Elephants Eat Dirt to Supplement Sodium

Like many large herbivores, African and Asian elephants often seek out natural mineral licks, regions of soil where minerals are concentrated, with important conservation implications. Now data collected by Earthwatch teams that worked in Hwange National Park, Zimbabwe, provides strong ecological, physiological, and behavioral evidence for the function of this behavior.From the Earthwatch:Elephants Eat Dirt to Supplement Sodium

Like many large herbivores, African and Asian elephants often seek out natural mineral licks, regions of soil where minerals are concentrated, with important conservation implications. Now data collected by Earthwatch teams that worked in Hwange National Park, Zimbabwe, provides strong ecological, physiological, and behavioral evidence for the function of this behavior.

In a recent article in the Journal of Mammalogy, Dr. Joseph Dudley and his colleagues investigate the role of geophagy, literally ‘eating dirt,’ by elephants to supplement low sodium levels in food and water supplies. Dudley, currently a conservation specialist working with Headquarters U.S. Army in the Pentagon, was principal investigator of the Earthwatch-supported project The Elephant Factor in 1997 and 1998. He surprised scientists in 1996 with the first-ever published scientific reports of carnivory by hippos, a phenomenon further documented by his Earthwatch teams.

“This work provides insights into the patterns and intensity of mineral lick use by African bush elephants,” said Dudley. “This is an important phenomenon whose physiological and social dimensions merit much further study and elucidation. African forest elephants and Asian elephants in rainforest habitats also seek out and use salt or mineral licks, and there is surprisingly little known about this behavior.”

Scientists have long hypothesized that elephants use salt licks to supplement an insufficient dietary intake of sodium, but conclusive verification has been lacking. The Journal of Mammalogy paper uses several lines of evidence to test the hypothesis, from examining mineral content of available plants and the soils consumed by elephants to observing patterns of salt lick use.

The scientists found that, unlike other minerals, sodium in woody plants and natural water supplies may be inadequate to meet the minimum requirements of elephants. The soils consumed by elephants had higher levels of sodium than other soils in the area, but did not differ in terms of other minerals.

Among the significant findings, female elephants consumed more mouthfuls of soil at salt licks and spent more time feeding on soil than males. This suggests that geophagy is driven by nutritional requirements, which tend to be greater in females due to pregnancy and lactation. The scientists also report that soil-eating is more intense in individuals that had a lower level of sodium in their dung, consistent with a dietary sodium deficiency.

“I believe that this is the first sodium study to link physiology, in the form of sodium loss in dung, with the behavior of soil consumption,” said Ricardo Hold (Princeton University), the lead author of the paper and a former field assistant on The Elephant Factor project. “This is important for management and conservation because it tells us about the habitat and food requirements of elephants.”

Although these findings do not rule out the possibility that elephants use salt licks for some dietary need not measured, they are the strongest support yet for the sodium supplementation hypothesis. The study suggests that sodium supplementation may be an important tool for managing elephant populations and their impact on food resources.