Do you know how hippos recognize each other? The question may make you smile, but it has been the subject of an in-depth study, carried out in the Maputo Special Reserve in Mozambique. The results of this survey, in which CNRS researchers and scientists from the University of Saint-Etienne participated, could well contribute to preserving the species. Explanations.
Published Monday in the journal Current Biology, the study reveals that hippos use voice recognition to “manage relationships between territorial groups”. In other words, they are able to identify their congeners or sense the presence of unknown hippos thanks to the different cries they can emit.
Excreta as a defense weapon
The researchers studied three groups: the “family”, i.e. hippos from the same herd, the “neighbors”, those who live on the same territory or around the same lake, and the “strangers”, those who do not know each other. not. In order to understand how their exchanges work, the scientists reproduced the different noises emitted by the pachyderms as well as possible by “rebroadcasting the cries on loudspeakers”. “This allows us to ask the animals questions,” explains Nicolas Mathevon, bioacoustician at the University of Saint-Etienne.
Result: the behavior of hippos differs from one cry to another. And when they sense an alien presence? “We see that they are not happy. They have a fairly aggressive reaction, replies the scientist. The hippopotamus then comes out of the water, walks towards the loudspeaker and it spills its excrement. This is his way of marking and protecting his territory. »
Get them used to the voice of newcomers
What relationship, you will tell us, with the preservation of the species? Most hippos live in environments hostile to their development because of the presence of man and because of the disappearance of their habitats. Hence the need to move them to find a more serene environment. Which is relatively complex. As you would have understood, a herd of pachyderms is much less easily moved than sheep. Especially when they find themselves face to face with “foreign” congeners.
The recommended solution, thanks to the results of this study, would be “to accustom the hippopotamuses to the voice of new arrivals, before being able to move them”, develops Nicolas Mathevon. And to conclude: “I don’t know if it would work because the voice is not the only criterion. But one could imagine that on a lake, where one would like to bring back another group of hippopotamuses, one could set up systems for broadcasting cries. So that these large herbivores acclimatize as well as possible to their new environment and agree to stay there.