Population ecology of Oribi in Serengeti National Park, Tanzania

The population ecology of oribi (Ourebiaourebi Zimmermann 1783) in Serengeti National Park, Tanzania was studied between October 1988 and November 1989. Two main objectives of the study were: (1) to establish the abundance of oribi, and (2) to investigate what factors regulate the population. Four aspects were considered. (1) Abundance .Three methods were used to estimate oribi numbers in northern Serengeti. The density of oribi was estimated to be 8.02 km-2 from known individuals, which is comparable to 9.59 ± 2.83 (95% C.L.) by road transacts. The total population in the census zone (700 km2) was estimated to be 5986 ± 1086 (95% C.L.). Biases in counting small antelopes in savanna woodlands are discussed. (2) Habitat selection and ungulate associations were recorded along transacts traversed by vehicle. The frequency with which different habitats and ungulate species were encountered was measured from records at systematic points. This generated expected frequencies to compare with observed frequencies of oribi in these habitats. Oribi preferred rocky outcrops and Combretum Terminalia woodlands, and grasses and shrubs in these woodlands. Oribi associated with impala, kongoni and topi. This provided evidence in favour of predatrion as a regulating factor. (3) Activity pattern. Oribi were diurnal with some nocturnal feeding. They spent most of the time lying down (52%) and feeding (43%), standing contributing only 5%. More feeding took place (a) in the dry season, (b) under cloudy skies, and (c) in moonlight. (4) Food selection. The availability of food plants was determined from line transects. Feeding individuals were studied by direct observation. Oribi were primarily grazers and selected for both plant species and plant parts. They preferred some grass species and annual legumes. They avoided theme datriandra. Selected food plants were chemically analysed. Browse materials had higher values of crude protein than grasses. However, browsing was predominant only during the dry season when grass quality was poor. (5) In conclusion, both food supply and predation appeared as important limiting factors.