In East Africa, the blue wildebeest is the most abundant big game species and some populations perform an annual migration to new grazing grounds but the black wildebeest is merely nomadic. Breeding in both takes place over a short period of time at the end of the rainy season and the calves are soon active and are able to move with the herd. Nevertheless, some fall prey to large carnivores. Wildebeest often graze in mixed herds with zebrawhich gives heightened awareness of potential predators. They are also alert to the warning signals emitted by other animals such as baboons. Wildebeest are a tourist attraction but compete with domesticated livestock for pasture and are sometimes blamed by farmers for transferring diseases and parasites to their cattle. Some illegal hunting goes on but the population trend is fairly stable and some populations are in national parks or on private land. The International Union for Conservation of Nature lists both as least-concern species.
Taxonomy and Evolution Edit
The wildebeest, or the genus Connochaetes, is placed under the family Bovidae and subfamily Alcelaphinae, where its closest relatives are the hartebeest (Alcelaphus spp.), the hirola (Beatragus hunteri) and species in the genus Damaliscus, such as the topi, the tsessebe, the blesbok and the bontebok. The name Connochaetes was given by German zoologist Hinrich Lichtenstein in 1814. Wildebeest were first discovered about 1700 by Dutch settlers on their way to the interior of South Africa. Due to their resemblance to wild cattle, these people called them "wild ox" or "wildebeest". The black wildebeest was first known to westerners in the northern part of South Africa a century later, in the 1800s.
In the early twentieth century, one species of the wildebeest, Connochaetes albojubatus, was identified in eastern Africa. In 1914, two separate races of the wildebeest were introduced, namely Gorgon a. albojubatus ("Athi white-bearded wildebeest") and G. a. mearnsi ("Loita white-bearded wildebeest"). However, in 1939, the two were once again merged into a single race, Connochaetes taurinus albojubatus. In the mid-twentieth century, two separate forms were recognised, Gorgon taurinus hecki and G. t. albojubatus. Finally two distinct types of wildebeest – the blue and black wildebeest – were identified. The blue wildebeest was at first placed under a separate genus, Gorgon, while the black wildebeest belonged to the genus Connochaetes. Today they are united in the single genus Connochaetes: the black wildebeest being named (C. gnou) and the blue wildebeest, (C. taurinus).
According to an mitochondrial DNA 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. A divergence rate of approximately 2% has been calculated. The split does not seem to have been driven by competition for resources but instead by the fact that each species adopted a different ecological niche and occupied a different trophic level.
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. 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. Today, five subspecies of the blue wildebeest are recognised while the black wildebeest has no named subspecies.
Genetics and Hybrids Edit
The diploid number of chromosomes in the wildebeest is 58. Chromosomes were studied in a male and a female wildebeest. In the female, all except a pair of very large submetacentricchromosomes 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.
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. 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. Another study reported an increase in the size of the hybrid as compared to either of its parents. In some animals, the tympanic part of the temporal bone is highly deformed and in others the radius and ulna are fused.
Differences between species EditBoth species of wildebeest are even-toed, horned, greyish-brown ungulates resembling cattle. Males are larger than females and both have heavy forequarters compared to their hindquarters. They have broad muzzles, Roman noses, shaggy manes and tails. 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, while the black wildebeest stands 111 to 120 cm tall and weighs about 180 kg. In females, blue wildebeest have a shoulder height of 135 cm and weigh 180 kg while black wildebeest females stand 108 cm at the shoulder and weigh 155 kg. 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 bluish sheen. The black wildebeest has brown-coloured hair, with a mane that ranges in color from cream to black, and a cream-coloured tail. 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. In some areas the blue wildebeest migrates over long distances in the winter, whereas the black wildebeest does not. The milk of the female black wildebeest contains a higher protein, lower fat, and lower lactose content than the milk of the blue wildebeest. Wildebeest can live more than forty years, though their average lifespan is around twenty years.
Distribution and Habitat Edit
Wildebeest inhabit the plains and open woodlands of parts of Africa south of the Sahara. The black wildebeest is native to the southernmost parts of the continent. Its historical range included South Africa, Swaziland and Lesotho, but in the latter two countries it was hunted to extinction in the 19th century. It has now been reintroduced to them and also introduced to Namibia where it has become well established. It inhabits open plains, grasslands and Karoo shrublands in both steep mountainous regions and lower undulating hills at altitudes varying between 1,350 and 2,150 m (4,430 and 7,050 ft). In the past, it inhabited the highveld temperate grasslands during the dry winter season and the arid Karoo region during the rains. However, as a result of widespread hunting, it no longer occupies its historical range or makes migrations, and is now largely limited to game farms and protected reserves.
The blue wildebeest is native to eastern and southern Africa. Its range includes Kenya, Tanzania, Botswana, Zambia, Zimbabwe, Mozambique, South Africa, Swaziland and Angola. It is no longer found in Malawi but has been successfully reintroduced into Namibia. Blue wildebeest are mainly found in short grass plains bordering bush-covered acacia savannas, thriving in areas that are neither too wet nor too dry. They can be found in habitats that vary from overgrazed areas with dense bush to open woodland floodplains. In East Africa, the blue wildebeest is the most abundant big game species, both in population and biomass. It is a notable feature of the Serengeti National Park in Tanzania, the Maasai Mara National Reserve in Kenya and the Liuwa Plain National Park in Zambia.
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. 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. In the Maasai 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 diminishing area of grazing land as a result of changes in agricultural practices, and possibly fluctuations in rainfall.
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 wet 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. One study found, in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content.
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. 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 even to a lion. Wildebeest have a maximum running speed of around 80 km/h (50 mph). 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. 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 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 Edit
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.
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.
Breeding and Reproduction Edit
Wildebeest do not form permanent pair bonds and during the mating season, or rut, the males establish temporary territories and try to attract females into them. These small territories are about 3000 m2, with up to 300 territories per km2. The males defend these territories from other males while competing for females that are coming into season. The males use grunts and distinctive behaviour to entice females into their territories. Wildebeest usually breed at the end of the rainy season when the animals are well fed and at their peak of fitness. This usually occurs between May and July, and birthing usually takes place between January and March, at the start of the wet season. Wildebeest females breed seasonally and ovulate spontaneously. The estrous cycle is about 23 days and the gestation period lasts 250 to 260 days. The calves weigh about 21 kg (46 lb) at birth and scramble to their feet within minutes, being able to move with the herd in a matter of days. 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 higher because the females choose to move to the areas held by a smaller number of males. This female-dominated sex ratio may be due to illegal hunting and human disturbance as higher male mortality has been attributed to hunting.