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The waterbuck

21 November 2013

 

www.leopard.tvThe waterbuck Kobus ellipsiprymnus is one of five species of the genus Kobus. There are 12 subspecies of waterbuck in Africa and the southern African subspecies is Kobus ellipsiprymnus ellipsiprymnus. The waterbuck was first described scientifically as Antilope ellipsiprymna by W Ogilby in 1833 based on a mounted specimen in the collection of A Steedman that came from the upper Notwani River near Gaborone in Botswana. As Antilope only occurs in India, the genus was renamed Kobus by A Smith in 1840.

In adults, the bulls have a shoulder height of 1.2 m and a weight of 250 to 270 kg, and 1.1 m and 180 kg in cows. The woolly coat’s colour varies from dark to greyish brown and the bulls are darker than the cows. Only the southern waterbuck has a white crescent around the rump. The tail is long and has a black tuft, while the ears are short and rounded. The adult cows have a rudimentary horn as a bony hump on the top of the skull, but they rarely carry full horns. The horns of adult bulls are ringed for the first 75% of their length from the skull and appear at seven months of age. The calves are reddish-brown. The coat of an adult waterbuck is heavily impregnated by a smelly, musky and greasy secretion from two glands on the neck and two around the anus. This secretion has a water-proofing function and allows for the recognition of individuals in the population.

The southern waterbuck occurs from the northern and north-eastern regions of South Africa north to Uganda and Kenya. It mainly inhabits open savannas and wetlands, but it also occurs marginally in grasslands and closed savannas. It is water-dependent and drinks water by day, preferring natural waterholes. It drinks several times per day and the mean intake in 24 hours is around 9 litres. Its habitat has become fragmented due to poor grazing management. It is a strong swimmer that will cross rivers and streams to find food on islands.

The southern waterbuck depends on good quality forage. In the Kruger National Park, waterbuck require a habitat with a plant mass of around 800 kg per ha and consequently avoids overgrazed areas. It requires grasses that are at least 120 mm tall and is a mixed feeder which eats 84% grass, 15% browse and 1% wild fruits, while in wetlands it also eats reeds and rushes. It browses on the horn-pod tree Diplorynchus condylocarpon that occurs on Shayamanzi and eats the fruits of the marula tree Sclerocarya birrea. It mainly feeds at night, but also in the early morning and late evening. Because their main tall-grass food plants normally occur near water, the name waterbuck has erroneously been used to describe them.

The waterbuck is relatively inactive and seldom moves more than a kilometre in 24 hours, although young waterbuck may wander in the rainy season. The waterbuck can form aggregations of up to 45 animals by day which break up into smaller units at night. The adult bulls occupy territories throughout the year after reaching an age of at least five years, but young bulls leave the breeding herds to join bachelor herds when they are a year old. Territorial displays mainly involve aggressive body postures. The range of a breeding herd varies from 150 to 780 ha and it includes the territories of several bulls. Groups of subadults rest in a characteristic star-shaped formation.

Mating occurs throughout the year, but births peak in October, February and March. Sexual maturity is reached in the bulls when they are 14 months old, and 13 months in the cows. However, the bulls usually only mate for the first time when they are 60 to 72 months old, and the cows when 24 to 36 months old to give birth to their first calf when they are 32 to 44 months old. Gestation lasts from 270 to 280 days, and the reproduction rate of the adult cows is close to 100%. Twins and triplets are not uncommon and newly born calves hide themselves in brush and tall grass clumps for the first three weeks of age, suckling three to four times in 24 hours. The cow has four mammae and weans her young 180 to 210 days after their birth. In areas with large predators, especially lions and spotted hyaenas, up to 50% of the calves may die before becoming a year old. Individual growth is slow and a waterbuck only reaches its full weight as an adult when it is 42 months old. The interval between successive calving is 12 months and the mean life expectancy of a waterbuck is 17 years. The mean size of a breeding herd in the Kruger National Park is 9.9 animals, and 4.4 for a bachelor herd. The territorial bulls stay single. The population growth in the Kruger National Park is 13.4%, but with fewer predators it can reach 28%.

 

References:

Grubb, P 2005. Order Artiodactyla. In D E Wilson and D M Reeder (eds), Mammal species of the world, third edition. Baltimore: Johns Hopkins University Press, pp 697 – 698

Skinner, J D and C T Chimimba (eds) 2005. The mammals of the southern African subregion, third edition. Cambridge: Cambridge University Press, pp. 629 – 632.

article by Prof J du P Bothma

 

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