and the predators become more active. Calves weigh about at birth, and can usually stand on their own within a few minutes of birth. To escape predation, calves remain close to their mothers for a significant time, and may continue suckling until the next year's calf is nearly due. Male calves leave their mother at about 8 months and form herds with other male juveniles. In large female herds, 80% of the wildebeest offspring survive the first month, compared to a 50% survival rate in smaller herds. Diseases and parasites The blue wildebeest is susceptible to foot-and-mouth disease, anthrax, sarcoptic mange, and hoof gangrene. The herpesvirus was first isolated from the blue wildebeest in 1960 by veterinary scientist Walter Plowright. Although the causes of death vary from year to year, in one drought in Botswana, young calves and aged females were the most likely to die. On another occasion, an estimated 47% of deaths were caused by disease, 37% were due to predation, and the remainder were the result of accidents. The animal can be host to a number of different parasites. In one study, blue wildebeest were found to be hosts to 13 species of nematodes, one trematode, larvae of five oestrid flies, three species of lice, seven ixodid tick species, one mite, and the larvae of a tongue worm. Of these, most were more prevalent at some times of the year than others. Generally, the larvae of Gedoelstica and Oestrus occur in the nasal passages and respiratory cavities of the blue wildebeest, and sometimes migrate to the brain. Compared to some other bovids, blue wildebeest are resistant to infestations by several species of ticks. Distribution and habitat The blue wildebeest is native to Kenya, Tanzania, Botswana, Zambia, Zimbabwe, Mozambique, South Africa, Eswatini, and Angola. Today, it is extinct in Malawi, but has been successfully reintroduced into Namibia. Blue wildebeest are mainly found in short-grass plains bordering bush-covered acacia savannas in southern and eastern Africa, thriving in areas that are neither too wet nor too arid. They can be found in habitats that vary from overgrazed areas with dense bush to open woodland floodplains. Trees such as Brachystegia and Combretum spp. are common in these areas. Blue wildebeest can tolerate arid regions as long as a potable water supply is available, normally within about distance. The southern limit of the blue wildebeest stops at the Orange River, while the