SummaryTsavo National Park, in Kenya, probably contains the largest population of black rhinoceros (Diceros bicornis(L.)) left in existence. Large‐scale damage of the vegetation initiated by elephants and aggravated by fire has changed considerable areas of the park. The ecology of the black rhinoceros in this changing environment has been studied; the present status and population structure is considered here, including the development of detailed ageing criteria for the species, an analysis of natural mortality and survivorship, and a record of the structure of the living populations within the major habitat types.Crania and mandibles were collected from 506 rhinoceros found dead in all areas of the park. This material was divided into 20 relative age classes based on dental characteristics. Crude chronological ages, based on an estimate of the maximum expectation of life and the examination of seven known‐age dental records of captive animals, were assigned to each age class. These crude ages were then refined by examination of 16 dental records of known‐age wild rhinoceros, and a chronological age scale established.A survivorship curve of the population was thus constructed. Annual mortality during the first and second year of life is about 16%, and the indicated mean annual mortality from 5–25 y is 9.8%. A theoretical model of the population structure is shown, and analysis of the annual mortality and recruitment at birth suggests that the population was stable during the 1960's. Assuming the data represent a stable population the mean expectation of life at birth is 8.4 y.Thirteen major habitat types are described. The characteristics of the rhinoceros population within each habitat type were established both from ground studies and aerial observations. Nearly 700 rhinoceros were identified and catalogued on the ground, in sample areas selected for intensive study. Population structures, cow: calf ratios, and recruitment appear to be average in most habitat types. The analysis of recruitment at birth and mortality during the first year of life, both from computations from the survivorship curve and from the structure of the living populations, support the validity of the ageing criteria, and further suggest that the population was stable during the 1960's.Finally, the relationship between the elephant and the rhinoceros in the changing environment is discussed with reference to recent findings in elephant ecology. In conclusion it is recommended that population reduction of the Tsavo elephants should be in