The Ecology and Behaviour of the Common hippopotamus, Hippopotamus amphibious L. in Katavi National Park, Tanzania: Responses to Varying Water Resources
Katavi National Park (KNP) is a stronghold for hippopotami in Tanzania. To predict the probable effects of future changes in water availability, annual variations in rainfall, river level, river discharge, ground water levels and the lateral extent of swamps used by hippopotami, were related to annual variations in their behaviour, distribution and abundance in aquatic shelter sites. Rainfall did not change consistently between 1950 and 2010. In contrast river levels and flow decreased over between 1990 and 2010. It is concluded that these reductions have been caused by an increase in irrigation of rice fields increasingly planted in upstream regions of the catchment area. Rainfall fell in a pronounced annual cycle. The wet season started in December, increased in January, decreased in February reaching an annual peak in March. The dry season lasted from May to November. Variation in height, biomass and greenness of ground layer swards used by feeding hippopotami, closely mirror this annual pattern of rainfall. As the dry season progresses hippopotami become increasingly aggregated in remaining aquatic shelter sites by day, to wallow and thermoregulate with concomitant depletion of the nocturnal feeding grounds close to remaining shelter sites. Five observation sites were chosen, representing a gradient in the amount of water persisting through the dry season. Hippopotami showed spatial differences in their activity budgets and the frequency of behavioural events at these sites, which were consistent with the way they responded to variation in water availability between seasons. Extrapolating these findings to predict responses to future changes in global climate and land use, I conclude consistent implementation of existing national laws governing diversion of water from rivers up-stream of the park will be crucial for maintaining vigorous populations of hippopotami in KNP. Similar problems of a catchment area scale occur in other National Parks in Africa.
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