Local elephant movements, turning angles, and water access across a rainfall gradient in Southern Africa

Abstract

In the wet season of southern Africa's savannahs, surface water is extensive, allowing elephants to move widely. However, when surface water is restricted in the dry season, elephant use of the landscape is highly dependent on water availability and varies across the southern African region due to an aridity/rainfall gradient and different levels of supplementary provisioning of water. Movement analyses of elephants in the Kruger National Park (KNP), where water sources are mapped in detail, revealed that elephants make high turn angles at water sources; that is, they at least partially retrace the route taken to the water source. This insight allows us to posit water sources in other places where water sources are not adequately mapped and to ask whether elephant movements indicate that they find water easily (while roaming), or whether they must change direction to encounter water. Put simply, is water a waypoint or the destination?

Using high-resolution satellite imagery, and data for 101 collared elephants in six reserves, we studied a west to east rainfall gradient from Namibia to South Africa. We used a quasi-experimental approach to compare protected areas along the rainfall gradient with highly supplemented water against areas with little or no water supplementation. Three patterns emerged from the analysis of the movement data. First, along rivers, where one might have expected widespread, ready access to water, there are particular, favoured destinations, suggesting that elephants use some places along rivers more than others, or that accessible water is not widely available. Second, along apparently dry riverbeds, elephants were able to access water. Finally, movement data uncovered water sources away from rivers where GIS layers on water availability are unavailable or incomplete.

Our results further indicate that some protected areas have so many artificial water holes that they become waypoints — places that do not require unusual deviations from their roaming directions, allowing elephants to access food across wide areas during both wet and dry seasons. Where accessible water sources are few, elephant use is localised and intense, impacting surrounding vegetation.