For African elephants, currently the largest land animals walking the Earth, finding food efficiently is critical to survival. These endangered pachyderms must eat upwards of 330 pounds of low-calorie vegetation per day to sustain themselves. Yet how they find the best ways to get their greens remains elusive. Data from more than 150 elephants found that they plan their journeys based on both resources availability and energy costs. The findings are detailed in a study published March 26 in the Journal of Animal Ecology and show how every step matters for these gentle giants.
“These new results have important implications for assessing and planning conservation and restoration measures, such as dispersal corridors, by explicitly accounting for the energy costs of moving,” Emilio Berti, a study co-author and ecologist from the German Centre for Integrative Biodiversity Research (iDiv) and Friedrich-Schiller-University Jena said in a statement.
Every step you take
The International Union for Conservation of Nature (IUCN) lists the African forest elephant (Loxodonta cyclotis) as Critically Endangered and the African savanna elephant (Loxodonta africana) as Endangered. Increased human activity has further fragmented their habitats, so understanding how they move throughout their landscape is crucial for designing better conservation strategies. They can travel between 31 and 121 miles in a single day, yet the key drivers behind elephant movements across this often harsh terrain have been less clear.
In this new study, scientists from the University of Oxford in the United Kingdom, iDiv, and Friedrich Schiller University Jena in Germany used GPS tracking data from 157 African elephants in northern Kenya. The data was collected by conservation organization Save the Elephants from 1998 to 2020.
The data indicated that the elephants strongly prefer landscape with lower movement costs. About 94 percent of the elephants in the study avoided rough terrain and steep slopes. According to the team, this suggests that the animals are aware of their surroundings and are making cost-benefit decisions regarding the most energy-efficient paths to take.
The elephants also actively select areas that have higher vegetation productivity. Ninety-three percent indicated a preference for going towards more resource-rich environments.
Similarly, water sources play a key role in where they choose to go. However, individual elephants can respond to water differently. Some will stay nearby, while others roam further away. This indicates that their movement choices are much more complex than simply traveling over to the nearest body of water.
As far as speed, elephants moving at a slow speed show an even stronger avoidance of the difficult, more energetically-costly terrain. About 74 percent of the individual elephants avoided these rough or steep areas when moving slowly. This number jumped to 87 percent when they moved at intermediate speeds and 93 percent when moving fast. The elephants appear to be carefully balancing both effort and energy efficiency on long journeys.
According to the team, this behavior is comparable to birds that appear to deliberately use favorable thermal uplifts to reduce the energetic costs of flying.
Enter ENERSCAPE
In order to analyze the tracking data, the team used a modelling method called ENERSCAPE. The program estimates the energy costs of movement based on the animals’ body mass and the slope of the terrain. By integrating these estimates with satellite data on the vegetation productivity and water availability in the area, the team built detailed energy landscapes that can help better explain elephants’ decisions regarding where to move.
A statistical approach called step-selection functions was also used to assess how these particular elephants selected which paths to take. This technique compares the locations that the elephants actually visited with other nearby areas they could have selected, but ultimately, did not. By doing so, the team pinpointed which environmental factors likely play a role in elephants’ movement decisions and habitat selection.
[ Related: African elephants use name-like calls to address each other. ]
‘Save energy whenever possible’
These new findings could help conservationists design protected areas and migration corridors to reduce conflict with humans. Additionally, the team suggests that conservation strategies should account for these individual differences in habitat preferences, particularly regarding water access.
Understanding these results could also help predict how elephant movements may respond to climate change. Increased temperatures and changes to rain patterns affects both the energy costs of moving, and the availability of food and water.
In future studies, the team aims to refine energy landscape models by adding seasonal changes, human disturbances, and the impact of climate change on elephant movements into their models.
“While more detailed research is needed to fully understand how an elephant uses its habitat, this study identifies a central decision-making factor for travelling elephants,” study co-author and University of Oxford evolutionary biologist Fritz Vollrath said in a statement. “Save energy whenever possible.”
More deals, reviews, and buying guides
