Waterbuck

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Waterbuck
Waterbuck, Katavi.jpg
A waterbuck in the Katavi National Park
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Subfamily: Reduncinae
Genus: Kobus
Species: K. ellipsiprymnus
Binomial name
Kobus ellipsiprymnus
(Ogilby, 1833)
Subspecies

See text

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. The various groups are the nursery herds, bachelor herds and territorial males. 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 frequents grasslands. In equatorial regions, breeding is generally perennial, and 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, while avoiding bushy and low-lying areas. Due to the requirement for grasslands as well as water, the waterbuck have a sparse ecotone distribution. The IUCN lists the waterbuck as 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 decreasing, especially that of the latter, with large populations being eliminated from their habitats due to hunting and human settlement.

Taxonomy and etymology[edit]

Rüppell's depiction of the defassa waterbuck (1835)

The scientific name of the waterbuck is Kobus ellipsiprymnus. The waterbuck is one of the six species of the genus Kobus and belongs to the family Bovidae. It was first described by Irish naturalist William Ogilby in 1833. The generic name Kobus is a New Latin word, originating from an African name, koba. The specific name ellipsiprymnus refers to the white elliptical ring on the rump,[2] from the Greek ellipes (ellipse) and prymnos (prumnos, hind part).[3] The animal acquired the vernacular name "waterbuck" since it is largely dependent on water and can enter into it for defence.[4]

The type specimen of the waterbuck was collected by South African hunter-explorer Andrew Steedman in 1832. This specimen was named Antilope ellispiprymnus by Ogilby in 1833. This species was transferred to the genus Kobus and named K. ellipsiprymnus in 1840, 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.[2] Modern taxonomists, however, consider the common waterbuck and defassa waterbuck a single species, K. ellipsiprymnus, given the large number of instances of hybridisation between the two.[2] Interbreeding has been suggested in the Nairobi National Park owing to extensive overlapping of habitats.[5]

Evolution[edit]

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.[6] On the basis of Valerius Geist's theories about the relation of social evolution and dispersal in ungulates during the Pleistocene,[7] 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.[2]

Subspecies[edit]

K. e. ellipsiprymnus
K. e. defassa

37 subspecies of the waterbuck had been initially recognised on the basis of coat colour. They were classified into two groups: the Ellipsen 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 Ellipsen waterbuck group consisted of eight subspecies. In 1971, however, the number of subspecies was reduced to thirteen (four for the Ellipsen waterbuck group and nine for the Defassa waterbuck group). Though they occur in Zambia as well, their ranges are separated by relief features or by the Muchinga escarpment.[8] The subspecies have been listed below (along with notes about the former subspecies which were recombined into a single subspecies):[2][9]

  • K. e. ellipsiprymnus (Ellipsen waterbuck or common waterbuck) group: Found in southeastern Africa, ranging from southern Somalia to KwaZulu-Natal (South Africa) and inland to the Gregory Rift and Botswana. Includes the following four subspecies:
    • K. e. ellipsiprymnus Ogilby, 1833
    • K. e. kondensis Matschie, 1911 (including K. e. lipuwa, K. e. kulu)
    • K. e. pallidus Matschie, 1911
    • K. e. thikae Matschie, 1910 (including K. e. kuru and K. e. canescens)
  • K. e. defassa (Defassa waterbuck) group: Found west of the Gregory Rift, ranging from Ethiopia west to Senegal and south to Zambia. Includes the following nine subspecies:
    • K. e. adolfi-friderici Matschie, 1906 (including K. e. fulvifrons, K. e. nzoiae and K. e. raineyi)
    • K. e. annectens Schwarz, 1913 (including K. e. schubotzi)
    • K. e. crawshayi P. L. Sclater, 1894 (including K. e. uwendensis, K. e. frommiand K. e. münzneri)
    • K. e. defassa Rüppell, 1835 (including K. e. matschiei and K. e. hawashensis)
    • K. e. harnieri Murie, 1867 (including K. e. avellanifrons, K. e. ugandae, K. e. dianae, K. e. ladoensis, K. e. cottoni, K. e. breviceps, K. e. albertensis and K. e. griseotinctus)
    • K. e. penricei W. Rothschild, 1895
    • K. e. tjäderi Lönnberg, 1907 (including K. e. angusticeps and K. e. powelli)
    • K. e. tschadensis Schwarz, 1913
    • K. e. unctuosus Laurillard, 1842 (including K. e. togoensis)
The white ellipse on the rump of the common waterbuck
The white rump patch on the rump of the defassa waterbuck

Description[edit]

The waterbuck is the largest of the kob antelopes.[2] It is a sexually dimorphic antelope, with the males larger and heavier than the females.[8] 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).[10] Males are nearly 7 percent taller than females and around 8 percent longer in the head-and-body length.[2] 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).[11] The tail is 22–45 cm (8.7–17.7 in) long.[3]

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.[12] 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".[2][11] This secretion also assists in water-proofing the body when the animal dives into water.[12] 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.[3][10] Females have two nipples.[8]

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.[13] 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.[11]

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.[11] 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, while, in rare occurrences, a loose turn of a horn may be visible.[12]

Diseases and parasites[edit]

Waterbuck are susceptible to ulcers, lungworm infection and kidney stones. Other diseases these animals suffer from are foot-and-mouth disease, sindbis fever, yellow fever, bluetongue, bovine virus diarrhoea, brucellosis and anthrax. The waterbuck is more resistant to rinderpest than are other antelopes. Though unaffected by tsetse flies, ticks introduce into them protozoa such as Theileria parva, Anaplasma marginale and Baberia bigemina. 27 ixodid tick species have been found on waterbuck - a healthy waterbuck carries over 4000 ticks in their larva or nymph stage, the most common among them being Amblyomma cohaerens and Rhipicephalus tricuspis. Internal parasites found in waterbuck are tapeworms, liverflukes, stomachflukes and several helminths.[14][13]

Ecology and behaviour[edit]

A female herd in the Samburu National Park (Kenya)

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 summers, whereas groups fragment in the winter months, probably under the influence of food availability.[15] As soon as young males start developing horns (at around seven to nine months of age), they are chased out by territorial bulls. These males then form bachelor herds and may roam in female territories.[3] Young females remain with their mothers in nursery herds, and may also join bachelor herds.[8] Females own home ranges stretching over 200–600 hectares (0.77–2.32 sq mi; 490–1,480 acres). A few females may form spinster herds.[16] Though females are hardly aggressive, minor tension may arise in herds.[13]

Males start showing territorial behaviour from the age of five years, but are most dominant from the age of six to nine. Territorial males hold home ranges 4–146 hectares (0.015–0.564 sq mi; 9.9–360.8 acres) large. Males are inclined to remain settled in their territories, though over time they leave older territories for more spacious ones. Marking of territories includes no elaborate rituals - dung and urine are occasionally dropped.[16] After the age of ten years, males lose their territorial nature and lose to a younger bull, following which they recede to a small and unprotected area.[13] There is another social group, that of the satellite males, which are partly dominant bulls 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, who contribute to the defence of the territory. However, gradually they might 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.[17][18]

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 feature 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.[8] Fights, which may last till thirty minutes, involve threat displays typical of bovids accompanied by snorting.[16] Fights might even become so violent that one of the opponents meets its death due to severe abdominal and thoracic wounds.[11] 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 predators, that include lions, leopards, cheetahs, African wild dogs and Nile crocodiles (leopards and spotted hyenas prey on juveniles).[13] However, it has been observed that the waterbuck does not particularly like being in water.[19] Waterbuck may run into cover when alarmed, and males could fight predators by themselves.[11]

Diet[edit]

The waterbuck is predominantly a grazer.

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.[19] Predominantly a grazer, the waterbuck frequents grasslands. Grasses constitute a substantial 70 to 95 percent of the diet. Reeds and rushes like Typha and Phragmites may also be preferred.[13] A study found regular consumption of three grass species round the year: Panicum anabaptistum, Echinochloa stagnina and Andropogon gayanus. Hyparrhenia involucrata, Acroceras amplectens and Oryza barthii along 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.[20]

Though the defassa waterbuck were found to have a much greater requirement for protein than the African buffalo and the Beisa oryx, the waterbuck was found to spend much lesser time on browsing 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.[13]

Reproduction[edit]

A female waterbuck with her young

Waterbuck are slower than other antelopes in terms of the rate of maturity.[11] While males become sexually mature at the age of six years, females reach maturity within two to three years.[10] Females may conceive by the age of two-and-a-half years, and remain reproductive for another ten years.[13] In equatorial regions, breeding is generally perennial, 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.[11]

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 a 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.[11][8]

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 go into thickets. Newborn can stand on their feet as soon as half-an-hour after the birth.[10] The mother eats the afterbirth. She communicates with the calf by bleating or snorting.[8] 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 would fiercely defend their offspring from predators. Calves are weaned at eight months, following which they join groups of calves of their age.[11] The waterbuck live to 18 years in the wild and 30 years in captivity.[13]

Distribution and habitat[edit]

Waterbuck inhabit grasslands close to water.

The waterbuck is native to Angola, Benin, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Chad, The Democratic Republic of the Congo, Côte d'Ivoire, Eritrea, Ethiopia, Gabon, Ghana, Guinea-Bissau, Kenya, Malawi, Mali, Mozambique, Namibia, Niger, Nigeria, Rwanda, Senegal, Sierra Leone, Somalia, South Africa, South Sudan, Sudan, Swaziland, Tanzania, Togo, Uganda, Zambia and Zimbabwe. Though formerly widespread in sub-Saharan Africa, its numbers have now decreased in most areas.[1]

The common waterbuck is found east to the Eastern African Rift. Its southern range extends till Hluhluwe-Umfolozi Game Reserve (KwaZulu Natal) and to central Namibia. To the contrary, 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 are extinct in Ethiopia, the defassa waterbuck is no more present in Gambia.[1]

Waterbuck inhabit scrub and savanna areas along rivers, lakes and valleys,[12] while avoiding bushy and low-lying areas.[11] Due to the requirement for grasslands as well as water, the waterbuck have a sparse ecotone distribution. 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 favourability of habitat, age and health of the animal and population density. The more the age of the animal or the denser the populations, the smaller are the territories. In Queen Elizabeth National Park, females held territories ranging 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 territory.[11]

Threats and conservation[edit]

Horns of a waterbuck displayed at a shop. Hunting for commercial purposes is a major threat to the waterbuck.

The International Union for the Conservation of Nature and Natural Resources (IUCN) lists the waterbuck as 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 decreasing, especially that of the latter, with large populations being eliminated from their habitats due to hunting and human settlement. Their own sedentary nature too is responsible for this to some extent. Numbers have fallen in Queen Elizabeth National Park, Murchison Falls National Park, Akagera National Park, Lake Nakuru National Park, and Comoé National Park.[1] Population decrease in the Lake Nakuru National Park has been attributed to heavy metal poisoning in the animals. While cadmium and lead levels were dangerously high in the kidney and the liver, copper, calcium and phosphorus deficiency was noted.[21]

Over 60 percent of the defassa waterbuck populations thrive in protected areas, most notably in Niokolo-Koba, Comoe, Mole, Bui, Pendjari, Manovo-Gounda St. Floris, Moukalaba-Doudou, Garamba, Virunga, Omo, Mago, Murchison Falls, Serengeti, and Katavi, Kafue and Queen Elizabeth National Parks, the national parks and hunting zones of North Province (Cameroon), Ugalla River Forest Reserve, Nazinga Game Ranch, Rukwa Valley, Awash Valley, Murule and Arly-Singou. The common waterbuck occurs in Tsavo, Tarangire, Mikumi, Kruger and Lake Nakuru National Parks, Laikipia, Kajiado, Luangwa Valley, Selous and Hluhluwe-Umfolozi game reserves and private lands in South Africa.[1][13]

References[edit]

  1. ^ a b c d e IUCN SSC Antelope Specialist Group (2008). "Kobus ellipsiprymnus". IUCN Red List of Threatened Species. Version 2010.4. International Union for Conservation of Nature. Retrieved 2011-06-15.  Database entry includes justification for why this species is listed as Least concern.
  2. ^ a b c d e f g h i Spinage, C.A. (1982). A Territorial Antelope : The Uganda Waterbuck. London: Academic Press. pp. 4–6, 10, 18–19, 56–63. ISBN 0-12-657720-X. 
  3. ^ a b c d Huffman, B. "Waterbuck". Ultimate Ungulate. Retrieved 21 March 2014. 
  4. ^ Taylor, C.R.; Spinage, C.A.; Lyman, C.P. (1969). "Water relations of the waterbuck, an East African antelope". The American Journal of Physiology 217 (2): 630–4. PMID 5799396. 
  5. ^ Lorenzen, E. D.; Simonsen, B. T.; Kat, P. W.; Arctander, P.; Siegismund, H. R. (14 August 2006). "Hybridization between subspecies of waterbuck (Kobus ellipsiprymnus) in zones of overlap with limited introgression". Molecular Ecology 15 (12): 3787–99. doi:10.1111/j.1365-294X.2006.03059.x. 
  6. ^ Hilton-Barber, B.; Mbeki, L. R. B. (2004). Field Guide to the Cradle of Humankind : Sterkfontein, Swartkrans, Kromdraai & Environs World Heritage Site (2nd revised ed.). Cape Town: Struik. p. 171. ISBN 1-77007-065-6. 
  7. ^ Geist, V. "The relation of social evolution and dispersal in ungulates during the Pleistocene, with emphasis on the old world deer and the genus Bison". Quaternary Research 1 (3): 285–315. doi:10.1016/0033-5894(71)90067-6. 
  8. ^ a b c d e f g Skinner, J. D.; Chimimba, Christian T. (2005). The Mammals of the Southern African Subregion (3rd ed.). Cambridge: Cambridge University Press. pp. 681–2. ISBN 0521844185. 
  9. ^ Wilson, D. E.; Reeder, D. M., eds. (2005). Mammal Species of the World (3rd ed.). Johns Hopkins University Press. p. 720. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  10. ^ a b c d Newell, T. L. "Kobus ellipsiprymnus (Waterbuck)". University of Michigan Museum of Zoology. Animal Diversity Web. Retrieved 21 March 2014. 
  11. ^ a b c d e f g h i j k l Estes, R. D. (2004). The Behavior Guide to African Mammals : Including Hoofed Mammals, Carnivores, Primates (4th ed.). Berkeley: University of California Press. pp. 107–11. ISBN 0-520-08085-8. 
  12. ^ a b c d Kingdon, J. (1989). East African Mammals : An Atlas of Evolution in Africa. Chicago: University of Chicago press. pp. 385–91. ISBN 0-226-43724-8. 
  13. ^ a b c d e f g h i j Kingdon, J.; Hoffman, M. Mammals of Africa (Volume VI): Hippopotamuses, Pigs, Deer, Giraffe and Bovids. Bloomsbury. pp. 461–8. 
  14. ^ Groocock, C.M.; Staak, C. (1969). "The isolation of Brucella abortus from a waterbuck (Kobus ellipsiprymnus)". The Veterinary Record 85 (11): 318. PMID 4980299. 
  15. ^ Melton, D. A. (1978). Ecology of waterbuck Kobus ellipsiprymnus (Ogilby, 1833) in the Umfolozi Game Reserve. Pretoria: University of Pretoria. 
  16. ^ a b c Spinage, C. A. (2010). "Territoriality and social organization of the Uganda defassa waterbuck Kobus defassa ugandae". Journal of Zoology 159 (3): 329–61. doi:10.1111/j.1469-7998.1969.tb08452.x. 
  17. ^ Wirtz, P. "Territorial defence and territory take-over by satellite males in the waterbuck Kobus ellipsiprymnus (Bovidae)". Behavioral Ecology and Sociobiology 8 (2): 161–2. doi:10.1007/BF00300830. 
  18. ^ Wirtz, P. (2010). "Territory holders, satellite males and bachelor males in a high density population of waterbuck (Kobus ellipsiprymnus) and their associations with conspecifics". Zeitschrift für Tierpsychologie 58 (4): 277–300. doi:10.1111/j.1439-0310.1982.tb00322.x. 
  19. ^ a b Nowak, R. M. (1999). Walker's Mammals of the World (Volume 1) (6th ed.). Baltimore: Johns Hopkins University Press. pp. 1166–70. ISBN 0-8018-5789-9. 
  20. ^ Kassa, B.; Libois, R.; Sinsin, B. "Diet and food preference of the waterbuck in the Pendjari National Park, Benin". African Journal of Ecology 46 (3): 303–10. doi:10.1111/j.1365-2028.2007.00827.x. 
  21. ^ Jumba, I. O.; Kisia, S. M.; Kock, R. (2006). "Animal health problems attributed to environmental contamination in Lake Nakuru National Park, Kenya: A case study on heavy metal poisoning in the waterbuck Kobus ellipsiprymnus defassa (Ruppel 1835)". Archives of Environmental Contamination and Toxicology 52 (2): 270–81. doi:10.1007/s00244-005-0241-2. 

External links[edit]