Utilisation of low density vacuum zones by white rhinos in the Umfolozi Game Reserve.
White rhinos in the Umfolozi Game Reserve (UGR) are managed with a 'Sink Management Policy' which utilises natural dispersal patterns of white rhinos from an area of high density (the core), to areas of low density (vacuum zones). This study was initiated to determine how white rhinos utilised the vacuum zones, as the management staff of the UGR felt that white rhinos were not dispersing into them but utilising them only as areas of trophic resources. Significantly different white rhino densities were established in the Makhamisa and Masinda vacuum zones by removing white rhinos from Masinda. Changes in the density of white rhinos were monitored and the age and sex compositions determined. No significant changes in the density of white rhino groups were recorded during the study, however, the density of individuals in Makhamisa increased significantly in the dry season, while the density in Masinda did not change. The reason for this increase could not be determined, however, the most likely explanation was that rhinos moved toward the Makhamisa study area in search of surface water which was present in the White Umfolozi River. During the dry season the water level in the Umfolozi River was low so the white rhinos where able to cross into the study area. However, owing to the above average rainfall, resources were not limited in either study area, and most likely in most of the reserve. Thus, it could not be determined why white rhinos would need to enter the Makhamisa study area. Changes in grass height, grass colour, and the availability of water in pans and streams were monitored throughout the study. The grassland community compositions of the two study areas were found not to be significantly different. The total utilisation of the different grassland communities by white rhinos during the study were determined for both study areas. White rhinos in the two study areas utilised the grassland communities in a similar pattern throughout the study. During the wet and dry seasons, white rhinos primarily foraged in the short grassland community (Panicum coloratum & Themeda-Urachloa), their staple grassland community, and were not observed to switch and start foraging in the tall grassland community (Themeda & Themeda-Panicum). their reserve community. White rhinos in both study areas were able to forage in their stable grassland community throughout the dry season because of the above average rainfall experienced during the study The results of the study suggest that white rhinos outside the study areas did not utilise the vacuum zones for trophic resources. However, as the study was conducted in a year with above average rainfall, these findings may not represent how white rhinos utilise the vacuum zones in years with average or below average rainfall.