Kobus defassa (Rüppel, 1835)
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publication ID |
https://doi.org/ 10.5281/zenodo.6512484 |
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DOI |
https://doi.org/10.5281/zenodo.6636846 |
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persistent identifier |
https://treatment.plazi.org/id/03F50713-9909-FFB3-037D-F9F2FB63F941 |
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Conny |
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scientific name |
Kobus defassa |
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Defassa Waterbuck
French: Cobe defassa / German: Defassa-Wasserbock / Spanish: Kob acuético septentrional
Other common names: Sing-sing Waterbuck
Taxonomy. Antilope defassa Ruppell, 1835 ,
Near Lake Tana, Abyssinia.
The Defassa Waterbuck was formerly included as a subspecies of K. ellipsiprymnus .
However, microsatellite analysis shows significant differentiation between these two waterbuck groups. Hybridization has been observed in regions of sympatry (e.g. Nairobi National Park and Samburu National Park, Kenya), resulting in intermediate phenotypes, although genetic introgression appears to be limited. Numerous subspecies belonging to the Defassa Waterbuck group have been described based on morphological differences, but significant variation may also exist between individuals within a population. Pending further review, this species is considered monotypic here.
Distribution. From Senegal and Gambia to N Ethiopia and Eritrea, and S to Zambia;; isolated populations exist in S Gabon, W Republic of the Congo, and Angola. The Rift Valley in C Kenya and C Tanzania forms the E distributionallimit; distribution to the S is restricted by the Muchinga escarpment in Zambia. View Figure
Descriptive notes. Head-body 175-235 cm, tail 33-40 cm, shoulder height 120-136 cm; weight from Ugandan specimens: 198-262 kg (males) and 161-214 kg (females). The pelage of the Defassa Waterbuck is coarse and shaggy, particularly on the neck. Glandular secretions give the hair an oily feel and a “sweet and musky” odor. Coat coloris generally reddish-gray. Individual variation may range from bright rufous to grizzled gray, but Defassa Waterbucks are generally redder than Ellipsen Waterbucks ( K. ellipsiprymnus ). The underparts and inner surfaces of the legs vary from white to dusky brown. In contrast to the Ellipsen Waterbuck, the rump is entirely white, and this rump patch does not extend above the base of the tail. The legs are dark, and a narrow white band is present above the hooves. The forehead is often bright rufous, and a distinct brownish-black blaze extends along the bridge of the nose from the eyes to the nose. White superciliary stripes, markings around the nose and lips, and a bib on the upper throat are similar to those seen in the Ellipsen Waterbuck. The ears are short and rounded; the inner surfaces are covered with tracts of white hair in individually distinct patterns. Aside from their largersize, males are readily distinguished from females by the presence of horns. The horns extend backward from the forehead and then curve upward; when viewed from the front, they diverge at their bases, becoming increasingly parallel (and sometimes converging slightly) toward the tips. Horn length in mature males is 75-84 cm. Dental formulais10/3,C0/1,P 3/3, M 3/3 (x2) = 32.
Habitat. The Defassa Waterbuck is most common in grasslands, although open forest and scrub habitats are also used. Adult females show greater use of open forest compared to adult males, which primarily inhabit open grassland. Savannas dominated by Heteropogon contortus and Hyparrheniafilipendula are generally preferred; open forests of Capparis tomentosa and Euphorbia candelabrum are favored over other tree communities in Uganda. The Defassa Waterbuck is always found within a few kilometers of water, and even arid zones may be colonized if a water source is nearby. Unlike many other Kobus antelopes, the Defassa Waterbuck does not use wateras a refuge from predators, fleeing into dense brush instead. Dense forests are avoided. Population densities vary widely with habitat type and region. Very high densities, averaging 30 ind/km?, were formerly recorded around Lake Nakuru in Kenya; local densities in this region were as high as 100 ind/km?. Current estimates for this region are lower, butstill exceed an average of 10 ind/km? This species is considered common in parts of Uganda, where densities average 2-1 ind/km? but can be as high as 10-9-17-7 ind/km? in localized areas. Densities are much lower in West Africa: 0-4 ind/km? in Senegal and 0-02-0-21 ind/km? in Comoé National Park, Ivory Coast.
Food and Feeding. The Defassa Waterbuck is primarily a grazer, although the diet fluctuates throughout the year to make use of available greenery. The flush of growth associated with rain results in a diversification of plants consumed. Annual grasses comprise over 50% of plants in the diet during the rainy season in Benin. In drier periods, the diet becomes increasingly restricted; perennial grasses increase in importance (to over 50% of the diet) and leaves may be browsed from trees (up to 35% of diet in Benin, but much less in southern regions). Frequently consumed grasses in the eastern and southern parts of the Defassa Waterbuck’s range include Aristida spp., Bothriochloa spp., Brachiaria spp., Chloris spp., Cynodon dactylon, Digitaria spp., Heteropogon contortus, Hyparrhenia filipendula, Panicum spp., Sporobolus pyramidalis, and Themeda triandra. In Benin, the grasses Panicum anabaptistum, Echinochloa stagnina, and Andropogon gayanus are consumed year-round. Adult females and territorial males feed in prime habitats; bachelor males, which are excluded, must forage on more marginal resources. Unlike the Ellipsen Waterbuck, the Defassa Waterbuck will not wade into inundated grasslands to feed. However, this species needs to drink regularly and may travel over 1-5 km between grazing areas and water sources during the dry season.
Breeding. Breeds throughout the year. Peaks in birth rates are generally correlated with rainy seasons, and thus vary between regions: in Kenya, most births occur between July and January (particularly December—January); in Uganda, birth peaks occur in March-April and October-November; and in Zambia, they are largely confined to November—April with a distinct peak in late January. A male courts an estrous female by following her while champing his lips; if the female stops and urinates, the male lets the urine flow over his nose and mouth, then performs flehming by curling the lips distinctively. Mounting is presaged by gentle kicks of the male’s forelegs directed between the hndlegs to the abdomen of the female (“laufschlag”). Full estrus may last for 18 hours and numerous copulations (up to nine recorded) may occur; successive copulations are generally with the same male, but on occasion multiple partners are involved. The moment of ejaculation is marked by a slight jump: the hindfeet of the male are off the ground for a fraction of a second. Gestation has been estimated at approximately 240 days, although captive observations suggest thatthis is an underestimate;six reported values range from 272 days to 287 days. Litter size is typically one, although infants may associate together, leading to unsubstantiated reports of twinning. A single full-term fetus weighed 14-2 kg. Neonates are hidden in dense vegetation, usually a thicket or woodland, by their mothers for 2-4 weeks. During this time, the mother remains within a few hundred meters, visiting sporadically throughout the day and night to suckle the infant. Young animals are recognizable by their short, fluffy coat, which they retain until weaning at 6-8 months of age. Females begin to mature sexually at two years of age, and are generally fully mature at three years. The development of males is more protracted. They typically disperse from their mothers by eleven months and join a bachelor group. Puberty begins at two years of age; full spermatogenesis occurs by four years of age and testicular development plateaus at b—6 years. By the sixth year, full adult size and horn length have been reached, at which point males begin to establish territories. Average life span of males in the wild is eleven years. Females generally live for 13 years (although an individual 18-5 years old was observed in the wild); in captivity, one female lived to 23 years and four months.
Activity patterns. Defassa Waterbucks may be active throughout the day and night. During daylight hours, there are peaks in activity (feeding and moving) in the morning and evening, although foraging may occur at all hours of the day. Resting increases with higher solar radiation; the greatest proportion of resting occurs between 10:00 h and 14:00 h, with a peak at 13:00-14:00 h. On average, 37% of daylight hours are spent feeding, 15-5% standing, 37-8% lying, and 6-7% walking; the remainder is accounted for by other less frequent behaviors such as grooming and sexual activity. Females spend significantly more time foraging than males (38-4 vs. 26:4%), at the expense of resting. Conversely, bachelor males spend significantly more time lying down (51-7%), which is thought to correspond with increased rumination due to lower quality food intake. Midday rests and overnight periods are often spent in wooded areas; foraging generally occurs in open grasslands. Daily movements rarely exceed 1 km. Limited nocturnal observations of males indicate that foraging occursless frequently at night, peaking between 24:00 h and 02:00 h. Much of the night is spent ruminating, and little time is spent resting or sleeping. Deep sleep is rare and lasts for 4-6 minutes when it occurs.
Movements, Home range and Social organization. The social system of the Defassa Waterbuck has been well documented, particularly in Uganda. Females live in small maternal groups that frequently change in size and composition; associations between individuals are temporary (no long-lasting social bonds have been observed). Female group size is smallest (3-6 individuals) during the rains; as populations condense around water sources in the dry seasons, associations may number up to 25 animals. Home ranges of individual females are approximately 6 km? although movements are confined to a smaller area at the peak of drought conditions. Male home ranges are generally less than 1-5 km? and thus a female’s range overlaps those of several males. Mature males are generally territorial, although in high-density populations only a fraction of them (as little as 7%) may be able to maintain a territory at any given time. Territories are defended year-round against other territorial males, but non-territorial males may be tolerated during parts of the year (such as the late dry season in Zambia) and are only forcibly excluded during the breeding season. Thesize of each defended area varies between 0-04 km?and 1-5 km? (averaging 0-8 km?); the largest territories are maintained by prime males between seven and nine years of age. Males often defend shorelines of lakes or rivers, and are thus able to attract females due to constant access to green vegetation. Females are herded away from territory borders, but these actions are rarely successful in preventing females from leaving. Territorial boundaries are not marked, but they are maintained using visual displays between neighbors. Lateral displays with the head held high andtail stiffly horizontal occur frequently, as do horn displays, where the ground may be dug up or bushes thrashed. Such posturing is very effective, and adjacent males rarely contest established boundaries. However, fights between resident and intruding males may be vigorous; puncture wounds inflicted by the horns may be fatal. In the high-density population around Lake Nakuru, territory holders may have an alliance with 1-3 other adult males (called “satellite males”) who are tolerated within the territory throughout the year. These other males are submissive to the territory holder and help drive away competitors; in return, satellite males receive access to prime feeding areas and a much greater chance of gaining a territory themselves (twelve times greater than bachelor males). Young, non-territorial males (between nine months and six years of age) generally associate in bachelor herds. Old males ousted from a territory often remain solitary. Unlike female groups, bachelor herds are stable, with a hierarchy based on size. Male herds average 5-3 individuals, with pairs being particularly common. Typically ranging over 1 km? the home range of bachelor males is dependent on season and the occupancy of male territories.
Status and Conservation. Classified as Near Threatened on The IUCN Red List (as K. ellipsiprymnus defassa ). The Defassa Waterbuck has a wider geographical range than the closely related Ellipsen Waterbuck, but is less common and much more patchily distributed. The total population is estimated to be 95,000 individuals. Illegal hunting and displacement due to agriculture and settlement have resulted in significant declines in population numbers; the species has been eliminated from much of its former range in West Africa.
Bibliography. Dittrich (1972), East (1999), Estes (1991a, 1991b), Galat et al. (1992), Hanks et al. (1969), IUCN/ SSC Antelope Specialist Group (2008x), Kassa et al. (2008), Kingdon (1982), Lorenzen et al. (2006), Lydekker (1914), Malbrant & Maclatchy (1949), Smithers (1966), Spinage (1968, 1969a, 1969b, 1970), Tomlinson (1980b), Weigl (2005), Wirtz (1981, 1983), Wirtz & Kaiser (1988), Wirtz & Oldekop (1991).
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