By J du P Bothma

The relatively little known bongo Tragelaphus eurycerus is the largest forest-dwelling antelope in Africa and only occurs in rainforests. It is a spiral-horned antelope and the generic name Tragelaphus is derived from the Greek words tragos for a male goat and elaphos for a deer. The specific epithet eurycerus is derived from the Latin words eurus for wide and keras for horn. The scientific name therefore reflects the wide, spiralled horns of both sexes. Fossils of the Tribe Tragelaphini that are some
4 million years old are only found in Africa, among others at Omo in Ethiopia. This indicates an African origin.

Tragelaphus eurycerus eurycerus of West Africa and Tragelaphus eurycerus isaaci of the Aberdare Range and foothills of Mount Kenya in East Africa were once regarded as separate subspecies. However, they are now regarded as ecotypes and no longer as subspecies. The western ecotype is commonly known as the western or lowland bongo and the eastern one as the eastern or mountain bongo. The bongo was originally described as Boocerus eurycerus by Ogilby in 1837. The generic name Tragelaphus was coined by De Blainville in 1816 for a group of spiral-horned antelope, and the bongo was renamed as a member of the genus Tragelaphus by Thomas in 1902.

The bongo is the largest and most colourful of the antelopes of the African forests, with those from the Aberdare Range and the foothills of Mount Kenya in East Africa having a more vibrantly coloured coat than those further west. Like the nyala Tragelaphus angasii the bongo shows sexual dimorphism in coat colour although the adult bull and cow are similar in size with a shoulder height of some 1,2 to 1,3 m. However, an adult bull weighs 240 to 405 kg, as opposed to 210 to 235 kg of an adult cow. The eastern ecotype is larger and heavier than the western one.
The coat colour of an adult cow and a young bongo is chestnut red with darker red legs, while the auburn to chestnut red coat of a young bull darkens with age to eventually become dark brownish-black. Both sexes have 10 to 15 whitish-yellow stripes over the trunk of the body and the rump and these stripes are more striking in the eastern bongo. The stripes serve as camouflage to avoid predators in the forest environment. The legs are short relative to those of any other African antelope and this helps bongos to move rapidly through dense forests. The large ears improve hearing in the closed forest environment, and there are black and white markings on the face and legs. The lips are white and topped by a black muzzle. As in other species of Tragelaphus, there is a white chevron stripe between the eyes. There is another white chevron where the neck meets the chest, two white spots on each cheek and a short, bristly, vertical brown ridge of hair which forms a crest along the spine from the shoulder to the rump. There are no special secretion glands as scent is a relatively unreliable form of communication in a dense forest.

The bongo resembles the eland in that both sexes have spiralled horns, which in the bongo are lyre-shaped, slope backwards and are covered by a keratinous, blackish-brown sheath. When in flight, the horns are laid onto the back to prevent them from impeding the animal’s movement through dense forest. However, in the cow the horns only make one full turn and are more parallel and slender than in the bull, where the horns of older animals become robust and develop up to 1,5 turns. The coat colour pigmentation rubs off easily.

Historically, the bongo occurred in three disjunctive regions in eastern, central and western Africa but they now primarily occur from the dense, lowland forests of West Africa and Zaire to southern Sudan, with small and isolated populations in the forests of the highlands of Kenya and in the Congo.

The preferred habitat is disturbed mosaics in rainforests with fresh green vegetation, such as ground-level bushes and shrubs. In the mountainous forests of East Africa, however, they occur in dense bamboo and broad-leaved forests.

The bongo is the only forest antelope with a complex social system. In the bongo, this system includes breeding herds consisting of a few adult bulls and 6 to 50, but seldom more than 20, adult cows and young animals. Most of the adult bulls are solitary in habit, and nursery herds of calves are formed. The bongo is active by day and night with a peak of activity around midnight and again just before sunrise. It stays in the forest during the day and only comes into the open to visit salt licks at night. Bongos are inactive in the middle of the day and also stop feeding and move into shelter when it rains heavily. The range size of a breeding herd depends on the habitat quality and varies from 120 to 300 km2. In the mountainous regions of East Africa the bongo moves to the lower footslopes in the wet season.
A bull becomes sexually mature at around 30 months of age and a female at 27 months. Little is known about reproduction in the wild but mating seems to peak from April to November in someareas. A single calf weighing about 19,5 kg is born in a traditional calving ground after a gestation period of some 9 months. The calf remains hidden for the first few weeks of life

and twins are known to occur occasionally. A calf grows rapidly; the horn buds appear when it is some 3,5 months old and it becomes mobile when it is 2 to 3 months old. Weaning occurs at an age of 6 months and longevity can be as much as 21,5 years.
Bongos are susceptible to diseases such as rinderpest, which almost exterminated them in the 1880s. They also suffer from goitre problems after being exposed to goitrogen, which occurs in some food plants, including the bamboo and some cereals. This substance suppresses the function of the thyroid gland by interfering with the uptake of iodine and may be one reason why the bongo utilises mineral licks. Leopards and spotted hyenas are the bongo’s natural predators, while pythons occasionally kill the calves.

The bongo is a mixed feeder that requires highly nutritious, green herbage. It feeds in disturbed forest parts on the leaves of trees, bushes, creepers and vines, and on bamboo shoots, wild flowers, bark, the pith of rotten trees, grasses, herbs and roots. It will also enter cultivated fields to feed on cereals. Salt is an important nutritional requirement and the animal will regularly visit natural salt licks. It will eat the charcoal of woody plants that have been burned after being struck by lightning for the mineral content, as does the okapi. The bongo requires an ample supply of food and is therefore restricted by its food requirements to areas that contain an abundance of low shrubs and herbaceous plants that are high in protein and low in fibre content throughout the year. Such food in part defines the habitat choice of a bongo. When feeding, a bongo uses its long, prehensile tongue to grasp leaves and its broad horns to pull down and break branches. The availability of a permanent water source is crucial for habitat to be suitable for the bongo.

Human pressure on the habitat is threatening the survival of the bongo and there is a programme underway by the Association of Zoos and Aquariums to improve the genetic diversity of managed bongo populations. There also is a formal Bongo Surveillance Programme in Kenya, while the protection of populations in suitable habitats is paramount. The bongo forms part of the bushmeat industry in West Africa and humans utilise the vivid pelts, large horns and meat as trade goods.

Little information on the capture of bongos is available although the use of licks may make passive capture possible. The use of regular trails may also make the use of capture nets possible, while bongos are apparently easy to catch in snares.

Stocking density
The stocking density will depend on the habitat quality and can range from one bongo per 4 km2 in optimal habitats to as low as one bongo per 50 km2 or more elsewhere.

Meat and live sales
The bongo is too rare to be utilised as a legal source of meat although it will probably yield a carcass of around 55 per cent of its live weight. It is not being sold on live wildlife auctions in South Africa.

Trophy hunting can potentially provide economic justification for the preservation of areas of bongo habitat that are larger than those that are available in the current national parks, especially in the more remote regions of Central Africa where commercial tourism possibilities are limited. Some known trophy records include the following:
• Rowland Ward:
Minimum horn length: 27,000 inches (68,580 cm); best: 36,125 inches (91,758 cm) and held by PH Flack.
• Safari Club International:
Minimum horn points: 83,375; best: 97,500 points and held by
Bill H Clark.
• South African Method:
Minimum horn length: 27,000 inches (68,580 cm); best: 36,1875 inches (91,916 cm) and held by MH Viljoen. ASM

Selected sources
Anon. 2013. Bongo (antelope).
Brensike, J. 2012. Tragelaphus eurycerus bongo.
Grubb, P. 2005. Order Artiodactyla. In: DE Wilson & DM Reeder (Eds), Mammal species of the world, third edition. Baltimore: Johns Hopkins University Press, pp 697–698.
Kingdon, J. 1982. East African mammals, Volume IIIC revised. Chicago: University of Chicago Press, pp 142–157.
Photos: AfriPics and Africa Imagery