The mammalian fauna of Mahale can be loosely classified into three types on the basis of their habitat preferences. The existence of all three types in a single area is unusual and is one of Mahale’s defining characteristics, resulting from the complex mosaic of eco-zones found in the park.
- Tropical rain forest animals, which include chimpanzees (Pan troglodytes schweinfurthii), giant forest squirrel (Protoxerus stangeri), red-legged sun squirrel (Heliosciurus rufobrachium), brush-tailed porcupine (Atherurus sp.), Angolan black-and-white colobus monkeys (Colobus angolensis), bushy-tailed mongoose (Bdeogale crassicauda), banded mongoose (Mungos mungo), blue duiker (Cephalophus monticola) and Sharpe’s grysbok (Raphicerus sharpei);
- Savannah animals, such as lions, Grant’s zebras, warthogs, and giraffes;
- Species found in ‘miombo’ woodland, such as roan antelopes, sable antelopes, and Lichtenstein hartebeest.
A total of 82 species of mammals have now been recorded in Mahale Mountains National Park, which is about 70–80% of the projected total. Of the large mammals, only a handful remain to be found. The latter include greater kudu, southern or mountain reedbuck, and Harvey’s duiker. Some smaller mammals that have not yet been recorded but that almost certainly occur in Mahale include the marsh mongoose, Atilax paludinosus and Smith’s red rock hare, Pronolagus rupestris. By far the greatest number of unrecorded mammals will be bats, rodents and insectivores. Accumulation of new mammal records for the park will probably level out at around 115–120 species.
At least one species of large mammal, the Black rhinoceros, has been extirpated from the park. Although there are no records of this species in Mahale, the local Tongwe people have a name for it, Pela, and it almost certainly occurred in the past.
Long-term Studies of Wild Chimpanzees
Researchers from Kyoto University, Japan, have been studying wild chimpanzees in Mahale since 1965. The distribution of chimpanzees extends from western Africa (Senegal) to central and eastern Africa (Congo, Uganda, Tanzania). West Tanzania represents the most easterly extent of this distribution and it is home to the ‘eastern’ or ‘bald-headed’ subspecies, Pan troglodytes schweinfurthii. The other two sub-species are Pan troglodytes verus and Pan troglodytes troglodytes.
Chimpanzee research depends on habituation of the animals to be studied. This was initially achieved in Mahale by provisioning chimpanzees with sugarcane and bananas, but once good levels of habituation had been established researchers began to decrease the amount of bait, and by 1987 had completely abandoned provisioning. At present researchers are following chimpanzees that range freely in a large patch of forest (30 km²), searching for natural foods. By observing chimps in natural conditions, it has been possible to learn a great deal about their behaviour, ecology and social structure. Some particularly striking discoveries have included the use of tools (e.g., ‘fishing’ for termites using sticks) and medicinal plants, both of which were previously thought to be behaviours attributable only to human beings.
Medicinal Plant Use by Chimpanzees in the Wild
Because chimpanzees are so like us they are often used in laboratory experiments to find cures for human diseases. Field research is now also shedding light on how they cure some of their own diseases in the wild.
Ongoing, long-term field and laboratory studies in Mahale Mountains National Park have produced evidence that chimpanzees infected with roundworms (nematodes) use specific plants to help keep their infections under control, especially during the rainy season. It now appears that some of these plants have a chemical effect (e.g. Vernonia amygdalina) while others have a physical purging effect (e.g. Aspilia mossambicensis). They are used by chimps in different ways, for example:
- Bitter-pith chewing: Chimpanzees carefully remove the leaves and outer bark from young shoots of Vernonia and chew on the exposed pith, sucking out the extremely bitter juice (picture panel). In a few well-documented cases, chimpanzees have been shown to recover their appetites, regain strength, lower parasite loads, and recover from constipation or diarrhoea within 24 hours of using this plant. Interestingly, this species is also used widely across Africa as medicine by many traditional human societies.
- Whole leaf-swallowing: Chimpanzees use their lips to carefully remove one leaf at a time from the Aspilia plant, and pull it into their mouth using their tongue. This causes the rough, hairy leaves to fold up, accordion-style. Each folded leaf is then swallowed whole without being chewed. Leaves are evacuated whole and undigested in their faeces. It has recently been demonstrated that leaves swallowed in this manner physically remove adult worms that were previously attached to the wall of the large intestine. As many as 21 worms have been found trapped within the folds and attached to the surface of these leaves.
The bird species list for Mahale now stands at 355, which represents about 80% of the species that are likely to be found in Mahale. In his field survey, Moyer (2006) noted that the Kabezi area in the north had the highest abundance of birds, but this probably reflects the better visibility in such open woodland habitat, rather than an actual higher abundance of birds. At Kabezi, many records were made of aerial foraging species, birds of prey and migratory species, whereas in the forested study areas (Kasoge and Mfitwa), sight records were a relatively small part of the total and vocal records made up the bulk of contacts. Aerial species may easily be missed when surveying in thick forest, and it can be difficult to detect birds unless they are very close or vocalizing.
Mahale Mountains National Park plays an extremely important role in the conservation of several bird subspecies that are endemic to the immediate area. All endemic taxa at Mahale are classified as ‘Vulnerable’ in the ICBP/IUCN Red Data Book
Reptiles & Amphibians
Very scant information exists about the reptiles and amphibians of Mahale. The Mahale area, and western Tanzania in general, has been very poorly surveyed in the past and much remains to be learnt about the herpetofauna of this area. 26 species of reptiles have been recorded in Mahale, but building up a reasonably complete list is a task that will take many years of focused fieldwork.
In the first systematic study carried out in the park, Moyer (2006) collected twenty species of amphibians. This represents a minimum number for Mahale and the total is likely to be double or triple this figure. Subsequent fieldwork has identified two species (one frog and one gecko) that are likely to be new to science.
Lake Tanganyika is one of the oldest lakes in the world and has several million years of history. About 250 species of fish live in the lake, and most of these are endemic, occurring nowhere else on Earth. The lake is well known for the evolution and adaptive radiation of the Cichlidae family (Perciformes), to which around two thirds of the lake’s fish belong.
Offshore, in abyssal and littoral areas, a variety of complex and stable fish communities have developed. These are largely comprised of Cichlidae species, each of which occupies its own ecological niche, and interacts with others in specific and mutually beneficial ways.
Recently, some interesting aspects of the ecology of these fish have been discovered; for example, the fact that the scale-eating cichlid fish displays ‘mouth-sidedness’. Members of this species belong to one of two morphological types, ‘right-‘ or ‘left-sided’, and their ratio in a population is kept at 1:1 through frequency-dependent natural selection, which is exerted via prey alertness. In other words, if one type of fish becomes more common, prey become better able to detect that morphological type, putting it at a disadvantage, and tipping the balance in favour of the less common type, which subsequently breeds more successfully, and increases in frequency in the population. One cat-fish species provides another interesting example in the form of brood parasitism. Many cichlids keep their fertilized spawn in their mouths until the fry hatch. The fry of one cat-fish species take advantage of this by creeping into the cichlid’s mouth, where they grow whilst eating the fry of their host.
Miombo woodland (dominated by Brachystegia and Julbernardia species) covers about three quarters of the park. This is criss-crossed by narrow strips of riverine forest that grow along some watercourses. Where the mountain chain converges with the lake, there is a broad blanket of lowland forest, known locally as ‘Kasoge’, which extends up to 1 300 m a.s.l. Above this, on the mountain slopes, a mixture of bamboo bushland and montane forest can be found. The montane forest includes trees belonging to genera such as Podocarpus, Bersama, Nuxiacongesta, Macaranga and Croton,which are found in similar forests on Kilimanjaro, Mt. Meru and Ngorongoro. Above 2 300 m the forest gives way to montane grassland. This peculiar habitat mosaic results from the combined presence of Lake Tanganyika and the Mahale Mountains, which affect climatic conditions on a very localized scale.
The total number of plant species recorded in Mahale Mountains National Park is 1174. This list is largely the work of many years of collecting done in the park by the Japanese research team. However, their focus has been on chimpanzee food plants and there remains much general botanical fieldwork to be done in Mahale before the park can be considered well collected. The Albertine rift, an ecoregion which stretches from the northern end of Lake Albert to the southern end of Lake Tanganyika, has a very high number of plant species (5793) and 567 of those are endemic to the region. The current recorded total of 1174 species for Mahale may represent fewer than half of the species actually present there.
The lowland, or Kasoge, forest
Mahale’s lowland forest is found on the western slopes of the Mahale Mountains and along the lakeshore, stretching for 7 km from the Myako Valley to the Lubulungu River. The altitude of this forest ranges from 780 m a.s.l. (lake level) to 1 300 m a.s.l. on the mountain slopes. It covers not only the valleys, but also parts of the ridge. The presence of this forest is due to a suitable local microclimate, which includes higher rainfall than in other parts of the park, and high levels of humidity throughout the year. Such climatic conditions are the result of a humid mass of air over the lake colliding with a cold mass of moving air blowing down from the Mahale Mountains from as high as 2 400 m a.s.l.
The Kasoge forest is an enclave of the central-African, tropical, semi-deciduous forest type. Tall trees belonging to genera such as Canarium, Albizia, Cynometra, Khaya, Xylopia, Pseudospondias, Ficus, Pycnanthus and Garcinia form the canopy of the forest and evergreen vines belonging to Sabaand Landolphia are entwined around these.
Mahale Mountains National Park (1 613 km2) is about 128 km south of Kigoma Town, and forms a peninsula that juts out into Lake Tanganyika. Its centre lies 6°00’ – 6°28’ S and 29°43’ – 30°60’ E.
The western boundary of the park protects not only the lakeshore but also an adjacent 1.6 km-wide strip of Lake Tanganyika’s waters. The Park’s terrain is mostly rugged and hilly, and is dominated by the Mahale Mountains chain that runs from the northwest to the southeast across the park. The highest peak is 2,462 m a.s.l.
There are two seasons in the park. Generally, the dry season starts in mid-May and ends in mid-October with a maximum mean temperature of 31°C. The rainy season lasts from mid-October until mid-May. During both seasons, temperatures can fluctuate, particularly between day and night. The annual rainfall ranges between 1 500 and 2 500 mm.