One of the most distinguishing sounds in animal kingdom is the hippo’s “wheeze honk”. A new study now shows how the animals can recognize the individual honks of their friends.
Researchers led from the Jean Monnet University studied the behaviour of groups of hippos living in a nature reserve in Mozambique.
Their findings suggest that the animals’ calls — which can be heard over great distances — help to maintain social groups, with strangers’ honks responded to more aggressively.
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Hippopotamuses can tell each other apart based on the ‘wheeze honk’ noises they make — responding differently to strangers than members of their own social group
The investigation was undertaken by bioacoustics expert Nicolas Mathevon of the Jean Monnet University in Saint-Étienne, France and his colleagues, who are interested in particular in how animals form communication networks.
Professor. Mathevon explained.
“Our study reveals that hippos can identify conspecifics using vocal signatures. It also shows that they behave more friendly toward neighbours than towards strangers.
The team studied hippos in the Maputo Special Reserve in Mozambique, which contains several lakes inhabited by various groups of hippopotamuses.
Mathevon, Professor and colleagues started their research by taking representative calls from the various hippo groups within the reserve.
Next, they played these back to all the hippos in order to see how they would react to calls from their own group versus neighbouring groups that lived in the same lake and more and distant groups that lived on other lakes.
Researchers discovered that hippopotamuses respond to the playback of recorded sounds in many ways. They can either vocalize back or approach the source of sound.
The nature of their reaction seemed to be dependent on whether they were listening to recorded conversations of strangers or hippos.
The hippos were particularly sensitive to the sounds of strangers and more inclined to spray their territory with dung.
Professor Mathevon observed that hippos look “pretty inactive” when they are swimming in the water, as pictured. The team’s findings show that hippos are paying attention to their environment, according to Professor Mathevon.
The study will help scientists understand the communication patterns of hippos and may also have implications for conservation policies.
In particular, Professor Mathevon said, the relocation of hippos — an act often performed to help maintain local populations at healthy sizes — might benefit from additional precautions to help the animals better adjust.
He stated that one way to prevent a hippos group from being relocated to a different location is to transmit their voices to other groups so they get used to it and then their aggression decreases.
It could also include a method called “Reciprocity,” in which animals are made to hear the voices and movements of their neighbours prior to arriving.
The team has completed their first study and are looking into how hippos communicate with each other through their calls. This includes whether their voices can be used to identify different peers or if they have clues about age, sexual orientation, and so forth.
All findings were published in Current Biology.
The Maputo Special Reserve in Mozambique was the location of this study. This reserve contains several lakes that have been inhabited for different groups.