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.
