Ecology of waterbuck Kobus Ellipsiprymnus (Ogilby, 1833) in the Umfolozi Game Reserve

Abstract

Between 1970 and 1975 Natal Parks Board hel .icopter counts of waterbuck ( Kobus ellipsiprymnus) in the Umfolozi Game Reserve (UGR) declined from 1 098 to 494. The purpose of this project was to study the ecology of waterbuck with an emphasis on population regulating mechanisms, so that the reality and significance of this decline could be assessed. Density estimates for 1976-1977 were over twice the 1976 helicopter count of 319, but the population was confirmed to be declining. The ecological density of waterbuck represented 11,9 per cent of the metabolic biomass of grazers, which compared well with data from other areas. However, the other species' proportionate contributions to biomass were far from optimal, with an excess of short grass feeders. High juvenile mortality (80,7 per cent), attributable mainly to severe tick (Rhipicephalus appendiculatus) infestations, was the principal cause of the present decline. These severe infestations were probably symptomatic of poor condition of the whole waterbuck population, which meant that the ultimate cause of juvenile mortality lay elsewhere. The hypothesis that the waterbuck population was in a stressed condition was supported by their habitat utilization patterns, their feeding ecology and aspects of their behaviour. The dynamics of interspecific associations suggested that the primary habitat of Waterbuck was that now occupied by nyala (Tragelaphus angasi) and what had been recorded were the results of competition pushing waterbuck into an unfavourable habitat. Feeding studies indicated that nutritious food for herbivores represented a limited resource in UGR during winter, for which waterbuck may be largely outcompeted and that nyala and impala ( Aepyceros melampus) were the rnain competitors . Interspecific competition was the probable ultimate cause of the decline of waterbuck in UGR. It was recommended that the numbers of nyala and impala be reduced and that this action be integrated into a more precise management plan for UGR than exists at present.