Black wildebeest
Features necessary for defending a territory, such as the horns and broad-based skull of the modern black wildebeest, have been found in their fossil ancestors. The earliest known fossil remains are in sedimentary rock in Cornelia in the Orange Free State and date back about 800,000 years. Fossils have also been reported from the Vaal River deposits, though whether or not they are as ancient as those found in Cornelia is unclear. Horns of the black wildebeest have been found in sand dunes near Hermanus in South Africa. This is far beyond the recorded range of the species and it has been suggested that these animals may have migrated to that region from the Karoo.
Blue wildebeest
The blue wildebeest is preyed on by lions, leopards, African wild dogs, and hyenas, and predation is the main cause of death. They are also prone to outbreaks of disease, which may also lead to a decline in numbers. Major human-related factors affecting populations include large-scale deforestation, the drying up of water sources, the expansion of settlements and poaching. Diseases of domestic cattle such as sleeping sickness can be transmitted to the animals and take their toll. The erection of fences that interrupt traditional migratory routes between wet and dry-season ranges have resulted in mass death events when the animals become cut off from water sources and the areas of better grazing they are seeking during droughts. A study of the factors influencing wildebeest populations in the Maasai Mara ecosystem revealed that the populations had undergone a drastic decline of around 80% from about 119,000 individuals in 1977 to around 22,000 twenty years later. The major cause of this was thought to be the expansion of agriculture, which led to the loss of wet-season grazing and the traditional calving and breeding ranges. Similarly, drastic declines have recently occurred in the Tarangire wildebeest migration.