Establishing the causes of the roan antelope decline in the Kruger National Park, South Africa

Between 1986 and 1993, the roan antelope Hippotragus equinus population in the Kruger National Park, South Africa, declined from about 450 to ca.45 an imals. Data from long term monitoring of herbivore numbers, sex, age and he rd structure and of vegetation condition, supported by spatial and demograp hic modelling and predator sighting records, were used to evaluate potentia l causes of the population decrease, including: (1) competition from zebra and wildebeest, which moved into the roan's range after the introduction of waterpoints; (2) increased predation following the influx of zebra and wil debeest; (3) habitat deterioration due to an extended period of low rainfal l; (4) outbreaks of the disease anthrax; and (5) stress associated with imm unisation against anthrax. Evidence did not support the latter two causes. Drought alone was inadequate as an explanation, although progressive desicc ation over a sequence of low rainfall years, and resultant grassland deteri oration, may have been contributory. Grassland recovery may have been suppr essed by grazing pressure from zebra and wildebeest. The population crash w as associated with an increase in adult mortality, but little apparent chan ge in calf survival, suggesting that nutritional factors were not the prime cause. Increased predation on adult roan due to a build-up in lion numbers , following the zebra and wildebeest influx, seemed to be the proximate cau se of the initial sharp decline in the roan population. However, the ultima te cause was the provision of numerous artificial waterpoints in the roan r ange, which attracted the influx of zebra and wildebeest, particularly duri ng drought conditions. Following the closure of waterpoints in a section of the roan range, the roan herds in the vicinity are recovering. Deficiencie s in current monitoring programmes in the Kruger Park are identified. (C) 1 999 Elsevier Science Ltd. All rights reserved.