Learn the surprising culprit limiting the abundance of Earth’s largest land animals
Humans live in a world abundant in salt, but this everyday seasoning is a luxury for wild herbivores, and it’s far from clear how these animals get enough.
A new study published today in Nature Ecology and Evolution and authored by Northern Arizona University researchers and collaborators found the density and distribution of Earth’s largest land animals, including elephants, giraffes and rhinos, appear to be limited by this kitchen essential. There are only a few areas in the world where these large animals can get enough sodium from the local flora to survive.
“In Africa, sodium availability varies over a thousandfold in plants,” said Andrew Abraham, lead author of the study, a research associate at City University of New York and NAU alumnus. “This means that in many areas, wild herbivores simply cannot get enough salt in their diet.”
This is true to some extent for all herbivores—most plants don’t need salt and often contain trace amounts of it—but it’s especially pronounced for megaherbivores. Previous research had suggested that sodium deficiency increases with body size. Using a totally separate methodology, this study reached the same conclusion.
Mapping the missing megaherbivores
The authors combined their high-resolution maps of plant sodium with databases of animal dung and density measurements. Dung can tell scientists a lot about animals, including whether they’re getting enough salt. They connected areas with salt limitation to lower numbers of larger herbivores.
It’s not just about ability to survive, though. Salt limitation explains several interesting behaviors exhibited by wild animals.
“In Kenya, elephants enter caves to consume the sodium-rich rocks and in the Congo rainforest, they dig for salt in riverbeds,” Abraham said. “Gorillas are known to fight for the saltiest foods, while rhinos, wildebeest and zebra often gather at salt pans from the Kalahari Desert to the Maasai Mara.”
This study also offers a new explanation for the “missing” megaherbivores.
“West Africa is a very productive region, but there aren’t many megaherbivores there,” said Chris Doughty, a professor of ecoinformatics at NAU. “We think that a lack of sodium, likely combined with other factors such as overhunting and soil infertility, plays an important role in limiting their numbers.”
This research raises a number of conservation concerns. Many protected areas are located in low-sodium environments, and humans have created artificial sodium hotspots through various activities like borehole pumping and road salting.
“If animals can’t get enough sodium in their natural habitats, they may come into conflict with people on their quest to satisfy their salt hunger,” Abraham said.
Journal
Nature Ecology & Evolution
Article Title
Sodium constraints on megaherbivore communities in Africa
Article Publication Date
9-Dec-2025
Elephants, giraffes and rhinos go where the salt is
Herbivores require a steady intake of sodium to keep their metabolism running smoothly. This is why farm animals have long been given salt or mineral licks. Animals in the wild, however, need to get their salt from sources in their habitats. In some areas, plants and other natural sources of salt provide sufficient sodium, while in others sodium levels are scarce. These differences can influence where certain species settle or how far they will migrate to find natural salt licks.
A new study conducted in collaboration with the University of Zurich now shows that in many places the largest herbivores in the wild – elephants, giraffes and rhinos – have limited access to sodium. The researchers combined high-resolution maps of plant sodium with data on the animals’ population density and with results of fecal analyses. Since sodium deficiency is directly detectable in the feces, they were able to draw conclusions about the species’ actual sodium intake.
The larger the body, the greater the risk
“Plant sodium availability varies by a factor of 1,000 across sub-Saharan Africa,” says Marcus Clauss, co-director at the University Animal Hospital at UZH and co-author of the study. “In some areas, wild herbivores are simply unable to get enough salt through their food.”
However, not all herbivores are equally affected. The researchers found that sodium scarcity is particularly common among larger-bodied species, or megaherbivores. Their study confirms previous findings that the risk of sodium scarcity increases with body size.
Sodium shortage affects habitat selection
The study also explains certain wildlife behaviors. “In Kenya, for example, elephants enter caves to reach sodium-rich rock, while in the Congo they dig for salt in riverbeds. And this behavior isn’t limited to elephants. Gorillas fight over particularly salty foods, and rhinos, wildebeest and zebras often congregate at salt pans in the Kalahari Desert,” says first author Andrew Abraham of Northern Arizona University.
The study also provides a new explanation for the scarcity of megaherbivores in West Africa, a region rich in vegetation and species but where megaherbivore numbers are low. The researchers suspect that sodium deficiency plays a central role in the low numbers observed, likely in combination with other factors such as overhunting or poor soil fertility.
Potential conflicts
The researchers also point to key issues for nature conservation. “In areas populated by humans, artificial sodium hotspots are created by boreholes or – in northern parts of the world – by road salting. However, since many protected areas are located in regions that are low in sodium, animals that travel long distances in search of salt could come into conflict with humans more frequently in the future,” explains Clauss.
Journal
Nature Ecology & Evolution
Method of Research
Meta-analysis
Subject of Research
Animals
Article Title
Sodium constraints on megaherbivore communities in Africa, Nature Ecology & Evolution
Article Publication Date
9-Dec-2025
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