition from other primates is not an issue as it is the only species capable of prospering on such a diet. Open forest edges where young more digestible leaves are at their most plentiful are favoured. Other foods include fruit, bark, moss, insects and soil.
Groups are small with 1–3 adult males, 2–4 adult females and offspring. Females breed every two years and gestation lasts 5.5 months. Females are not the most competent of mothers and make terrible baby-sitters; the most common source of infant mortality is being dropped from a tree. Bachelor males may band together or follow a family troop but keep a low profile until such time that they may take over from a leader.
The colobus’ main predators are golden cats, crowned hawk eagles, dogs and chimpanzees. Humans have hunted them for ceremonial use and trade since historic times; the first possible reference come from Marco Polo in the late 13th century. Skins were commonly used to make coats and hats.
Photo: Blasio Byekwaso
Redtail monkeys have seven sub species with various hybrids in Africa, in the area between Uganda and Cameroon. The Uganda redtail is found in Bwindi; they have spread east and west in recent times and have therefore recently evolved.
The redtail is the smallest primate in Bwindi, adults weigh 3– 4 kg/6.6–8.8lb (female/male), and they are the most numerous; about 5,500 in the late 1990s,. They move rapidly and are very agile, but don’t go above 1,800m/5,900ft. Groups of 30– 35 are single male and multi female. There are about 132 individuals per km² (515 individuals per mi²) and home ranges are 1.3–24km² (0.5–9mi²).
Males compete in the groups and may join another group; if a male is completely unsuccessful he may pair off with a female of another sub species. Females stay with their natal group; they are responsible for most inter-group aggression and infighting but will join together to defend against a male if he attacks a female. Females are sexually mature at 4–5 years and they breed every 1–2 years. Infanticide is rare.
Redtails feed over a wide area in search of sparsely distributed fruits. Disturbed and secondary growth forest are preferred while their light weight gives them access to more precarious fragile branches than their heavier competitors. They eat 1kg/2.2lb at a time and use cheek pouches for storage. Less time is spent with their favourite wild fig than expected and more on smaller, more difficult to find, fruits. It may be that competitive pressure has forced them to diversify and depend on less nutritious and popular food. Insects are hunted by stealth; sneaking up and pouncing, rather than digging them up.
The redtails’ main predators are large raptors. Open spaces, particularly on trees, are avoided and their association with blue monkeys provides an extra set of eyes. They are rarely found on their own on fig trees or on open ground: it is far too dangerous. Some farmers see them as a pest because of crop raiding but not all troops have this habit.
Photo: Blasio Byekwaso
Blue monkeys are the most widespread primate in the forests of southwestern Uganda with about 3,000 each in Bwindi, the Virungas and Echuya Forest (132 groups). Adults weigh between 3.5kg/7.7lb (female) and 6kg/13lb (male). Groups of 30–35 are single male and multi female. Population density is 41 individuals per km²/16o per mi².
Blue monkey behaviour is similar to the redtail. Females are sexually mature at 5–6 and breed every two years with a slow annual increase. Infanticide is rare.
The blue monkey forages in the middle canopy layer in disturbed and open forest. Wild figs are its favourite food; it mostly eats fruit but also insects and plant leaves when there is none. Large raptors are the blues’ main predator, however, they are less vulnerable than other primates due to their size.
Photo: Blasio Byekwaso
Very little is known about the mountain monkey (also known as L’Hoest monkey) as they are rare, secretive and suspicious with an estimated 1,000 in Bwindi in the late 1990s. As adults they weigh 3–6kg /6.6– 13lb (female/male). Group size average is 25–30 but their territorial and social structure is not well-known; it may be similar to the blues and redtails.
Mountain monkeys tend to feed low, foraging 60% of their time below 5m/16ft. within a 7–10km²/2.7–3.9mi² area. They spend more time than other species on the ground, which may protect them against aerial predation in daytime, but sleep in tall trees to avoid nocturnal terrestrial carnivores. Their diet is fruit 40% (wild figs where possible), bushy growth 30% and insects 15%. The quantity and quality of food at this level is the poorest of the forest.
The golden cat is the main predator, though raptors who can swoop through the low canopy may also be significant. They sometimes raid crops and were previously hunted in Bwindi and the Rwenzori Mountains for their skins to make shoulder bags.
Elephants in the Gorilla Highlands can be of two species, the forest elephant (Loxodonta africanus cyclotis) and the savannah elephant (Loxodonta africanus). The main differences are the numbers of nails on their feet, the shape of their ears and tusks. The forest elephant has straighter tusks and was therefore preferred by ivory craftsmen.
Forest and savannah elephant ranges overlap and there may be interbreeding. The elephants in Bwindi are originally from the savannah further north but got stuck in the park and adapted to it. Current Bwindi statistics are a little vague with estimates of 30–50, roughly the same as eight years ago.
Elephants are slow breeders, with usually only one infant every five years. The female is receptive for 3–6 days at a time and advertises it with a low growl that can be heard for several kilometres. Gestation takes two years.
They utilise about 78 plant species in Bwindi, but concentrate on nine principal foods types. Overall their diet is made up of 62% trees, 12% bushes, and 25% herbs, climbers, grasses and sedges: fruit is rare. They focus on bark in the dry season and bamboo in the wet. Geographically they feed on bamboo shoots at high altitudes during the wet season, then move to Mubwindi Swamp (water source) in the dry and forage around mature forests.
The impact of elephants on trees is divided into bark stripping and damage by toppling and breaking. More trees are stripped in the bamboo zone while more are broken in mixed forest; they also tend to cause more tree damage at the forest’s edge and near rivers and other permanent water sources. Overall elephants increase forest stress but disperse seeds, maintain structure and prevent bush encroachment.
The pygmy elephant has been widely reported in Congo and southwestern Uganda but little studied. It is thought to be a morph of the forest species. Its smaller size may be an adaptation to either dense forest or high altitudes at the periphery of its range.
Photo: Blasio Byekwaso
There are two buffalo types in Uganda, the common Cape Buffalo (Syncerus caffer caffer) and Forest Buffalo (Syncerus caffer nanus). The latter are currently only found in the Virungas and elsewhere in the forests, mostly lowland, of Africa.
The well known Cape buffalo is one of the iconic species of Africa and unlike its Asian cousins has never been tamed or domesticated. Its reputation as a large fierce animal with curvaceous horns made it a favourite target of rich western game hunters who liked to adorn their homes with trophies. The more utilitarian African hunted it for meat and hides.
It is only aggressive if it is under threat. It is therefore wise to keep a safe unobtrusive distance as they are easily spooked. Park rangers on patrol are normally armed in self-defence against them. More people die in Uganda from confrontations with them than any other animal, with the possible exception of the hippopotamus.
Buffalos in the Virungas appear to be smaller, shyer, more nocturnal and move around in smaller herds. The forest species is about half the size of the savannah species; its average height and weight are 120cm/ 4ft and 300kg/660lb. They are generally red-brown in colour with darker and lighter patches that remain in adulthood. In general their horns curve up and back but local variants are also possible.
They are strict herbivores and graze in open grassy areas and on young shoots, saplings and leaves in the open sections of the forest. Closed canopy forest is probably avoided due to a lack of ground vegetation. In common with all other buffalo it needs water daily and never strays far from a reliable water source.
Buffalos can often be found around human areas, if they feel safe. Humans and large carnivores are the most common predators; though their population is controlled more by total food availability than predation. One of their favoured food sources is farm crops and they can devastate a field in no time.
Illustration: Martin Aijuka Depories
The main carnivores in southwestern Uganda are the hyena, jackal, civet, golden cat, honey badger, zorilla, otter, genet and mongoose. Leopards are extinct in Bwindi and possibly in the Virungas, with three other species doubtful.
The side-striped jackal is not a forest species but has adapted to forest life as the wild savannah has disappeared. In terms of habitat preferences, the jackal and African civet live in degraded forest, while palm civet and golden cat stay in mature forest.
Other carnivores can be found in all habitats, although most prefer higher altitudes. Civets, serval cat, Egyptian mongoose and zorilla like the interior. The golden cat, honey badger, and otters hunt nearer to forest peripheries and humans. Mongoose and otters are generalists and are found at forest edges and degraded forest, low altitude grassland and moist habitats.
Most Bwindi carnivores are solitary except for the mongoose and otters. All are opportunists and only the golden cat and otters are specialists in one type – medium sized mammals for the former and fish for the latter. The main prey are monkeys, duikers, bush pigs, goats, civets, rodents, squirrels, birds, zorillas, beetles, bees and molluscs, while all eat some fruit and leaves. Jackals and African civets often raid village refuse piles, standing crops and livestock, particularly goats and poultry.
Photo of a serval cat: Blasio Byekwaso
Once spread all over the continent and the south of Eurasia, leopards (Panthera pardus) are now under attack, especially due to demand for their skins. The coat offers extraordinary camouflage; its colour varies across Africa, with the darkest variations currently found in mountains including Uganda’s Rwenzori Mountains and Ethiopian Highlands.
Females can be up to 140cm/4.6ft tall and weigh between 28 and 60kg (60–130lb). Males can grow to 190cm/6.2ft and 60kg/200lb. They can live up to 20 years.
Leopards are primarily nocturnal. They are solitary and stealthy hunters that feed on diverse prey, mainly found close to the margins of thick cover. Hyraxes, hares, birds, reptiles, fish, monkeys and baboons can be found on their menu, depending on its habitat.
In the Virungas a leopard variant was common, with the last recorded in 1960. In Bwindi they are extinct since 1945–68 but even their previous existence has been doubted by some modern authors. They mainly question the veracity of various sightings as not sufficiently strong enough. It seems strange since the forest is prime leopard habitat with good opportunities for predation. It was the top predator and had no competition for larger prey; the golden cat, the next nearest in size, is hardly more than a metre in length and less than half a metre high.
There is plenty of circumstantial evidence from local Bakiga traditions (the Batwa have never been asked), park rangers, colonial officials and missionaries. In fact missionaries hunted them as a public service to local communities who had problems with rogue animals. In 1928 wounded leopards mauled two missionaries near Gahini, Rwanda; another had a narrow escape from a lion near Lake Edward. It is hardly likely they are all wrong; assuming they were in Bwindi is the only sensible interpretation. There is also a reference to leopards in Echuya circa 1930.
The zorilla is mostly found in open forests and upland savannah but avoids dense forest. Its main diet is rodents, reptiles and invertebrates. It hunts at night. It can either catch prey by stalking and pouncing or excavating them from burrows and hiding places. Prey is killed by repeated deep bites.
Zorillas are noted for their nauseating squirted anal secretions which irritates the eyes and can cause temporary blindness. This defence deters predators and may be used in dominance conﬂicts against other males. The zorilla’s flesh was believed by the Batwa to have strong healing powers particulary for breast diseases of women.
Illustration: Martin Aijuka Depories
There are two species of this antelope found locally, the black fronted duiker and the yellow backed duiker, though the latter is reported to be extinct in the Virungas since the mid 1990s.
They prefer dense forest at all altitudes. They share part of their range with the bushbuck, they often graze together, but duikers are the only species to be found on Mt. Muhavura’s summit (4,127m/1,3500ft).
They live in monogamous pairs in small territories jointly marked and defended against intruders. They are mostly solitary travellers, although some pairs can be seen. High up they avoid rugged terrain and steep slopes, while lower down they avoid areas of human disturbance and are least found near park boundaries (though they like human trails).
They have a high degree of habitat specialisation. What matters is the abundance of food, not the species. In terms of impact they spread fruit seeds but eat young shoots. When together, the duiker’s keener senses help the bushbuck graze longer. They are prey to larger carnivores and humans, and snaring is a major problem. Duikers have always been important nutritionally and economically throughout Africa.
Illustration: Martin Aijuka Depories
Birds are everywhere and can be spotted at all locations, even hotel gardens. The best time to watch them in the highlands is in the morning. They are generally more active during dry weather but the rainy season is when they breed. Breeding seasons are from February to May and September to November. This is when they are most active and the chances of seeing and hearing them increase.
In the Virungas 295 species have been recorded. Sixteen of these are endemic to the Albertine Rift (see the bottom of the page), thirteen of which have been recorded in Mgahinga. Grauer’s swamp warbler is vulnerable to extinction and only lives in three known swamp locations.
In Bwindi there were at least 350 species in the late 1990s of which 184 (53%) were true forest birds. It is a key birding destination in Uganda, significant even on the continental scale. 23 of Uganda’s 24 Albertine Rift endemics can be located in Bwindi. Bwindi has three bird species that are relictual, and the only surviving representatives of their respective genera: African green broadbill, Grauer’s and short-tailed warbler. There are 14 raptors in Bwindi. The most common are crowned hawk eagle, mountain buzzard, rufous-chested sparrowhawk, harrier hawk, spotted eagle owl, long crested eagle and augur buzzard. Others include migratory black kites, nocturnal owls, the secretive bat hawk, Cassin’s hawk eagle, African hobby and steppe buzzard.
Echuya is also an Important Bird Area, with 100 species recorded. There are 43 of 87 highland biome species in the reserve, which include such rare species as the evocatively named handsome francolin, Rwenzori batis, strange weaver and dusky crimson-wing. Others include the Rwenzori turaco, redthroated alethe, Archer’s robin-chat, collared apalis, red-faced woodland-warbler and regal sunbird.
Albertine Rift Endemic Bird Checklist from Rossouw and Sacchi, 1998 (still valid in 2012 according to Nature Uganda)
|African Green Broadbill||✔|
|Kivu Ground Thrush||✔||✔||✔|
|Yellow-eyed Black Flycatcher||✔|
|Red-faced Woodland Warbler||✔||✔||✔||✔|
|Grauer's Rush Warbler||✔||✔|
|Montane Masked Apalis||✔||✔||✔|
|Greater Double-collared Sunbird||✔||✔||✔|
Photo: Blasio Byekwaso
Bees come in two varieties, stingless and honey bees.
Stingless bees are generalists in their selection of nest sites and their main criteria are insulation and low risk of predation. There are about 10 different bee species in Bwindi, with the honey of each having particular medicinal qualities. One species, mostly found in northern Bwindi, nests only on walls. The others nest on trees and one on the ground where it spends one-third of its time. There are usually 1–3 colonies per hectare/2.5 acres. They suffer from habitat loss; fragmentation decreases habitat quality. They don’t like low temperatures, so are vulnerable to seasonal variations. They are most active between 8am-4pm.
The honey bee has larger colonies and more sophisticated communication, is less aggressive and can be attacked by stingless bees. They are bigger, some have developed mandibular teeth, distinct colour and they can recruit rapidly. Their main predators are humans who harvest in parks clandestinely. Other predators are ants, toads, chimpanzees and lizards. It has always been a favoured food of the Batwa who are knowledgeable about the different species and the properties of honey.
Photo: Miha Logar
Butterflies are common and very visible. Their populations fluctuate with the seasons and food availability as they are a measure of an environment’s diversity and health. Butterflies require much additional study.
There are about 1,200 butterfly species in Uganda, mostly in tropical rainforests, and 30,000 worldwide. In Bwindi, there are an estimated 310 species of butterflies from nine separate families – this small area hosts a quarter of Uganda’s species. Little is known about Mgahinga populations. In Echuya there are 54 species of butterflies of which 24 are restricted and seven regional endemics. There are 43 large moths of which four are restricted and one endemic; small moths have not been surveyed.
The maximum diversity of butterflies is in the wet season, peaking in October and April, and minimum in dry seasons, particularly August and February. There are nearly twice as many species in the high months as compared to the low months. In general there are about 15% more males than females.
Photo: Hassan Mutebi