| 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 | |
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Connochaetes gnou – black wildebeest |
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The wildebeest (plural wildebeest, wildebeests or wildebai), also called the gnu ( /ˈnuː/ noo or /ˈnjuː/ new)[1] is an antelope of the genus Connochaetes. It is a hooved (ungulate) mammal. Wildebeest is Dutch for "wild beast" or "wild cattle" in Afrikaans (beest = cattle), while Connochaetes derives from the Greek words konnos ("beard") and khaite ("flowing hair").[2] The name "gnu" originates from the Khoikhoi name for these animals, "gnou".
Gnus belong to the family Bovidae, which includes antelopes, cattle, goats, 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 that these two species diverged about one million years ago resulting in a northern and a 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 there are five subspecies of the blue wildebeest while the black wildebeest has no living subspecies.[3] In East Africa, the wildebeest is the most abundant big game species, both in population and biomass.[4]
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A full grown wildebeest can be 4 ft 2 in (1.27 m) to 4 ft 10 in (1.47 m) at the shoulder and weigh 265–600 lb (120–270 kg). 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 30 years, though their average lifespan is around 20 years.[5] The wildebeest have a broad muzzle shaped like a lawnmower which helps it with eating short grass.[4]
The most striking morphological differences between 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, standing taller and weighing more than the black wildebeest.[3] In males, the blue wildebeest stand 150 cm tall at the shoulder and weigh around 250 kg[6] while the black wildebeest stands 111 to 120 cm tall[7] and weighs about 180 kg.[8] In females, the blue wildebeest have a shoulder height of 135 cm and weigh 180 kg[6] while the black wildebeest females stand 108 cm at the shoulder and weigh 155 kg.[8] 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 than downward before curving at the 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 colored fur with a mane that ranges in color from cream to black, and a tail that is cream colored at the end. The blue wildebeest lives in a wide variety of habitats that includes woodland and grassland while the black wildebeest tends to reside exclusively in open grassland areas.[3] The blue wildebeest migrates over long distances in the winter, whereas the black wildebeest does not.[9] The milk of the female black wildebeest contains higher protein, lower fat, and lower lactose content than the milk of female blue wildebeests [10]
In a typical year, wildebeest calves are born within a short period of time (roughly 90% are born in a three week period), presumably as an adaptation to swamp potential predators, like hyenas and lions [11]. Calves born outside of the peak calving period often have a lower survival probability. Immediately after they are born, wildebeest calves start following their mothers. However, these young calves suffer from high mortality and only those with the best genetic endowments and who have experienced mothers survive through the first few years of life.[4]
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 (months later), animals quickly move back to their wet season 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.[4] One study found that in addition to phosphorus, wildebeest select ranges containing grass with relatively high nitrogen content [12]. 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 a frenzy, recent research has shown that a herd of wildebeest possesses what is known as a "swarm intelligence", whereby the animals systematically explore and overcome the obstacle as one.[13] Major predators that feed on wildebeest include the lion, hyena, cheetah, leopard, and crocodile, which seem to favor the wildebeest.[5] 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/h (40 mph).[14] 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 behaviors, such as animals taking turns sleeping while others stand guard against a night attack by invading predators. Scientists are unsure how much is learned behaviorally 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.[15]. In the Serengeti Ecosystem, Tanzania, wildebeest may help also facilitate the migration of other smaller-bodied grazers, such as Thomson's Gazelles (Eudorcas thomsonii) who 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.[16]
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.[17]
Due to their migratory ways, the wildebeest do not form permanent pair bonds or defend a set territory. The wildebeest mating season is called rut, and during this time the males establish temporary territories and try to attract females. These small territories are about 3000 square meters, with up to 300 territories in a square kilometer. The males defend these small territories from other males while trying to lure in 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.[4] The mating season usually occurs between May to July and the birthing period usually takes place between January to March, at the start of the wet season. The gestation period is about 8 to 9 months, and the average estrous cycle is about 23 days. Wildebeest females breed seasonally and ovulate spontaneously.[18] Groups of wildebeest females and young live in the small areas established by the male. When groups of wildebeest join together, there is a larger female to male ratio as the females flock to the areas held by fewer males.[16] It has also been suggested that this female dominated sex ratio may be due to illegal hunting and human disturbance. Higher male mortality has been attributed to illegal hunting.[19]
Due to their confinement in small areas in South Africa, the two species of wildebeest, the black wildebeest and the blue wildebeest have interbred, resulting in fertile hybrid young. These two species are brought into close contact with each other on game farms and reserves in South Africa. The resulting hybrid young may include characteristics of both species and even some intermediate traits. The hybrids also tended to have strange dental, horn, and skull shapes.[3]
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. Over-land migration as a biological process requires large connected landscapes, which is increasingly difficult to maintain, particularly over the long-term, when there are competing human demands on the landscape 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 kilometers 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 ten percent of its previous size [20]. Wildebeest migrations in the Serengeti and Tarangire Ecosystems, Tanzania, are also threatened by the construction of a roadway across the northern portion of these ecosystems. 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 that 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 migrate 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 Esotha National Parks.[4].
Wildebeest are killed for food, especially for biltong in Southern Africa, which is dried game meat. Biltong is a delicacy and an important food item in Africa.[4] It has been found that the meat of females is more tender than that of males, and that meat was the most tender during the autumn season.[9] Wildebeest are a regular target for illegal meat hunters because they are relatively easy for hunters to kill. When preparing the wildebeest, the carcass is usually cut into 11 pieces. The estimated price for wildebeest meat is about US$ 0.47 per kilogram.[21]