Tragelaphus sylvestris (Meinertzhagen, 1916)

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 : 606

27.

Nkosi Island Sitatunga

Tragelaphus sylvestris

French: Sitatunga de Nkosi / German: Nkose-Sitatunga / Spanish: Sitatunga de la isla Nkosi

Taxonomy. Limnotragus spekei sylvestris Meinertzhagen, 1916 ,

Nkose [= Nkosi] Island, NW Lake Victoria.

The Nkosi Island Sitatunga was formerly considered a subspecies of T. spekii , butit is diagnostically different from othersitatunga. Monotypic.

Distribution. Apparently endemic to Nkosi I, the southernmost island of the Sesse Archipelago in north-western Lake Victoria. Nkosi I is about 64 km offshore from the Ugandan mainland and about 6 km from its closest neighboring island.

Descriptive notes. Head-body 161-1 cm (male), tail 22:9-23. 5 cm (males); shoulder height 95.3-99. 1 cm (males); weight 96.1-102. 5 kg (males). These measurements come from two males collected on Nkosi Island in 1915 and were published with the original description. Disparity between sizes of male and female Nkosi Island Sitatungas is likely comparable to other sitatunga species. The Nkosi Island Sitatunga is apparently a dryland taxon, and its front and back hooves are a bit shorter (7.3-7. 6 cm vs. 7.6-7. 9 cm) and wider (5.3-5. 9 cm vs. 4.4-5 cm) than those of sitatungas on Bugalla Island in the Sesse Archipelago, and the hooves are distinguished by being “stouter and stronger” (according to the original description). The hooves of a young Nkosi Island Sitatunga captured in 1915 were described as resembling those of a young bushbuck. Males are a uniform dull mouse color, have a paler neck relative to females, the top of their head is reddish, and the preorbital chevron may be faint or distinct. Females are dull red-brown, with a dark dorsal stripe and no white marks. Young are more reddish than females, including the top of the head, with no markings, but there may be banding on the flank, and a paler neck. The ears are large. The skull of both sexes of the Nkosi Island Sitatunga is small, the facial skeleton is very short, and male-only keeled horns are shorter and flare less than the horns of other sitatunga. They spiral 1-5 times and may be whitetipped in mature males. The horns of the two males in the original description were 56.5-59. 1 cm along the total length of the curve, 19-4 cm in diameter at the base, and 17-1-18: 1 cm from tip-to-tip. Dental formula is 10/3, C0/1,P 3/3, M 3/3 (x2) = 32.

Habitat. The only known habitat of the Nkosi Island Sitatunga experienced significant change shortly before the species’ discovery in 1915. By about 1909, the entire Sesse Archipelago was abandoned by humans because of Uganda’s great epidemic ofsleeping sickness (parasitic trypanosomiasis spread by the tsetse fly), and resettlement did not begin until about 1919. In 1913-1915, Nkosi Island was described as completely covered by a dense dry forest with a tangled and dense understory of vines, roots, and fallen trees but little herbaceous ground cover, except for a small opening of grass on its southern end (said to be devoid ofsitatunga tracks). By 1925, after a near 20 year absence of hunting by native peoples, the understory of Nkosi Island lacked foliage from the ground to the height that a sitatunga can reach standing on its hindlegs and the ground cover was nothing but sticks and dead leaves. Individual Nkosi Island Sitatungas at the time were noted to be “mangy” and in poor condition. Nkosi Island is only about 2400 m by 300 m, or 0-72 km?, and results of a drive count along the entire length of the island in 1927 suggested a total population of 150 Nkosi Island Sitatungas, remarkably 208-3/km! It is unlikely that such a density was sustained for long, but unfortunately, no subsequent records can be found.

Food and Feeding. The Nkosi Island Sitatunga was originally described as a browser of leaves, twigs, and bark, given the scant undergrowth available to them. Based on early observations, Nkosi Island Sitatungas foraged at the forest's edge, and the shrub Alchornea cordata was preferred.

Breeding. There is no specific information available for this species, but probably comparable to othersitatunga species.

Activity patterns. Limited early observations of the Nkosi Island Sitatunga suggest a crepuscular activity pattern similar to other sitatunga species. Like other ruminants, activity is no doubt an alternating pattern of feeding and ruminating/resting.

Movements, Home range and Social organization. There is no specific information available for this species, but individuals on Nkosi Island probably move throughout the entire 0-72 km*island and are more gregarious than other sitatunga species out of necessity. The Nkosi Island Sitatunga wasinitially described as quiet, not vocalizing with the typical staccato bark of sitatungas on other Sesse islands. There are no known predators of the Nkosi Island Sitatunga.

Status and Conservation. Classified as Least Concern on The IUCN Red List (under T. spekii ), which does not differentiate the five species identified here. Sitatunga occur on other islands of the Sesse Archipelago. They were originally described as disparate from the Nkosi Island Sitatunga, but anecdotal reports, mostly from hunting outfitters, suggest that all sitatungas in the Archipelago are different from the mainland form, the Lake Victoria Sitatunga (7. spekii ). Future research will be required to clarify the extent of the range of the Nkosi Island Sitatunga and its particular conservation challenges as an island endemic.

Bibliography. Ansell (1972), Bro-Jorgensen (2008), Carpenter (1925, 1929, 1934), East (1999), Fiske (1920), Groves & Grubb (2011), Huffman (2004q), IUCN/SSC Antelope Specialist Group (2008bi), Kingdon (1982, 1997), Meinertzhagen (1916), Pitman (1929).

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. Apparently endemic to Nkosi I, the southernmost island of the Sesse Archipelago in north-western Lake Victoria. Nkosi I is about 64 km offshore from the Ugandan mainland and about 6 km from its closest neighboring island.