Tragelaphus eurycerus (Ogilby, 1837)

Don E. Wilson & Russell A. Mittermeier, 2011, Bovidae, Handbook of the Mammals of the World – Volume 2 Hoofed Mammals, Barcelona: Lynx Edicions, pp. 444-779 : 608-609

31.

Bongo

Tragelaphus eurycerus

French: Bongo / German: Bongo / Spanish: Bongo

Other common names: Lowland or Western Bongo (eurycerus), Mountain or Eastern Bongo (isaaci)

Taxonomy. Antilope eurycerus [sic] Ogilby, 1837 ,

W Africa.

The Bongo has often been placed in its own genus, Boocercus. Although IUCN and others recognize two subspecies of the Bongo (eurycerus and isaaci), recent univariate and multivariate morphometric analyses failed to demonstrate any consistent separation in geographic samples. Therefore it is considered monotypic here.

Distribution. Two disjunct areas across the lowland rainforest belt of W Africa ( Guinea, Sierra Leone, Liberia, Ivory Coast, Ghana, Togo & Benin) and C Africa through the Congo Basin ( Cameroon, Gabon, Republic of the Congo, DR Congo, Central African Republic & extreme SW Sudan), and five very small disjunct populations in mountainous areas in C Kenya.

Descriptive notes. Head-body 220-235 cm, tail 45-65 cm, shoulder height 122-128 cm; weight 240-405 kg (males) and 210-253 kg (females). The Bongois the largest species in the genus Tragelaphus , with a barrel-shaped torso. Its pelage is striking in color, tone, and pattern. Both sexes are a bright chestnut-red with 10-15 white vertical stripes on the shoulders, sides, and hindquarters, and the number of stripes on each side is often unequal. The Bongo has a chestnut-to-blackish dorsal crest, segmented in white where the stripes meet it. Along with the stripes, both sexes have distinct markings, including a yellowish-white crescent across the chest and two large white spots outlining the jaw on either side of face. The body color of the male Bongo, particularly the head, chest, and shoulders, darkens to blackish with age, and females can become pale with age. Both sexes have brown spectacles around and mostly below the eyes, which remain visible even in old individuals. The legs of both sexes have similar white and black markings just above the hooves, behind the knee joint, and in the pit of the foreleg. The tufted tail is chestnut on the top and whitish underneath. The ears are exceptionally large and broad,likely playing a role in intraspecific signaling and clearly reflecting the importance of hearing in the dense habitats the Bongos occupy. Both sexes have single-spiraled, brownish-black, lyrate horns; with maturity, the tips are ivory-colored due to a lack of pigment. The lengths of the horns are about the same in both sexes (60-100 cm), but male horns are more massive than female horns. Female horns tend to be more parallel to each other, but may be asymmetrical, nearly touching, or even crossing, at the tips. Geographically, male and female skull and horn characteristics tend to be most different in populations that live in more open forest and most alike where they live in dense rainforest. Bongos in Kenya, East Africa, are said to be heavier and taller than those in West Africa. Dental formula is I 0/3,C0/1,P 3/3, M 3/3 (x2) = 32. Diploid numbers for the Bongo are 33 for males and 34 for females, as in the bushbuck group.

Habitat. Bongos occur mainly in disturbed lowland rainforests in West and Central Africa, but the five remnant populations in Kenya are found in montane forests at elevations of 2100-3000 m. Although they spend considerable time moving through and resting in closed-canopy forests, such areas do not provide enough forage to sustain their rather bulky size. Bongos are dependent on lowland forest openings caused by natural, man-made, and even elephant disturbance, and on the open areas at mineral licks, where forage availability is greater than in closed-canopy forests. The proportion of habitats along Bongo travel routes in Dzanga-Ndoki National Park, Central African Republic, were 83% mixed forest, 10% Gilbertiodendron forest, 1-6% forest openings, and less than 0-02% minerallicks. Although minerallicks there are a small percentage of the total habitat used by Bongos, they are visited much more often than would be predicted by their availability, and represent centers of social activity. In mountainous areas in Kenya, the structure of the understory forest vegetation is a key component of Bongo habitat; areas with tall herbaceous vegetation and relatively few woody shrubs are preferred.

Food and Feeding. Herbivorous, but not particularly selective. The Bongo has been traditionally classified as a “browse foliage” specialist, which is largely supported by levels of isotopic carbon in its tissue and diets. In south-western Sudan, Bongos ate the leaves of 116 mostly dicotyledons from the shrub layer in the forest and at its edge; grasses made up only about 10% of the diet in the late dry—early wet seasons. Recent observations, however, suggestit also consumes considerable bulk in grasses and other herbaceous vegetation, particularly at mineral licks. In Dzanga-Ndoki National Park, Bongos ate young leaves of 97 of 138 plant species available to them (vines 45-7%, shrubs 42%, and trees 6-2%) but showed a positive preference for 26 of 100 woody plants. Species of Macaranga, Massularia acuminata, Cleistopholis patens, and Entada gigas were most preferred. Use of fruit and flowers there was limited to only three plant species. Bongos at Dzanga-Ndoki eat substantial amounts of grasses and herbaceous plants that grow in open areas associated with minerallicks, where they also consume mineral-rich soil and drink the muddy water. It is possible that consumption of soil neutralizes effects of toxic chemicals, such as defensive secondary metabolites, that are known to occur in many forest plants. Bongos use their horns to twist and break branches of young trees and tall shrubs to obtain food; they pull down vines to obtain young leaves at the terminal ends.

Breeding. In mountainous areas in Kenya, the birthing and breeding seasons are said to occur in July-September and October—January, respectively. In lowland areas in Central and West Africa, they may be more extended, but little information exists to confirm that. Because Bongos spend most of their time in dense forest cover and are wary, little is known about their breeding behavior in the wild. Minerallicks are places of social interaction, where group sizes are larger. Aggressive interactions and kicking among females suggests a dominance hierarchy, and injuries among mature males, sometimes fatal, suggest at least some vigorous interactions during rut. In captivity, male Bongos display the behaviors typical of bovids, including vulva sniffing, frequent urine-testing of females and subsequentlip curling, and resting the head on the hindquarters of females. Females in captivity tend to ignore the attention of males if they are not in estrus. When females are in estrus, a male assumes a courting low-stretch posture, with his nose up, his neck stretched forward, his horns lying back on his neck, and his tail wagging vigorously; sometimes he flicks his tongue. Displays such as a lateral presentation with the head held high, low-stretch, and thrashing of vegetation have been noted in the wild. Just prior to copulation, a male Bongo assumes a frozen posture behind the female for a minute or so, often looking away from her. If the female is receptive, the male will lick the vulva, brush his cheeks against the female's side, and mount. Unlike females, males are quite vocal during mating, emitting soft clicks, clucks, grunts, and nasal moos. During copulation, which lasts ten seconds or less with up to ten pelvic thrusts, the male extends his chest, neck, and head across the female’s back rather than rising up on his hindlegs. Estrus lasts three days. Gestation is about nine months. In captivity, signs of parturition begin two weeks before the birth. These include swelling of the udder and vulva, distension of the area between the last rib and hindquarters, and sometimes aggressive behavior toward other Bongos. Birth takes place in a lying position. Neonates in captivity are about 19 kg at birth, emit sheep-like bleats, and have similar markings to adults, but are paler. Longevity in the wild is unknown, but captive individuals have lived up to 21 years.

Activity patterns. The Bongo is reported to be mainly nocturnal, with peaks in activity around dawn and dusk. The pronounced patterns and contrast of colors on the Bongo’s coat would be advantageous for social communication under low-light or nocturnal conditions. Bongos rest and ruminate in forest cover during the day from about 10:30 h to 16:00 h. In Dzanga-Ndoku National Park, they rest twice in 24 hours, once at night and once between late morning and early afternoon. Little is know about the specific percentages that Bongos spend in various activities, but they probably follow a typical pattern of alternating bouts of moving/feeding followed by resting/ruminating, usually in forest cover. At tourist lodges in Kenya, Bongos visit established salt licks at night.

Movements, Home range and Social organization. Bongos are non-migratory, but in mountainous areas in Kenya, they move elevationally by the season, spending the damp, misty rainy months dispersed at low elevations and the peak of the dry season in February-March at higher elevations. In Dzanga-Ndoki National Park, mineral licks, most of them created by African Forest Elephants (Loxodonta cyclotis), are focal points of Bongo movements and home ranges. Trails radiate out from regularly visited licks. Forested areas in the Park far from mineral licks are used much less often than forests near mineral licks. While foraging, Bongo groups travel greater average distances between resting places (1-8 km) than individuals travel (0-6 km). Estimated home ranges of two groups of Bongos in Dzanga-Ndoki National Park were 19 km * and 49 km?®. Reported densities range from 0-25 ind/km? in the Central African Republic to 1-2 ind/ km? in south-western Sudan. Bongos are gregarious, and group structureis relatively fluid. Groups of up to 50 can be seen at some mineral licks, but typical group sizes are 2-8 individuals. The largest groups are noted 1-2 months after parturition, when females bring their young out of hiding and the number of young is greatest. Mature males are most likely to be solitary when not engaged in breeding activities.

Status and Conservation. Classified as Near Threatened on The IUCN Red List. Conservation efforts include the establishment of protected areas, particularly in the lowland rainforest of Central Africa, and an attempt to restore Bongo populations in the mountainous regions in Kenya. Overall, Bongo populations are decreasing, and the IUCN/ Antelope Specialist Group considers the mountain populations in Kenya as critically endangered. About 60% of Bongo populations occur in protected areas. Lowland Bongos are thought to number about 28,000, with western populations small and fragmented. The five remnant populations in Kenya number perhaps as many as 140 individuals in one population and as few as six individuals in another. There, restoration efforts have involved moving 18 Bongos from North American zoos to a captive breeding facility at the Mount Kenya Game Ranch in 2004, assessing the suitability of habitats in the region for reintroduction, and establishing genetic monitoring techniques, using feces, to identify individual Bongos and areas of occurrence. Major threats to the Bongo include habitat loss from an expanding human population, international commercial logging and subsequent use of cleared areas for cattle grazing, possible disease transmission from livestock, poaching for bushmeat, and even an increase in the numbers of Lions (Panthera leo) in Kenya. The Bongo is prized by hunters, and regulated trophy hunting could positively affect conservation of the Bongo in lowland forest by generating revenue to support management activities. Restoration of Kenyan populations of Bongo and establishment of more protected areas, particularly in lowland forests where commercial logging threatens some of the highest known Bongo densities, are ongoing priorities of those involved in Bongo conservation.

Bibliography. Bosely et al. (2010), Cerling et al. (2003), Dorst & Dandelot (1978), East (1999), Elkan (1996, 2003), Elkan et al. (2009), Estes, L.D. (2008), Estes, L.D. et al. (2008), Estes, R.D. (1991a, 1991b), Hillman (19864), Hillman & Gwynne (1987), Hofmann & Stewart (1972), Huffman (20040), IUCN/SSC Antelope Specialist Group (2008bf), Jarman (1974), Kingdon (1982), Klaus et al. (1998), Klaus-Hugi et al. (1999, 2000), Leuthold (1977), Lindsey et al. (2006), Melletti et al. (2009), Ralls (1978), Ralls et al. (1985), Rubes et al. (2008), Sayer & Green (1984), Spencer (1995), Spinage (1986), Stanley Price (1969), Weigl (2005), Wilkie & Carpenter (1999).

Figures

18. Western Bushbuck (Tragelaphus scriptus), 19. Central Bushbuck (Tragelaphus phaleratus), 20. Nile Bushbuck (Tragelaphus bor), 21. Lake Tana Bushbuck (Tragelaphus decula), 22. Ethiopian Highlands Bushbuck (Tragelaphus meneliki), 23. Eastern Coastal Bushbuck (Tragelaphus fasciatus), 24. Chobe Bushbuck (Tragelaphus ornatus), 25. Cape Bushbuck (Tragelaphus sylvaticus)

Distribution. Two disjunct areas across the lowland rainforest belt of W Africa ( Guinea , Sierra Leone , Liberia , Ivory Coast , Ghana , Togo & Benin ) and C Africa through the Congo Basin ( Cameroon , Gabon , Republic of the Congo , DR Congo , Central African Republic & extreme SW Sudan ), and five very small disjunct populations in mountainous areas in C Kenya .