Black wildebeest
Black wildebeest act as hosts to a number of external and internal parasites. A study of the animal in Karroid Mountainveld (Eastern Cape Province, South Africa) revealed the presence of all the larval stages of the nasal bot flies "Oestrus variolosus" and "Gedoelstia hässleri". The first instar larvae of "G. hässleri" were found in large numbers on the dura mater of wildebeest calves, specially between June and August, and these later migrated to the nasal passages. Repeated outbreaks of mange (scab) have led to large-scale extinctions. The first study of the protozoa in blue and black wildebeest showed the presence of 23 protozoan species in the rumen, with "Diplodinium bubalidis" and "Ostracodinium damaliscus" common in all the animals.
Wildebeest
Today, 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. 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, reducing the wildebeest population to less than 10% of its previous size. Illegal hunting is a major conservation concern in many areas, along with natural threats posed by main predators (which include lions, leopards, African hunting dogs, cheetahs and hyenas). Where the black and blue wildebeest share a common range, the two can hybridise, and this is regarded as a potential threat to the black wildebeest.