At a glance, the life of a hippopotamus might look easy as they cruise sedately in water. But new research has shown that they are not just chilling but are actually listening for unfamiliar sounds. Any unwelcome bellow or grunt from a newcomer will see them flinging faeces at the intruder.
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Wheez Honks
In a study published in Current Biology, researchers observed hippos at the Maputo Special Reserve in Mozambique. A close study of the animals revealed that they recognize and respond differently to the calls of different hippos in the area.
Apart from spraying dung to mark their territory, hippos have also been found to act this way if an unfamiliar hippo enters their territory. The second author of the report, Nicolas Mathevon of the University of Saint-Étienne, France, said:
We found that the vocalisations of a stranger individual induced a stronger behavioural response than those produced by individuals from either the same or a neighbouring group.
Specifically, the hippos could differentiate a familiar hippo from a stranger by the sound of their 'wheeze honk—' the animals’ signature call. If the call was from a close river-mate, hippos tended to call back and wander towards the call, remaining relaxed.
Poop-Flinging Display
But upon hearing calls from strangers, hippos became agitated and aggressive, using their tails in whip-like fashion to spray dung in a territorial display. Mathevon explained:
In addition to showing that hippos are able to identify conspecifics based on vocal signatures, our study highlights that hippo groups are territorial entities that behave less aggressively toward their neighbours than toward strangers.
While the new study reveals how wheeze honks may help hippos define their social groups and distinguish friend from foe, researchers believe their findings could also have important implications for conservation policy. Mathevon added:
Before relocating a group of hippos to a new location, one precaution might be to broadcast their voices from a loudspeaker to the groups already present so that they become accustomed to them, so their aggression gradually decreases.
