Tragelaphus decula (Ruppell, 1835)

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 : 599

21.

Lake Tana Bushbuck

Tragelaphus decula

French: Guib decula / German: Athiopien-Schirrantilope / Spanish: Bushbuck del Tana

Taxonomy. Antilope decula Ruppell, 1835 ,

Abyssinia, W Ethiopia.

The Lake Tana Bushbuck was formerly considered a subspecies of T. scriptus , but diagnostically different from other bushbucks. The Lake Tana Bushbuck is a mountain endemic and evidently a species of hybrid origin because it has the phenotype of the sylvaticus group but the mtDNA of the scriptus group. Synonyms of the Lake Tana Bushbuck include multicolor , nigrinotatis , and fulvo-ochraceus . Monotypic.

Distribution. Mainly in lowland Ethiopia but also likely in S Eritrea, SW Djibouti, and extreme SE Sudan.

Descriptive notes. Head—body 117-145 cm (males) and 114-132 cm (females), tail 19-24 cm, shoulder height 64-100 cm (males) and 61-85 cm (females); weight 40-80 kg (males) and 24-60 kg (females). These measurements are general for the bushbuck group and should be considered provisional until further information is available for individual species. Tragelaphines are typified by their sexual dimorphism, and the weight of male bushbucks, in general, is about 160% of that of females. Bushbucks are the smallest tragelaphines, with large ears and eyes and a rather round, crested back. Their hindquarters tend to be higher and more robust than their forequarters. The color of both sexes of the Lake Tana Bushbuck is ocher to yellowor sandy-brown, often with a dark suffusion of the hairs on the back and a black dorsal crest. The white markings typical of the Western Bushbuck (7. scriptus ) are indistinct on the Lake Tana Bushbuck, fading completely in old animals, with the exception of some haunch spots and two white spots, one below the eye and the other on the lower jaw. Two longitudinal bands are often visible in young animals. Both sexes have a fully haired neck, a white throat-patch, and sometimes a white breast-patch. The fronts of forelegs are black, with white on the fronts of the knees. Inguinal glands occur ahead of the mammae, but there are no false hoof glands. Tails are relatively short, long-haired, and bushy, dorsally colored the same as the back, white underneath, and usually tipped in black. Only males have keeled horns, which are nearly straight with generally only one or slightly more twists. The average length of the horns of the Lake Tana Bushbuck is about 25 cm. Average total length of the skull is 22-3 cm. Dental formula is I 0/3, Co0/1,P 3/3, M 3/3 (x2) = 32. Diploid numbers for the bushbuck group are 33 for males and 34 for females.

Habitat. As a group, bushbucks are the most ubiquitous hoofed mammals in Africa, but because of their relatively solitary nature (particularly males), relatively small size, tendency to freeze and cryptically blend into their surroundings, and preference for forest and forest edge, they are difficult to observe and census. According to Y. Moodley and M. W. Bruford, the Eritrean Sahellian Acacia Savanna and the Somali Acacia Commaphora Brushland and Thicket ecoregions are occupied exclusively by the Lake Tana Bushbuck haplogroup. They are usually found near free water, which may be as much a reflection of their preferred forested habitats thriving near water as a physiological need.

Food and Feeding. There is no specific information available for this species, but probably, like other bushbuck species it eats a variety of shrubs, legumes, and other herbaceous plants as well as new-growth of grasses. Bushbucks are fond of the fruits of various trees and can be observed feeding on fallen fruits under trees in which baboons and other monkeys are foraging. In various locations, bushbucks are agricultural pests, eating various crops by night.

Breeding. Bushbucks have been described as the most socially primitive of the tragelaphines and are typically thought of as non-terrritorial polygynous breeders (see the Nile Bushbuck for the most thorough studies of breeding behavior).

Activity patterns. Few specifics have been reported for the Lake Tana Bushbuck, but activity patterns are probably comparable to the general bushbuck pattern; crepuscular and nocturnal, spending much of the day resting/ruminating in forest cover, often alone or mother—offspring pairs.

Movements, Home range and Social organization. There is little specific information available for this species, but it is probably comparable to other bushbuck species (see the Nile Bushbuck for the most through studies of these characteristics). Bushbucks do not range over a wide area. Home ranges are not exclusive, but individuals do have their own, apparently exclusive, places to rest during the day. Although not aggressive to one another, regular social interactions among bushbucks are largely confined to mother—offspring pairs and male—females during rut.

Status and Conservation. Classified as Least Concern on The IUCN Red List (under 7. scriptus ), which does not differentiate the eight species identified here. Some localized populations of bushbucks have decreased because of excessive illegal harvest, destruction of native habitats as human populations and livestock numbers have increased, and increased aridity. Generally, however, bushbucks can do well in areas of human habitation because of their secretive nature, non-herding tendencies, cryptic coat patterning and tendency to freeze and blend into their surroundings when faced with danger, and flexible daily schedules, adopting a nocturnal pattern in areas of human activity. Bushbuck populations are considered stable range-wide. The Lake Tana Bushbuckis one of the least known of the bushbuck species, so future research is required to establish its population characteristics and conservation needs.

Bibliography. Ansell (1972), Bro-Jorgensen (2008), East (1999), Estes (1991a, 1991b), Groves & Grubb (2011), IUCN/SSC Antelope Specialist Group (2009), Kingdon (1982, 1997), Lydekker & Blaine (1914), Moodley & Bruford (2007), Moodley et al. (2009), Nowak (1999), Olson et al. (2001), Walther (1990a), Wronski & Moodley (2009).

Figures

14. Saola (Pseudoryx nghetinhensis), 16. Chowsingha (Tetracerus quadricornis), 17. Nyala (Nyala angasii)

Distribution. Mainly in lowland Ethiopia but also likely in S Eritrea , SW Djibouti , and extreme SE Sudan .