Wildebeest

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This article is about the animal. For other uses, see Wildebeest (disambiguation).
Wildebeest
Blue wildebeest, Ngorongoro Crater, Tanzania
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Subphylum: Vertebrata
Class: Mammalia
Order: Artiodactyla
Family: Bovidae
Subfamily: Alcelaphinae
Genus: Connochaetes
Lichtenstein, 1812
Species

Connochaetes gnou – black wildebeest
Connochaetes taurinus – blue wildebeest

The wildebeest, also called the gnu is an antelope in the genus Connochaetes. It belongs to the family Bovidae, which includes antelopes, cattle, goats, sheep and other even-toed horned ungulates. Connochaetes includes two species, both native to Africa: the black wildebeest, or white-tailed gnu (C. gnou); and the blue wildebeest, or brindled gnu (C. taurinus). Fossil records suggest these two species diverged about one million years ago, resulting in northern and southern species. The blue wildebeest changed very little from the ancestor species, while the black wildebeest took on more morphological changes to adapt to a habitat of open grassland in the south. Today, the blue wildebeest has five subspecies, while the black wildebeest has no named subspecies.[1] In East Africa, the wildebeest is the most abundant big-game species, both in population and biomass.[2]

Etymology

The wildebeest (/ˈwɪldəbiːst/ WIL-də-beest[3][4][5] or /ˈvɪl-/ VIL-,[5] plural wildebeest or wildebeests, wildebeesties (juv)), also called the gnu (/ˈnuː/ NOO[6][7][8] or /ˈnjuː/ NEW)[6][8] is an antelope of the genus Connochaetes. Wildebeest is Dutch for "wild beast" or "wild cattle" in Afrikaans (bees = cattle), while Connochaetes derives from the Greek words κόννος, kónnos, "beard", and χαίτη, khaítē, "flowing hair", "mane".[9] The name "gnu" originates from the Khoikhoi name for these animals, gnou.[10]

Taxonomy and evolution

The wildebeest, or the genus Connochaetes, is placed under family Bovidae and subfamily Alcelaphinae.[11] The name Connochaetes was given by German zoologist Martin Hinrich Carl Lichtenstein in 1814.[12][11] This genus consists of two species: the black wildebeest (C. gnou) and the blue wildebeest (C. taurinus). However, this has not always been the case. In the past, the blue wildebeest had been placed under a separate genus of its own, Gorgon.[12][13]

According to an mtDNA analysis, the black wildebeest seem to have diverged from the main lineage during the Middle Pleistocene and became a distinct species around a million years ago.[14] A divergence rate of approximately 2% has been calculated.[13] The split does not seem to have been driven by competition for resources but instead by the fact that each species adopted a different feeding niche and occupied a different trophic level.[15]

Blue wildebeest fossils dating back some two and a half million years ago are common and widespread. They have been found in the fossil bearing caves at the Cradle of Humankind north of Johannesburg. Elsewhere in South Africa they are plentiful at such sites as Elandsfontein, Cornelia and Florisbad.[16] The earliest fossils of the black wildebeest were found in sedimentary rock in Cornelia in the Orange Free State and dated back about eight hundred thousand years.[15]

Genetics and hybrids

The diploid number of chromosomes in the wildebeest is 58.[17] Chromosomes were studied in a male and a female wildebeest. In the female, all except a pair of very large submetacentric chromosomes were found to be acrocentric. Metaphases were studied in the male's chromosomes, and very large submetacentric chromosomes were found there as well, similar to those in the female both in size and morphology. Other chromosomes were acrocentric. The X chromosome is a large acrocentric and the Y chromosome a minute one.[18][11]

The two species of the wildebeest are known to hybridise. Male black wildebeest have been reported to mate with female blue wildebeest and vice versa.[19] The differences in social behaviour and habitats have historically prevented interspecific hybridisation between the species, however hybridisation may occur when they are both confined within the same area. The resulting offspring is usually fertile. A study of these hybrid animals at Spioenkop Dam Nature Reserve in South Africa revealed that many had disadvantageous abnormalities relating to their teeth, horns and the wormian bones in the skull.[20] Another study reported an increase in the size of the hybrid as compared to either of its parents. In some animals the auditory bullae are highly deformed and in others the radius and ulna are fused.[21]

Physiology

A full-grown wildebeest can be 1.27–1.47 m (4.2–4.8 ft) at the shoulder and weigh 120–270 kg (260–600 lb). They inhabit the plains and open woodlands of Africa, especially the Serengeti National Park, a UNESCO World Heritage Site in Tanzania, Masai Mara Game Reserve in Kenya, and Liuwa Plain National Park in Zambia. Wildebeest can live more than 40 years, though their average lifespan is around 20 years.[22] The wildebeest has a broad muzzle which helps it to eat short grass.[2]

Differences between blue and black wildebeest

  • Blue wildebeest at Mikumi National Park, Tanzania

  • Black wildebeest at Kliprivier Nature Reserve, Johannesburg

The most striking morphological differences between the black and blue wildebeest are the orientation and curvature of their horns and the color of their coats. The blue wildebeest is the bigger of the two species. In males, blue wildebeest stand 150 cm tall at the shoulder and weigh around 250 kg,[23] while the black wildebeest stands 111 to 120 cm tall[24] and weighs about 180 kg.[25] In females, blue wildebeest have a shoulder height of 135 cm and weigh 180 kg[23] while black wildebeest females stand 108 cm at the shoulder and weigh 155 kg.[25] The horns of blue wildebeest protrude to the side then curve downwards before curving up back towards the skull, while the horns of the black wildebeest curve forward then downward before curving upwards at the tips. Blue wildebeest tend to be a dark grey color with stripes, but may have a shiny blue color. The black wildebeest has brown-coloured fur, with a mane that ranges in color from cream to black, and a cream-coloured tail end. The blue wildebeest lives in a wide variety of habitats, including woodlands and grasslands, while the black wildebeest tends to reside exclusively in open grassland areas.[1] The blue wildebeest migrates over long distances in the winter, whereas the black wildebeest does not.[26] The milk of the female black wildebeest contains higher protein, lower fat, and lower lactose content than the milk of female blue wildebeest.[27]

Migration

Wildebeest herding and following zebra in the Serengeti National Park (Tanzania). During these migrations, wildebeest spend 10 months per year in the Serengeti National Park and two months in the Masai Mara, (Kenya).

Not all wildebeest are migratory. Black wildebeest herds are often nomadic or may have a regular home range of 1 km2 (11,000,000 sq ft). Bulls may occupy territories, usually about 100 to 400 m (328 to 1,312 ft) apart, but this spacing varies according to the quality of the habitat. In favourable conditions they may be as close as 9 m (30 ft) or as far apart as 1,600 m (5,200 ft) in poor habitat.[12] Female herds have home ranges of about 250 acres (100 ha; 0.39 sq mi) in size. Herds of non-territorial batchelor males roam at will and do not seem to have a home range.[28]

In the Masai Mara game reserve, there is a non-migratory population of blue wildebeest which had dwindled from about 119,000 animals in 1977 to about 22,000 in 1997. The reason for the decline is thought to be the increasing competition between cattle and wildebeest for a dwindling area of grazing land as a result of changes in agricultural practices, and possibly fluctuations in rainfall.[29]

Each year, some East African populations of blue wildebeest have a long-distance migration, seemingly timed to coincide with the annual pattern of rainfall and grass growth. The timing of their migrations in both the rainy and dry seasons can vary considerably (by months) from year to year. At the end of the rainy season (May or June in East Africa), wildebeest migrate to dry-season areas in response to a lack of surface (drinking) water. When the rainy season begins again (months later), animals quickly move back to their wet-season ranges. Factors suspected to affect migration include food abundance, surface water availability, predators, and phosphorus content in grasses. Phosphorus is a crucial element for all life forms, particularly for lactating female bovids. As a result during the rainy season, wildebeest select grazing areas that contain particularly high phosphorus levels.[2] One study found, in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content.[30] Large-scale wildebeest migration is quite likely a consequence of decisions being made by individuals at multiple spatial scales, involving a balance of food abundance, food quality, local density of other wildebeest, social interactions, surface water, perceived predation risk, and culturally (or possibly genetically) learned routes and ranges.

Wildebeest in Masai Mara during the Great Migration

Numerous documentaries feature wildebeest crossing rivers, with many being eaten by crocodiles or drowning in the attempt. While having the appearance of a frenzy, recent research has shown a herd of wildebeest possesses what is known as a "swarm intelligence", whereby the animals systematically explore and overcome the obstacle as one.[31] Major predators that feed on wildebeest include the lion, hyena, cheetah, leopard, and crocodile, which seem to favour the wildebeest.[22] Wildebeest, however, are very strong, and can inflict considerable injury even to a lion. Wildebeest have a maximum running speed of around 80 km/h (50 mph).[32][33] The primary defensive tactic is herding, where the young animals are protected by the older, larger ones, while the herd runs as a group. Typically, the predators attempt to cut out a young or ill animal and attack without having to worry about the herd. Wildebeest have developed additional sophisticated cooperative behaviours, such as animals taking turns sleeping while others stand guard against a night attack by invading predators. Scientists are unsure how much is learned behaviour and how much is instinct.[citation needed] Wildebeest migrations are closely followed by vultures, as wildebeest carcasses are an important source of food for these scavengers. The vultures consume about 70% of the wildebeest carcasses available. Decreases in the number of migrating wildebeest have also had a negative effect on the vultures.[34] In the Serengeti ecosystem, Tanzania, wildebeest may help facilitate the migration of other, smaller-bodied grazers, such as Thomson's gazelles (Eudorcas thomsonii), which eat the new-growth grasses stimulated by wildebeest foraging.

Interactions with nonpredators

Zebras and wildebeest group together in open savannah environments with high chances of predation. This grouping strategy reduces predation risk because larger groups decrease each individual’s chance of being hunted, and predators are more easily seen in open areas.[35]

Wildebeest can also listen in on the alarm calls of other species, and by doing so can reduce their risk of predation. One study showed, along with other ungulates, wildebeests responded more strongly to the baboon alarm calls compared to the baboon contest calls, though both types of calls had similar patterns, amplitudes, and durations. The alarm calls were a response of the baboons to lions, and the contest calls were recorded when a dispute between two males occurred.[36]

Breeding and reproduction

Video of wildebeest feeding its calf, South Africa

Because of their migratory ways, the wildebeest do not form permanent pair bonds. The wildebeest mating season, rut, is when the males establish temporary territories and try to attract females. These small territories are about 3000 m2, with up to 300 territories per km2. The males defend these small territories from other males while trying to attract females that are ready to mate. The males entice females into their territories with grunts and distinctive antics. Wildebeest usually breed at the end of the rainy season when the animals are most fit.[2] The mating season usually occurs between May and July, and birthing usually takes place between January and March, at the start of the wet season. The gestation period is about eight to nine months, and the average estrous cycle is about 23 days. Wildebeest females breed seasonally and ovulate spontaneously.[37] Groups of wildebeest females and young live in the small areas established by the male. When groups of wildebeest join together, the female to male ratio is larger, as the females flock to the areas held by fewer males.[35] This female-dominated sex ratio may be due to illegal hunting and human disturbance. Higher male mortality has been attributed to illegal hunting.[38]

Conservation and management

Wildebeest still number in the thousands, or even hundreds of thousands, in numerous areas in eastern and southern Africa, which is a testament to the local efforts and foresight to conserve and manage these animals. However, many wildebeest populations are experiencing rapid declines. Overland migration as a biological process requires large connected landscapes, which are increasingly difficult to maintain, particularly over the long term, when human demands on the landscape compete, as well. The most acute threat comes from migration barriers, such as fences and roads. In one of the more striking examples of the consequences of fence-building on terrestrial migrations, Botswanan authorities placed thousands of kilometres of fences across the Kalahari that prevented wildebeests from reaching watering holes and grazing grounds, resulting in the deaths of tens of thousands of individuals, and dropping the wildebeest population to less than 10% of its previous size.[39] Wildebeest migrations in the Serengeti and Tarangire ecosystems, Tanzania, are also threatened by the construction of a roadway across their northern portions. The impact of this road on migratory wildlife will undoubtedly be negative and reduce the aesthetic value of the ecosystems, but the magnitude of the impact (in numerical terms) on the population will depend on the extent to which the road acts as a barrier to movement, causes collision mortalities, and opens the area to illegal hunting. In addition to roads and fences, illegal hunting is a major conservation concern in many areas. In the western Serengeti, scientists estimate tens of thousands of animals are poached each year, largely using wire snares. Other ecosystems are experiencing similar pressures, such as the Tarangire ecosystem in Tanzania, which historically supported large numbers of migratory wildebeest (as well as other species), but has recently declined in number, coincident with illegal hunting and land-use changes across the rainy season ranges. An important question in populations threatened by barriers and other pressures is whether and how they adjust to a less migratory lifestyle. Although the majority of wildebeest populations migrate, some populations do not, and appear to never have done so in recorded history. Such populations can be found in the Ngorongoro Crater, the Masai Mara, Lake Manyara National Park, Selous Game Reserve, and Hwange and Etosha National Parks.[2]

Hunting

Wildebeest are killed for food, especially to make biltong in Southern Africa. This dried game meat is a delicacy and an important food item in Africa.[2] The meat of females is more tender than that of males, and is the most tender during the autumn season.[26] Wildebeest are a regular target for illegal meat hunters because their numbers make them easy to find. Cooks preparing the wildebeest carcass usually cut it into 11 pieces. The estimated price for wildebeest meat was about US$ 0.47 per kilogram around 2008.[40]

References

  1. ↑ 1.0 1.1 Ackermann, Rebecca; James S. Brink, Savvas Vrahimis, Bonita de Klerk (2010). "Hybrid Wildebeest (Artiodactyla: Bovidae) Provide Further Evidence For Shared Signatures of Admixture in Mammalian Crania". South African Journal of Science 106 (11/12): 90–94. doi:10.4102/sajs.v106i11/12.423. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Ulfstrand, Staffan (2002). Savannah Lives: Animal Life and Human Evolution in Africa. Oxford University Press. 
  3. ↑ Dictionary Reference: wildebeest
  4. ↑ Cambridge Dictionary: wildebeest
  5. ↑ 5.0 5.1 The Free Dictionary: wildebeest
  6. ↑ 6.0 6.1 Dictionary Reference: gnu
  7. ↑ Cambridge Dictionary: gnu
  8. ↑ 8.0 8.1 The Free Dictionary: gnu
  9. ↑ Comparative Placentation: Wildebeest, Gnu
  10. ↑ "Gnu". Merriam-Webster. Retrieved 14 January 2014. 
  11. ↑ 11.0 11.1 11.2 Groves, C.; Grubb, P. (2011). Ungulate Taxonomy. Baltimore, Maryland: Johns Hopkins University Press. ISBN 1-4214-0093-6. 
  12. ↑ 12.0 12.1 12.2 Nowak, R. M. (1999). Walker's Mammals of the World (6th ed.). Johns Hopkins University Press. pp. 1184–6. ISBN 0-8018-5789-9. 
  13. ↑ 13.0 13.1 Corbet, S. W.; Robinson, T. J. (1991 November-December). "Genetic divergence in South African Wildebeest: comparative cytogenetics and analysis of mitochondrial DNA". The Journal of Heredity 82 (6): 447–52. PMID 1795096. 
  14. ↑ Bassi, J. (2013). Pilot in the Wild: Flights of Conservation and Survival. Jacana Media. pp. 116–118. ISBN 978-1-4314-0871-9. 
  15. ↑ 15.0 15.1 Codron, Daryl; Brink, James S. (2007). "Trophic ecology of two savanna grazers, blue wildebeest Connochaetes taurinus and black wildebeest Connochaetes gnou". European Journal of Wildlife Research 53 (2): 90–99. doi:10.1007/s10344-006-0070-2. 
  16. ↑ B., Hilton-Barber; Berger, L. R. (2004). Field Guide to the Cradle of Humankind : Sterkfontein, Swartkrans, Kromdraai & Environs World Heritage Site (2nd ed.). Cape Town: Struik. pp. 162–3. ISBN 978-177-0070-653. 
  17. ↑ Skinner, J. D.; Chimimba, C. T. (2005). The Mammals of the Southern African Subregion (3rd ed.). Cambridge: Cambridge University Press. pp. 645–8. ISBN 978-0-521-84418-5. 
  18. ↑ Wallace, C. (1978). "Chromosome analysis in the Kruger National Park: The chromosomes of the blue wildebeest Connochaetes taurinus". Koedoe 21 (1): 195–6. doi:10.4102/koedoe.v21i1.974. 
  19. ↑ Grobler, J. P.; Rushworth, I.; Brink, J. S.; Bloomer, P.; Kotze, A.; Reilly, B.; Vrahimis, S. (5 August 2011). "Management of hybridization in an endemic species: decision making in the face of imperfect information in the case of the black wildebeest—Connochaetes gnou". European Journal of Wildlife Research 57 (5): 997–1006. doi:10.1007/s10344-011-0567-1. ISSN 1439-0574. 
  20. ↑ Ackermann, R. R.; Brink, J. S.; Vrahimis, S.; De Klerk, B. (29 October 2010). "Hybrid wildebeest (Artiodactyla: Bovidae) provide further evidence for shared signatures of admixture in mammalian crania". South African Journal of Science 106 (11/12): 1–4. doi:10.4102/sajs.v106i11/12.423. 
  21. ↑ De Klerk, B. (2008). An osteological documentation of hybrid wildebeest and its bearing on black wildebeest (Connochaetes gnou) evolution (Doctoral dissertation). 
  22. ↑ 22.0 22.1 "Wildebeest". National Geographic. Retrieved 16 December 2010. 
  23. ↑ 23.0 23.1 "Trophy Hunting Blue Wildebeest in South Africa". 
  24. ↑ Lundrigan, Barbara. [http://animaldiversity.ummz.umich.edu/site/accounts/information/Connochaetes_gnou.html. "Connochaetes gnou"]. Retrieved 29 April 2011. 
  25. ↑ 25.0 25.1 "Trophy Hunting Black Wildebeest in South Africa". 
  26. ↑ 26.0 26.1 Hoffman, Louw; Schalkwyk, Sunet van; Muller, Nina (2009). "Effect of Season and Gender on the Physical and Chemical Composition of Black Wildebeest (Connochaetus Gnou) Meat". South African Journal of Wildlife Research 39 (2): 170–174. doi:10.3957/056.039.0208. 
  27. ↑ Osthoff, G.; A. Hugo, M. de Wit (2009). "Comparison of the Milk Composition of Free-ranging Blesbok, Black Wildebeest and Blue Wildebeest of the Subfamily Alcelaphinae (family: Bovidae)". Comparative Biochemistry and Physiology Part B: Biochemistry and Molecular Biology 154 (1): 48–54. doi:10.1016/j.cbpb.2009.04.015. 
  28. ↑ Huffman, B. "Connochaetes gnou: White-tailed gnu, Black wildebeest". Ultimate Ungulate. Retrieved 2014-01-19. 
  29. ↑ Ottichiloa, Wilber K.; de Leeuwa, Jan; Prins, Herbert H. T. (2001). "Population trends of resident wildebeest [Connochaetes taurinus hecki (Neumann)] and factors influencing them in the Masai Mara ecosystem, Kenya". Biological Conservation 97 (3): 271–282. doi:10.1016/S0006-3207(00)00090-2. 
  30. ↑ Ben-Shahar, Raphael; Malcolm J. Coe (1992). "The Relationships between Soil Factors, Grass Nutrients, and the Foraging Behaviour of Wildebeest and Zebra". Oecologia 90 (3): 422–428. doi:10.1007/BF00317701. 
  31. ↑ "Wildebeest Migration – Must See on African Safari Vacation". Tanzenar. 4 June 2009. Retrieved 16 December 2010. 
  32. ↑ PBS. "Animal Guide: Blue Wildebeest". Nature. Retrieved 8 January 2013. 
  33. ↑ McGowan, Christopher (28 February 1999). A Practical Guide to Vertebrate Mechanics. Cambridge University Press. p. 162. ISBN 9780521576734. 
  34. ↑ Virani, Munir Z.; Corinne Kendall, Peter Njoroge, Simon Thomsett (2011). "Major Declines in the Abundance of Vultures and Other Scavenging Raptors in and around the Masai Mara Ecosystem, Kenya". Biological Conservation 144 (2): 746–752. doi:10.1016/j.biocon.2010.10.024. 
  35. ↑ 35.0 35.1 Thaker, Maria; Abi T. Vanak, Cailey R. Owen, Monika B. Ogden, Rob Slotow (2010). "Group Dynamics of Zebra and Wildebeest in a Woodland Savanna: Effects of Predation Risk and Habitat Density". In Getz, Wayne M. PLoS ONE 5 (9): e12758. doi:10.1371/journal.pone.0012758. PMC 2942830. PMID 20862216. 
  36. ↑ Kitchen, Dawn M.; Thore J. Berman, Dorothy L. Cheney, James R. Nicholson, Robert M. Seyfarth (2010). "Comparing Responses of Four Ungulate Species to Playbacks of Baboon Alarm Calls". Animal Cognition 13 (6): 861–870. doi:10.1007/s10071-010-0334-9. PMID 20607576. 
  37. ↑ Clay, A. Moss; R.D. Estes, K.V. Thompson, D.E. Wildt, S.L. Monfort (2010). "Endocrine Patterns of the Estrous Cycle and Pregnancy of Wildebeest in the Serengeti Ecosystem". General and Comparative Endocrinology 166 (2): 365–371. doi:10.1016/j.ygcen.2009.12.005. PMID 20036667. 
  38. ↑ Ndibalema, Vedasto G. (2009). "A Comparison of Sex Ratio, Birth Periods and Calf Survival among Serengeti Wildebeest Sub-populations, Tanzania". African Journal of Ecology 47 (4): 574–582. doi:10.1111/j.1365-2028.2008.00994.x. 
  39. ↑ Williamson, D.T.; B. Mbano (1988). "Wildebeest Mortality During 1983 at Lake Xau, Botswana". African Journal of Ecology 26: 341–344. 
  40. ↑ Ndibalema, Vedasto G.; Alexander N. Songorwa (2008). "Illegal Meat Hunting in Serengeti: Dynamics in Consumption and Preferences". African Journal of Ecology 46 (3): 311–319. doi:10.1111/j.1365-2028.2007.00836.x. 

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