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Waterbuck

A Male Waterbuck in Tanzania

The waterbuck (Kobus ellipsiprymnus) is a large antelope found widely in sub-Saharan Africa. It is placed in the genus Kobus of the family Bovidae. It was first described by Irish naturalist William Ogilby in 1833. The thirteen subspecies are grouped under two varieties: the common or ellipsen waterbuck and the defassa waterbuck. The head-and-body length is typically between 177–235 cm (70–93 in) and the average height is between 120 and 136 cm (47 and 54 in). A sexually dimorphic antelope, males are taller as well as heavier than females. Males reach approximately 127 cm (50 in) at the shoulder, while females reach 119 cm (47 in). Males typically weigh 198–262 kg (437–578 lb) and females 161–214 kg (355–472 lb). The coat colour varies from brown to grey. The long, spiral horns, present only on males, curve backward, then forward and are 55–99 cm (22–39 in) long.

Waterbuck are rather sedentary in nature. A gregarious animal, the waterbuck may form herds consisting of six to 30 individuals. These groups are either nursery herds with females and their offspring or bachelor herds. Males start showing territorial behaviour from the age of five years, but are most dominant from the age of six to nine. The waterbuck can not tolerate dehydration in hot weather, and thus inhabits areas close to sources of water. Predominantly a grazer, the waterbuck is mostly found on grassland. In equatorial regions, breeding takes place throughout the year, but births are at their peak in the rainy season. The gestational period lasts for seven to eight months, followed by the birth of a single calf.

Waterbuck inhabit scrub and savanna areas along rivers, lakes and valleys. Due to their requirement for grasslands as well as water, the waterbuck have a sparse ecotone distribution. The IUCN lists the waterbuck as being of Least Concern. More specifically, the common waterbuck is listed as of Least Concern while the defassa waterbuck is Near Threatened. The population trend for both the common and defassa waterbuck is downwards, especially that of the latter, with large populations being eliminated from certain habitats because of hunting and human disturbance.

Description Edit

The waterbuck is the largest amongst the six species of Kobus. It is a sexually dimorphic antelope, with the males nearly 7 percent taller than females and around 8 percent longer. The head-and-body length is typically between 177–235 cm (70–93 in) and the average height is between 120 and 136 cm (47 and 54 in). Males reach approximately 127 cm (50 in) at the shoulder, while females reach 119 cm (47 in). The waterbuck is one of the heaviest antelopes. a newborn typically weighs 13.6 kg (30 lb), and growth in weight is faster in males than in females.[2] Males typically weigh 198–262 kg (437–578 lb) and females 161–214 kg (355–472 lb). The tail is 22–45 cm (8.7–17.7 in) long.

The waterbuck is of a robust build. The shaggy coat is reddish brown to grey, and becomes progressively darker with age. Males are darker than females. Though apparently thick, the hair is sparse on the coat. The hair on the neck is, however, long and shaggy. When sexually excited, the skin of the waterbuck secretes a greasy substance with the odour of musk, giving it the name "greasy kob". This secretion also assists in water-proofing the body when the animal dives into water. The facial features include a white muzzle and light eyebrows and lighter insides of the ears. There is a cream-coloured patch (called "bib") on the throat. Waterbuck are characterised by a long neck and short, strong and black legs. Females have two nipples. Preorbital glands, foot glands and inguinal glands are absent.

The common waterbuck and the defassa waterbuck are remarkably different in their physical appearances. Measurements indicate greater tail length in the latter, whereas the common waterbuck stand taller than the defassa waterbuck. However, the principal differentiation between the two types is the white ring of hair surrounding the tail on the rump, which is a hollow circle in the common waterbuck but covered with white hair in the defassa waterbuck. The long, spiral horns curve backward, then forward. Found only on males, the horns range from 55 to 99 cm (22 to 39 in) in length. To some extent, the length of the horns is related to the bull's age. A rudimentary horn in the form of a bone lump may be found on the skulls of females.

Ecology and Behavior Edit

Waterbuck are rather sedentary in nature, though some migration may occur with the onset of monsoon. A gregarious animal, the waterbuck may form herds consisting of six to 30 individuals. The various groups are the nursery herds, bachelor herds and territorial males. Herd size increases in summer, whereas groups fragment in the winter months, probably under the influence of food availability. As soon as young males start developing horns (at around seven to nine months of age), they are chased out of the herd by territorial bulls. These males then form bachelor herds and may roam in female home ranges. Females have home ranges stretching over 200–600 hectares (0.77–2.32 sq mi; 490–1,480 acres). A few females may form spinster herds. Though females are seldom aggressive, minor tension may arise in herds.

Males start showing territorial behavior from the age of five years, but are most dominant from the age of six to nine. Territorial males hold territories 4–146 hectares (0.015–0.564 sq mi; 9.9–360.8 acres) in size. Males are inclined to remain settled in their territories, though over time they may leave inferior territories for more spacious ones. Marking of territories includes no elaborate rituals - dung and urine are occasionally dropped. After the age of ten years, males lose their territorial nature and replaced by a younger bull, following which they recede to a small and unprotected area. There is another social group, that of the satellite males, which are mature bulls as yet without their own territories, who exploit resources, particularly mating opportunities, even in the presence of the dominant bull. The territorial male may allow a few satellite males into his territory, and they may contribute to its defence. However, gradually they may deprive the actual owner of his territory and seize the area for themselves. In a study in the Lake Nakuru National Park, only 7 percent of the adult males held territories, and only half of the territorial males tolerated one or more satellite males.

Territorial males may use several kinds of display. In one type of display, the white patch on the throat and between the eyes is clearly revealed, and other displays can demonstrate the thickness of the neck. These activities frighten trespassers. Lowering of the head and the body depict submission before the territorial male, who stands erect. Fights, which may last up to thirty minutes, involve threat displays typical of bovids accompanied by snorting. Fights may even become so violent that one of the opponents meets its death due to severe abdominal or thoracic wounds. A silent animal, the waterbuck makes use of flehmen response for visual communication and alarm snorts for vocal communication. Waterbuck often enter water to escape from predators which include lionsleopardscheetahsAfrican wild dogs and Nile crocodiles. However, it has been observed that the waterbuck does not particularly like being in water. Waterbuck may run into cover when alarmed, and males often attack predators.

Diet Edit

The waterbuck exhibits great dependence on water. It can not tolerate dehydration in hot weather, and thus inhabits areas close to sources of water. However, it has been observed that unlike the other members of its genus (such as the kob and puku), the waterbuck ranges farther into the woodlands while maintaining its proximity to water. With grasses constituting a substantial 70 to 95 percent of the diet, the waterbuck is predominantly a grazer frequenting grasslands. Reeds and rushes like Typha and Phragmites may also be preferred. A study found regular consumption of three grass species round the year: Panicum anabaptistumEchinochloa stagnina and Andropogon gayanusHyparrhenia involucrataAcroceras amplectens and Oryza barthiialong with annual species were the main preference in the early rainy season, while long life grasses and forage from trees constituted three-fourths of the diet in the dry season.

Though the defassa waterbuck were found to have a much greater requirement for protein than the African buffalo and the oryx, the waterbuck was found to spend much lesser time on browsing (eating leaves, small shoots and fruits) in comparison to the other grazers. In the dry season about 32 percent of the 24-hour day was spent in browsing, whereas no time was spent on it during the wet season. The choice of grasses varies with location rather than availability; for instance, in western Uganda, while Sporobolus pyramidalis was favoured in some places, Themeda triandra was the main choice elsewhere. The common waterbuck and the defassa waterbuck in the same area may differ in their choices; it has been observed that while the former preferred Heteropogon contortus and Cynodon dactylon, the latter showed less preference for these grasses.

Reproduction Edit

Waterbuck are slower than other antelopes in terms of the rate of maturity. While males become sexually mature at the age of six years, females reach maturity within two to three years. Females may conceive by the age of two-and-a-half years, and remain reproductive for another ten years. In equatorial regions, breeding takes place throughout the year, and births are at their peak in the rainy season. However, breeding is seasonal in the Sudan(south of Sahara), with the mating season lasting four months. The season extends for even longer periods in some areas of southern Africa. Oestrus lasts for a day or less.

Mating begins after the male confirms that the female is in oestrus, which he does by sniffing her vulva and urine. A resistive female would try to bite or even fight off an advancing male. The male exhibits flehmen, and often licks the neck of the female and rubs his face and the base of his horns against her back. There are several attempts at mounting before the actual copulation. The female shifts her tail to one side, while the male clasps her sides with his forelegs and rests on her back during copulation, which may occur as many as ten times.

The gestational period lasts for seven to eight months, followed by the birth of a single calf. Twins are rare. Pregnant females isolate themselves and into thickets as parturition approaches. Newborn calves can stand on their feet within half-an-hour of birth. The mother eats the afterbirth. She communicates with the calf by bleating or snorting. Calves are kept hidden for two to three weeks or even two months. At about three to four weeks, the calf begins following its mother, who signals it to do so by raising her tail. Though bereft of horns, mothers will fiercely defend their offspring from predators. Calves are weaned at eight months, following which time they join groups of calves of their own age. Young females remain with their mothers in nursery herds, or may also join bachelor herds. The waterbuck lives to 18 years in the wild and 30 years in captivity.

Distribution and Habitat Edit

The waterbuck is native to southern and eastern Africa (including countries such as Angola, Botswana, The Democratic Republic of Congo, Ethiopia, Kenya, Namibia, South Africa, Tanzania and Uganda) besides a few countries of western and northern Africa such as Chad, Côte d'Ivoire, Ghana, Mali, Niger, Nigeria and Senegal. Though formerly widespread in sub-Saharan Africa, its numbers have now decreased in most areas.

The common waterbuck is found east of the Eastern African Rift. Its southern range extends to the Hluhluwe-Umfolozi Game Reserve (KwaZulu Natal) and to central Namibia. By contrast, the defassa waterbuck inhabits western and central Africa. The defassa waterbuck occurs west of the Albertine Rift and ranges from Eritrea to Guinea Bissau in the southern Sahel, its most northerly point of distribution being in southern Mali. Its range also stretches east of the Congo basin through Zambia into Angola, while another branch extends to the Zaire River west of the Congo basin. While the common waterbuck is now extinct in Ethiopia, the defassa waterbuck has become extinct in Gambia.

Waterbuck inhabit scrub and savanna areas alongside rivers, lakes and valleys. Due to their requirement for grasslands as well as water, the waterbuck have a sparse distribution across ecotones (areas of interface between two different ecosystems). A study in the Ruwenzori Range showed that the mean density of waterbuck was 5.5 per square mile, and estimates in the Maasai Mara were as low as 1.3 per square mile. It has been observed that territorial size depends on the quality of the habitat, the age and health of the animal and the population density. The greater the age of the animal or the denser the populations, the smaller are the territories. In Queen Elizabeth National Park, females had home ranges 21–61 hectares (0.081–0.236 sq mi; 52–151 acres) in area whereas home ranges for bachelor males averaged between 24–38 hectares (0.093–0.147 sq mi; 59–94 acres). The oldest female (around 18 years old) had the smallest home range.

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