On the elephant trail

What if memory wasn't elephants' most astonishing attribute? Researchers theorize that the migratory routes taken by elephant herds each year may be determined by their exceptional sense of smell, enabling them to smell rain from a great distance.

Stephanie Periquet / CNRS Photothèque

"It's a smell typical of the ecological systems we live in. It's like the smell of wet earth after months of drought, on which violent storms suddenly erupt. At times like these, the smell is everywhere, very strong!" We're in southern Africa, on the border between Botswana and Zimbabwe. In Hwange National Park, Simon Chamaillé-Jammes, a researcher at the Centre d'écologie fonctionnelle et évolutive*, has been observing the 40,000 elephants that inhabit this protected area the size of Belgium, and not the rain, for almost 20 years.

Memory card

40,000 elephants are also concerned by the smell of this rain, which becomes vital when the great drought strikes, forcing the matriarchs and their herds to take to the road again year after year, in search of this precious water. A great migration always shrouded in the mystery in which it takes place: the memory of elephants. To document this phenomenon, researchers, in collaboration with the Zimbabwean National Parks Authority, have been fitting elephants with GPS collars for two or three years since 2009(Science direct - November 2017).

Thanks to this device, they were able to follow the migratory routes of these giants for the first time, sometimes tracing straight lines over 250 kilometers. They also discovered that certain groups of elephants did not migrate at all; but above all, they were able to confirm that "matriarchs reproduce the routes passed down to them by their mothers, while adjusting to current conditions when the usual watering holes dry up", thus probably enriching a memory that can be mobilized when a new drought occurs.

Migration on the fly

This observation confirms the existence of this legendary elephant memory, but does not rule out the possibility of another explanation: that of an elephantine sense of smell, capable of detecting rain from tens of kilometers away or even further. This characteristic wet earth smell is a cocktail of several molecules, including geosmin, which can be reproduced synthetically," explains the researcher. So we carried out experiments on tame elephants to see if they could smell and identify this molecule." And the answer was yes.

To complete the experiment and demonstrate that elephants can use this scent as a guide when on the move, the scientists plan to release this molecule into the environment of tame elephants to observe their reaction. Some researchers think they could track the smell of rain over 100 kilometers away," explains Simon Chamaillé-Jammes. What we already know for sure is that it's not just memory or perception that governs these migrations, but both. It remains to be seen what weight they give to one or the other.

Elephants without borders

Behind the ecological and scientific interest of these observations, another challenge is emerging, that of the conservation and management of these species which, in order to migrate, do not hesitate to cross the very artificial borders of states. "When an elephant migrates, it will be counted and managed by Zimbabwe, then a few months later it will be counted by Botswana, even though it's the same animal. This shows that conservation can in no way be thought of on a national scale," explains the ecologist.

To better manage these important elephant populations, a huge transnational conservation area called KAZA, including Hwange Park, has been created between Botswana, Zimbabwe, Angola, Namibia and Zambia. The aim? To centralize all data relating to these species in a single institution, so as to better guide conservation policies, notably by preserving the ecological corridors linking the protected areas. This is a priority if we are to ensure that elephants are no longer hindered on their age-old journey.