Black wildebeest the hybrid as compared to either of its parents. In some animals, the auditory bullae are highly deformed, and in others, the radius and ulna are fused. Black wildebeest are sexually dimorphic, with females being smaller in size and more slender than males. The head-and-body length is typically between . Males reach about at the shoulder, while females reach . Males typically weigh and females . A distinguishing feature in both sexes is the tail, which is long and similar to that of a horse. Its bright-white colour gives this animal the vernacular name of "white-tailed gnu", and also distinguishes
Wildebeest mortality of calves may be as high as 50%. However, in larger aggregations, or small groups living near large herds, survival rates may be over 80%. 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, with higher male mortality having been attributed to hunting. Today, many wildebeest populations are experiencing rapid declines.