Tsavo NP was gazetted as a national park in 1948. The reason for this was that it was the only large tract of land that was virtually uninhabited by man because of the presence of several species of tsetse fly, and comparatively low rainfall resulting in an uneven distribution of permanent water.
In 1948, rhino were particularly numerous and probably constituted the largest single concentration in Africa. Drought and degradation of habitat by elephant during 1960 and 1961 resulted in the death of at least 300 rhino.
It was noticed that many of the rhino had extensive black patches on their sides which microscopic examination showed to be a thin film of dried blood. At first it was thought that it may have been caused by heavy infestations of biting flies, Luperosia sp., and another as yet unidentified muscid. Both these flies were found breeding in rhino faecal middens. Efforts have been made to breed them in the laboratory with varying degrees of success, and studies at Voi have revealed that under optimum conditions the muscids appear to have an 18-day breeding cycle. More recent studies of the blood films, however, indicate that the black patches may not be caused solely by biting flies and emphasize the need for further research. Collections of intestinal parasites from rhino have been made and it was shown that a species of Microfilaria is associated with the sores commonly found on the chest and flanks of rhino.
