Rwanda's gorillas have found where to find their sodium dose – but it's dangerous

The conservation of mountain gorillas in Rwanda is a great success. A number of extreme conservation measures – such as daily surveillance and protection, veterinary interventions, and controlled ecotourism – have allowed the population to rebound from the precarious trough of the 1960s and 1970s caused by the destruction of habitat and habitat. poaching.

But the population remains fragile. Today, only about 1,000 mountain gorillas live in two isolated populations: one in the Virunga volcanoes – straddling the borders of Rwanda, Uganda and the DRC – which has passed from 250 to 600 individuals in about 30 years; and a group in Uganda's Bwindi National Park with about 400 people.

The survival of this particular species is important for several reasons. First, mountain gorillas are one of our closest living relatives. They can therefore help us understand the evolution and the human behaviors. Secondly, they play an important role in maintaining the health of tropical forest ecosystems – for example by dispersing seeds. Finally, they are a tourist attraction that generates revenue for Rwanda and supports conservation activities throughout the country. In the last two years, tourism has provided over 400 million US dollars to the national economy.

In the Volcanoes National Park of Rwanda, gorillas have left the boundaries of the protected area to sack crops – like eucalyptus and bamboo – on agricultural plots nearby. Leaving protected areas is a huge risk to their safety.

My colleagues from the Karisoke Research Center and the Max Planck Institute of the Dian Fossey Gorilla Fund, and myself, wanted to understand why gorillas were heading to cropland outside protected areas. We found that when the gorillas left the national park, they often went directly to eucalyptus trees. Our nutritional analyzes have shown that eucalyptus is more than one hundred times as rich in sodium as the staple diet of gorillas in the park.

This led us to conclude that sodium was the main incentive for gorilla escapades. All the plants inside the park are low in sodium, with the exception of two species that grow near the top of the volcanoes.

For the sake of sodium

We measured sodium content in samples of 34 of the main gorilla foods and quantified the sodium intake of 22 gorillas from three social groups over a year.

Gorillas consume up to two-thirds of their sodium when they consume eucalyptus.

Sodium is a trace mineral that is crucial for physiological processes, such as muscle and nerve function and the maintenance of fluid levels in various parts of the body.

Sodium deficiency can affect bone, growth and reproduction. A sodium deficiency can trigger a specific hunger that forces animals to do everything in their power to obtain it.

This is true for both gorillas and humans.

It is possible that gorillas eat eucalyptus for other reasons. Maybe for minerals that we have not studied – like iodine – or because of its medicinal benefits. But we also found that gorillas often ventured into the cooler subalpine or alpine areas of the region, where they targeted plants known as land giants and lobelias. These have proved to be high in sodium too.

Human-wildlife conflict

The looting of crops is the main source of conflict between people living near the park and wildlife. Farmers generally perceive crop damage by mountain gorillas as an important deterrent to their agricultural development.

The risk is that encounters between gorillas and local people will exacerbate tensions and make local communities hostile to wildlife, impeding wildlife conservation efforts.

Close contact between gorillas and humans also increases the risk of disease transmission – such as respiratory diseases and intestinal parasites – which could have a detrimental impact on this extremely vulnerable apes population.

To discourage gorillas from entering agricultural lands near the forest, it may be necessary to modify agricultural practices, for example by using less plants than gorillas seek for their nutrients.

An ideal scenario would be to establish a buffer zone containing unattractive and unpalatable plants. If it were wide enough, it would deter gorillas from entering cultivated lands.

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