To test whether the call is used to recognize friends and strangers, researchers recorded the varying honks of seven different hippo groups living in Mozambique’s lake-filled Maputo Special Reserve and played them back to each group from a loudspeaker (above). The calls fell into one of three categories: from a hippo in the same clan, from a hippo living in the same lake (a “neighbor”), or from a stranger, either a hippo living in captivity or one residing several lakes over.
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When a group heard wheeze honks from a neighbor or from one of their own, they occasionally called back or lumbered in the direction of the call. But when the hippos heard an unfamiliar voice, they got aggressive. The giant mammals honked back, approached the speaker and were more likely to mark their territory, the team reports today in Current Biology, defecating and spraying feces in all directions by spinning their tails like propellers.
This kind of vocal recognition isn’t unique among large animals. Elephant seals remember the sounds and rhythms of their rivals’ voices, for example. But the new findings could help researchers better manage hippo populations, which are often relocated when threatened by hunting or habitat loss. The voices of incoming animals could be played for local hippos to acclimate them to their soon-to-be neighbors and decrease aggression, the researchers say.
