Tragelaphus gratus, Sclater, 1880

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 : 606-607

29.

Western Sitatunga

Tragelaphus gratus

French: Sitatunga du Gabon / German: Westliche Sitatunga / Spanish: Sitatunga occidental

Other common names: \\ Vestern Marsh Buck

Taxonomy. Tragelaphus gratus Sclater, 1880 ,

Gabon.

The Western Sitatunga was formerly considered a subspecies of T. spekii , but it is diagnostically different from other sitatunga. The new separation of T. spekii into five species, each with its own nomenclatural history, makes demarcation of current ranges difficult. Monotypic.

Distribution. Discontinuous and limited to wetland environments in the Congo Basin N and W of the range of the Zambezi Sitatunga in S Benin (Porto Novo), S Nigeria, Cameroon, Central African Republic, Equatorial Guinea, Gabon, Republic of the Congo, N DR Congo; also several isolated populations in W Africa ( Senegal, Gambia & Guinea-Bissau), NE Nigeria and W Chad, and perhaps extreme S Ghana. Maps and distributional information here are provisional pending future research.

Descriptive notes. Head-body 152-163 cm (males) and 123-127 cm (females), tail 24-43 cm, shoulder height 89-97 cm (males) and 75-84 cm (females). No specific weights are available, but the Western Sitatunga is thought by some to be the heaviest of the sitatunga species. Sitatungas are among the most sexually dimorphic tragelaphines, with mass of males as much as 170% of the mass of females. The hooves of all but the Nkosi Island Sitatunga (7. sylvestris ) are very elongated, with flexible toe joints and large false hooves, which help prevent them from sinking into the mud and vegetation mats of their preferred swampy habitats but make them clumsy on dryland. Their pelage tends to be shaggy, oily, and water-repellent, and males develop a scraggly mane as they age. The Western Sitatungais relatively large, and its coat coloris generally pale pink-brown; both sexes have a white dorsal crest, with white lateral stripes and rump spots. A female from Mbi Crater, 15 miles north-east of Bamenda, Cameroon, was a dull gray-yellow brown with four very faint stripes, but her white dorsal stripe was very clear. A male from Tiko, in western Cameroon, was a rich pale rufous; he had spots high on his back rather than stripes, and a clear black dorsal stripe. The skull,if the Cameroon sample was typical, was somewhat like that of the Nile Sitatunga, but he had very short horns. Male-only keeled horns are spiraled 1-5 times and average about 51 cm in length in a sample from Cameroon. Dental formulas 10/3, C0/1, P 3/3, M3/3 (2) = 32

Habitat. Sitatungas as a group, except the Nkosi Island Sitatunga, are described as semi-aquatic, limiting most of their activities to the swamps, bogs, and marshes associated with rivers, streams, lakes, and lowland forests of poor drainage that are scattered intermittently throughout their range. They are excellent swimmers and will avoid danger by escaping to deep water, and are capable of submerging their entire body with little more than their nostrils above the surface. In central Gabon, most sightings of the Western Sitatunga were made in narrow gallery forests along watercourses. In Abuko Nature Reserve in Gambia, observations of Western Sitatungas suggested broader habitat choices: 32:9% of the observations were in swampy habitat, 28:4% in clearings, 20-6% in savanna, and 18-1% in riverine forests.

Food and Feeding. Herbivorous and generally thought to be intermediate feeders. In Abuko Nature Reserve in Gambia, Western Sitatungas ate parts of 21 different plants (leaves, flowers, fruits, and vine stems) from 17 plant species. During those feeding observations, Western Sitatungas ate plants in savanna habitats (39-4% of the time), swamps (33:3%), clearings (24:2%), and riverine forests (3:1%). These observations suggest greater habitat flexibility than normally afforded the sitatunga group, which is generally thought of as swamp-obligate. On the other hand, swamp habitatis relatively uncommon at Abuko, and pools associated with them contain significant numbers of Nile crocodiles (Crocodylus niloticus). In the Republic of the Congo, Western Sitatungas are partial to two seed types found in the dung of African Forest Elephants (Loxodonta cyclotis). In Gabon, they have been described as nearly obligate leaf eaters.

Breeding. The breeding behavior of the Western Sitatunga has been described in detail only at two locations, and they were remarkably different. In a small introduced population in Abuko Nature Reserve, Gambia, normally solitary males and females basically only interact during breeding in April-July. A male courts an estrous female attentively, following her closely, mewing, regularly testing her urine, and subsequently displaying the classic ungulate lip curl. Young and mature males regularly horn the ground and vegetation. One case in Gambia suggested that a mature male died as a result of two deep puncture wounds incurred during a fight with another male. Offspring in Gambia are born in October—]January after a purported gestation of about seven months. They may remain hidden for up to seven weeks. One known female there produced four offspring every year from early 1979 to December 1982. In sharp contrast, a large, cohesive group of Western Sitatungas in Odzala National Park, Republic of the Congo, occupied a single forest swamp clearing over 3-5 years of observation. The group functioned like a harem, with gregarious adult females and a single mature male that did all the breeding. All young male and some young female offspring born during the period of observation left the group. Breeding was not seasonal, and the 28 births observed occurred throughout the year, with birth intervals of 5-5-9 months. In contrast to Gambia, gestation in Odzala National Park was reported to be only 5-5 months. Neonates were kept hidden for two weeks, and weaning occurred after about four months. First breeding of females did not occur until 2-2-5 years of age. Despite differences between the two locations, male and female offspring separated from their mothers at about 8-9 months old. The observations in Gambia are the most typical breeding models of sitatunga species reported in the literature, and the Odzala National Park case was hypothesized to be related to a stable and perennial forage base and mineral resources in the forest swamp clearing. The vegetation there never dried out and was always succulent, nutritious, and available, affording the opportunity for this rather aberrant breeding model, described as “female-defense polygyny.” Western Sitatungas can live up to almost 23 years in captivity, probably about twelve years in the wild.

Activity patterns. Feeding by Western Sitatungas in Gambia was most commonly observed from 06:00 h to 08:00 h and from 17:00 h to 19:15 h, and they rested/ruminated under palms, in dense vine thickets, or in the swamps for most of the other daylight hours.

Movements, Home range and Social organization. As a group, sitatungas are not very gregarious, and most observations suggest that adults occur alone except during breeding. The average group size of the Western Sitatunga in natural rainforest fragments in central Gabon was one, and densities were only 0-3 ind/km?, no doubt dependent on the availability of marshy habitats. In Abuko Nature Reserve, Gambia, 63-9% of all observations of the Western Sitatunga were single individuals, and 26-5% were of a mother and her offspring. In contrast, a large stable group of 16-36 Western Sitatunga used a forest swamp clearing in Odzala National Park, Republic of the Congo, by day, but it broke up into subgroups that averaged 2-5 individuals by night (34-3% of those subgroups were a mother and her offspring). Although a small part of their diet, Leopards (Panthera pardus) have been known to prey on the Western Sitatunga during the dry season in Lopé National Park, Gabon.

Status and Conservation. Classified as Least Concern on The IUCN Red List (under 7. spekii ), which does not differentiate the five species identified here. Generally, numbers of sitatungas are stable in areas of low human population density and decreasing elsewhere. As many as 170,000 sitatungas may occur discontinuously throughout the group’s range in Africa, with about 40% living in protected areas. That number, however,1s considered an overestimate, and local populations are threatened by loss of habitat, altered hydrology of their critical wetland habitats, livestock grazing and likely associated disease transmission, uncontrolled burning of swampland, and overharvest for subsistence and the bushmeat trade. Increased roads and associated hunting pressure are associated with decreased abundance of the Western Sitatunga in southern Gabon, but it can survive in close proximity to human settlements if protective wetlands allow refuge from hunters; under such circumstances, it becomes totally nocturnal. Hunters involved in the illegal bushmeat trade to local and bigger city markets and logging towns in the Central African Republic, Cameroon, Equatorial Guinea, and elsewhere often use cable snares along trails in reed swamps that are particularly focused on the Western Sitatunga. In the late 1990s, the Western Sitatunga was still common in Monte Alen National Park, Equatorial Guinea, but it was considered rare and decreasing in Gambia and Senegal. Minimizing loss of wetland habitats and,critically, their interconnectedness, which minimizes isolation and permits dispersal and gene flow, is fundamental to the long-term conservation of all sitatungas, including the Western Sitatunga.

Bibliography. Angelici et al. (2001), Ansell (1972), Bro-Jorgensen (2008), Cotton (1935), East (1999), Estes (1991a, 1991b), Gautier-Hion et al. (1980), Groves & Grubb (2011), Henschel et al. (2005), Huffman (2004q), IUCN/SSC Antelope Specialist Group (2008bi), Kingdon (1982, 1997), Laurance et al. (2006), Lydekker & Blaine (1914), Magilocca et al. (2002), Noss (1998a, 1998b), Nowak (1999), Sayer & Green (1984), Sclater (1880), Starin (2000), Tieguhong & Zwolinski (2009), Tutin et al. (1997), van Vliet & Nasi (2008), Walther (1964), Weigl| (2005).

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. Discontinuous and limited to wetland environments in the Congo Basin N and W of the range of the Zambezi Sitatunga in S Benin (Porto Novo), S Nigeria , Cameroon , Central African Republic , Equatorial Guinea , Gabon , Republic of the Congo , N DR Congo ; also several isolated populations in W Africa ( Senegal , Gambia & Guinea-Bissau ), NE Nigeria and W Chad , and perhaps extreme S Ghana . Maps and distributional information here are provisional pending future research.