Waterbuck
The waterbuck is a large antelope found widely in sub-Saharan Africa. It is in the genus Kobus of the family Bovidae. It was first described by Irish naturalist William Ogilby in 1833. Its 13 subspecies are grouped under two varieties: the common or ellipsiprymnus waterbuck and the defassa waterbuck. Their coat colour varies from brown to grey. The long, spiral horns, present only on males, curve backward, then forward, and are long.
Waterbucks are rather sedentary in nature. As gregarious animals, they may form herds consisting of six to thirty 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 six to nine. The waterbuck cannot 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 7–8 months, followed by the birth of a single calf.
Waterbucks inhabit scrub and savanna areas along rivers, lakes, and valleys. Due to their requirement for grasslands and water, waterbucks 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 is downwards, especially that of the defassa, with large populations being eliminated from certain habitats because of poaching and human disturbance.
Taxonomy and etymology
The scientific name of the waterbuck is Kobus ellipsiprymnus. The waterbuck is one of the six species of the genus Kobus in the family Bovidae. It was first described by Irish naturalist William Ogilby in 1833. The generic name Kobus is a Neo-Latin word, originating from an African name, koba. The specific name ellipsiprymnus refers to the white, elliptical ring on the rump, from the Greek ' and '. The animal acquired the vernacular name "waterbuck" due to its heavy dependence on water as compared to other antelopes and its ability to enter into water for defence.The type specimen of the waterbuck was collected by South African hunter-explorer Andrew Steedman in 1832. This specimen was named Antilope ellipsiprymnus by Ogilby in 1833. This species was transferred to the genus Kobus in 1840, becoming K. ellipsiprymnus. It is usually known as the common waterbuck. In 1835, German naturalist Eduard Rüppell collected another specimen, which differed from Steedman's specimen in having a prominent white ring on its rump. Considering it a separate species, Rüppell gave it the Amharic name "defassa" waterbuck and scientific name Antilope defassa. Modern taxonomists, however, consider the common waterbuck and the defassa waterbuck a single species, K. ellipsiprymnus, given the large number of instances of hybridisation between the two. Interbreeding between the two takes place in the Nairobi National Park owing to extensive overlapping of habitats. Though both groups occur in Zambia as well, their ranges are separated by relief features or by the Muchinga escarpment.
Evolution
Not many fossils of the waterbuck have been found. Fossils were scarce in the Cradle of Humankind, occurring only in a few pockets of the Swartkrans. On the basis of Valerius Geist's theories about the relation of social evolution and dispersal in ungulates during the Pleistocene, the ancestral home of the waterbuck is considered to be the eastern coast of Africa, with the Horn of Africa to the north and the East African Rift Valley to the west.Subspecies
On the basis of coat colour, 37 subspecies of the waterbucks had been initially recognised. They were classified into two groups: the ellipsiprymnus waterbuck group and the defassa waterbuck group. Owing to the large number of variations in the coat colour in the defassa waterbuck group, as many as 29 subspecies were included in it; the ellipsiprymnus waterbuck group consisted of eight subspecies. In 1971, however, the number of subspecies was reduced to 13. The subspecies are listed below, along with notes about the former subspecies which were recombined into a single subspecies:- K. e. ellipsiprymnus group: Found in the Webi Shebeli river valley in southeastern Ethiopia; the Juba and Webi Shebeli river valleys in Somalia; essentially east of the Rift Valley in Kenya and Tanzania; east of the Rift Valley in the middle Zambezi and Luangwa valleys in Zambia; Malawi; Mozambique; east of the Kwando River in the Caprivi Strip of Namibia; eastern and northern Botswana; Zimbabwe; and eastern and northern Transvaal in South Africa. Its distribution slightly overlaps that of the typical defassa along the Rift Valley in Kenya and Tanzania, and that of the Crawshay defassa in the Rift Valley in Zambia.
- K. e. defassa group: Found mostly west of the Gregory Rift, ranging from Ethiopia west to Senegal and south to Zambia.
Description
The waterbuck has 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". The odor of this is so unpleasant that it repels predators. 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. A cream-coloured patch is on the throat. Waterbuck are characterised by a long neck and short, strong, 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 stands 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 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 behaviour
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, 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. A few females may form spinster herds. Though females are seldom aggressive, minor tension may arise in herds.Males start showing territorial behaviour from the age of 5 years, but are most dominant from 6 to 9 years. Territorial males hold territories 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 are 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 lions, spotted hyenas, leopards, cheetahs, African 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.