Where Elephants Go When It’s Raining
Elephant Distribution in Zambia
Background
African elephants (Loxodonta africana) are nomadic creatures, traveling thousands of miles annually to find basic resources like food and water. Elephant diets change with the season in Africa. During the dry season in Zambia, for instance, elephants prefer to forage for leaves among the trees, but during the wet season, they eat mainly grasses — and this is where the nomadic lifestyle kicks in. Once the wet season begins, elephants must disperse to areas that have enough nutrients to support them.
Scientists are now tackling the uncertainty surrounding where elephants prefer to live during Zambia’s wet season, and the routes they take to get there. The routes from their suitable habitats during the dry season to their wet season habitats are called corridors. Forest fragmentation, often caused by humans, can negatively affect these passages.
Corridors are necessary not only to connect wet and dry season habitats, but they also prevent different elephant populations from becoming isolated. These different populations, otherwise known as metapopulations, can interact with each other and expand each other’s gene pools to prevent inbreeding. Knowing where habitats and corridors occur can better preserve the African elephants.
Summary
Scientists determined the suitable wet season habitats for African elephants in the Zambian Sioma Ngwezi National Park and identified which corridors the elephants took as passageways. With the Zambian elephant populations significantly diminished due to poor law enforcement and subsequent poaching, this information helps target areas that need better supervision. In all, there were 15 suitable habitats identified with 24 corridors to reach them. This data was found using GPS telemetry to track the elephants, and different geographic information system (GIS) tools to map things like elevation and forested regions.
The scientists noted that the elephants chose corridors based on land cover, elevation, and vegetation. They were most likely to be found in forested areas without civilization, preferring elevations of 990 meters to 1,020 meters. The African elephants seemed to have adapted enough to human activity that proximity to human settlements or roads did not affect the elephants’ movement across Zambia, though they tended to travel on undeveloped land more. By protecting and restoring corridors, the movement of elephants away from human settlement would naturally be encouraged, resulting in fewer negative elephant-human interactions.
GPS telemetry was used by the scientists as a form of tracking animals with GPS radio collars. For this study, 8 elephants were tracked for 6 months on an hourly basis. This created ample points to show elephant movement over time. Points could then be combined with images captured by satellites showing the Zambian landcover. A specialized software called ENVI classified the landcover into four different types — human-developed areas, forests, open water, and wooded grasslands — and showed elephants in forested areas more often than others.
When utilizing different GIS software as mapping tools, many maps are made up of thousands of pixels which form a raster dataset. Each raster dataset makes up a different layer on the map. For example, in this study a raster dataset was used to create a topography layer that showed the shape and elevation of the Zambian landscape, as well as a layer showing water flow and a separate layer showing soil moisture. Though water levels did not sway elephant travel as much, elevation played a significant part in which corridors elephants used.
As stated in the study, the elephants preferred elevations from 990 m — 1,020 m above sea level. Though further research is needed to know why elephants remained at these lower elevations, it is most likely to avoid spending too much energy on steep terrain. These lower elevations probably also provide habitats for plants specific to elephant diets.
A vegetation map layer (normalized difference vegetation index) was created by looking at the amount of infrared light shown on the satellite imagery. Since infrared light is reflected by vegetation, this was an easy way to see where vegetated areas exist. This gave the scientists an idea of where the elephants would travel, since the megafauna are able to use their olfactory cues, or sense of smell, to identify vegetated routes that have the best food selection.
Lastly, a linkage mapper technique was used, which included a circuit theory and a least cost path. Both techniques use the data from the different layers, including the data from the elephants’ GPS collars. Circuit theory shows the flow of movement for a specific species, and the least cost path shows areas with less resistance to elephant movement. These areas act as the least energetically taxing places for the elephants to live, with the most ideal landcover, elevation, and vegetation. The data is simplified, or reclassified, as a physical representation displaying areas with a higher probability to act as elephant habitat.
Elephants have been in danger due to poaching, and have actually been a danger to local people. Because of this study, areas highlighted by the linkage mapper technique can be better protected, and areas at the elephants’ preferred elevations can be reforested to create more natural corridors and reduce human-elephant conflict. Overall, diminishing human contact helps achieve the goal to enhance elephant populations as important cultural icons to the people of Zambia for years to come.
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