Population characteristics and management of black rhinoceros Diceros bicornis minor and white rhinoceros Ceratotherium simum simum in Ndumu Game Reserve, South Africa

The population sizes, sex and age structures, home range sizes and overlap were determined for black rhinoceros Diceros bicornis minor and white rhinoceros Ceratotherium simum simum in Ndumu Game Reserve by repeated sightings of known individuals and groups. The black rhino population in June 1986 was estimated to be 42, of which 10% were juveniles and with an adult sex ratio not differing significantly from parity. Their home range varied between 4·3 km 2 for a mixed group of animals and 13·8 km 2 for an adult female with calf. Home range overlap varied from 12 to 80%. The white rhinoceros population in June 1986 was estimated to consist of 57 animals of which 14% were juveniles. Adult sex ratio did not differ significantly from parity. Home range size varied from 2·5 to 22·9 km 2 and overlapped extensively for both sexes. Both populations of rhino in Ndumu are below the proposed minimum effective population size of 50. Consequently, for both species we recommend that in conjunction with the sustained removal of animals from the population, individuals from the parent populations should be periodically introduced into the reserve to increase the effective population size.