A distinctive, high-shouldered antelope, with a long, broad muzzle and cow-like horns, the blue wildebeest is famous for forming vast migratory herds. The Male weighs up to 290 kg and Female weighs up to 260 kg. The species gets its common name from the silvery-blue sheen to the coat, the base colour of which varies from greyish to brown. The forequarters bear vertical black stripes - the ‘brindled’ colouration that gives the species one of its alternative names - and the front of the face, the long tail, and the mane are also black. The long beard may be black or white, depending on the subspecies. Both the male and female have unridged horns, which curve downward laterally before pointing upward and inward, and in older animals may have a knobby base.
Five subspecies of blue wildebeest are recognised: the western white-bearded wildebeest, the eastern white-bearded wildebeest, the Johnston’s or Nyassa wildebeest, Cookson’s wildebeest, and the blue wildebeest. the western white-bearded wildebeest, the smallest of these, with the shortest horns, is the subspecies which forms the famous large herds of the Serengeti - Masai Mara. The blue wildebeest can be distinguished from the black wildebeest (or white-tailed gnu).
Range: The blue wildebeest has a wide distribution from Kenya and Tanzania southwards, to Zambia, Namibia, Botswana, Mozambique, northern South Africa and southern Angola, and has been introduced to the Eastern Highlands of Zimbabwe and to farms in Namibia. Cookson’s wildebeest has probably the most restricted range, being found only in the Luangwa Valley in Zambia.
Habitat: Generally inhabiting open short-grass plains, as well as Acacia savannah, open bush land and woodland in drier areas, the blue wildebeest prefers habitats which are neither too dry nor too wet.
Status: Listed as Least Concern (LC) in IUCN Redlist.
Biology: The blue wildebeest is a grazer, its broad mouth adapted to bulk feeding on short grass. However, its dependence on short grass, together with its need to drink at least every other day, limits the species to moist grassland and to areas within reach of water, although interestingly it is also known to survive in waterless regions of the Kalahari by feeding on melons and water-storing roots and tubers. The need to follow seasonal grazing and water supplies leads the blue wildebeest to form some of the largest migratory herds of all antelopes, with those in the Serengeti-Masai Mara ecosystem of Kenya and Tanzania forming part of the world’s largest remaining aggregations of large land mammals. However, not all wildebeest migrate, with some remaining in the same area year-round, generally forming small herds of up to ten females plus immature offspring. The females in these herds tend to establish dominance hierarchies and harass any outsiders who attempt to join. In contrast, the only stable associations in migratory herds are between a female and offspring.
The blue wildebeest has an unusually restricted breeding season. Around 80 to 90 % of calves are born within a two to three week period, usually at the start of the rains, when conditions are most favourable. This also helps to protect the calves by creating a glut for predators. The female blue wildebeest gives birth annually, to a single calf, after a gestation period of around eight months. The calf follows the female from the moment it can stand, usually within 15 minutes of birth, and is weaned by nine months. The young male is pushed out of the herd by territorial males after the first year, after which it joins a bachelor herd, which may also contain older and non-territorial males. After reaching sexual maturity at three to four years old, the male becomes solitary and attempts to establish its own territory, which may be temporary in migratory populations, or may be continuously occupied and defended for years. Territorial competition between males typically involves ritualised displays, pushing with the horns, and the loud ‘ge-nu’ call that gives the wildebeest its other name, the gnu. The lifespan of the blue wildebeest is around 20 years in the wild.
Migration: Wildebeest are famous for their annual long-distance migration, seemingly timed to coincide with the annual pattern of rainfall and grass growth. The timing of their migration 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, animals quickly move back to their wet season ranges. Every year the animal moves around 3000 kilometer like clock work.
Factors that are 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. One study found that in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content. Wildebeest migration at the large-scale 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.
Factors that are 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. One study found that in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content. Wildebeest migration at the large-scale 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.
Numerous documentaries feature wildebeest crossing rivers, many being eaten by crocodiles or drowning in the attempt. While having the appearance of frenzy, recent research has shown that a herd of wildebeest possesses what is known as “swarm intelligence”, whereby the animals systematically explore and overcome the obstacle as one. Major predators that feed on wildebeest include the lion, hyena, cheetah, leopard, and crocodile, which seem to favour the wildebeest. Wildebeest however are very strong and can inflict considerable injury to even a lion. Wildebeest have an apparent maximum running speed of around 64 km/hr. 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 behaviourally and how much is hard wired into the DNA of the animal. 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. In the Serengeti Ecosystem, Tanzania, wildebeest may help also facilitate the migration of other smaller-bodied grazers, such as Thomson's Gazelles which eat the new growth shoots on grasses that were stimulated by wildebeest foraging.
Zebras and wildebeest group together in open savannah environments when there is a high chance of predation. This grouping strategy reduces predation risk because larger groups decrease each individual’s chance of being hunted, and also because predators are more easily seen in open areas. 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 that along with other ungulates, wildebeests responded more strongly to the baboon alarm calls compared to the baboon contest calls even 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 there was a dispute between two males.
Threat: Although the blue wildebeest is thought to undergo natural periodic population declines due to environmental factors such as drought, the species is also under threat from the spread of human settlement, livestock and agriculture, as well as poaching for meat. If the number of blue wildebeest killed by humans increases as human populations increase, the species could face a permanent decline. However, perhaps the greatest threats are human activities that prevent the blue wildebeest migrating or accessing its seasonal ranges. These include fences, and the elimination of water sources as a result of deforestation and irrigation practices. The dependence of some migratory populations on seasonal access to unprotected areas, where the wildebeest are more vulnerable to poaching and habitat loss, could also result in smaller, resident populations that are confined within protected areas.
Conservation: The blue wildebeest is still widespread and numerous, and occurs in many protected areas throughout its range, including the Serengeti National Park in Tanzania, a World Heritage Site. However, some populations and subspecies are of concern, particularly Connochaetes taurinus albojubatus, which is thought to have undergone large declines. In addition, even within many protected areas the blue wildebeest is already dependent on deliberate management and conservation policies for its survival.
The Serengeti-Masai Mara ecosystem may contain around 70 % of the global population of blue wildebeest, meaning the future of the population here will have a significant impact on the species overall conservation status. As the dominant large herbivore in many of these areas, wildebeest have a major influence on the whole ecosystem. Monitoring and protection of this distinctive antelope may therefore be essential for the conservation of these ecosystems as a whole.
References:
http://www.iucnredlist.org/apps/redlist/details/5228/0
http://en.wikipedia.org/wiki/Wildebeest
http://animals.nationalgeographic.com/animals/mammals/wildebeest/
http://www.awf.org/content/wildlife/detail/wildebeest