Science

Hippos spew 'tornado poo' when they hear the voice of a hippo stranger

It might sound gross, but this knowledge could help with hippo conservation efforts.

Hippos have an awareness of the sound made by neighbors and strangers.
Nicolas Mathevon

When you hear a stranger's voice, hopefully you don't react by releasing "tornado poo." Scientists have learned that hippopotamuses, however, have a tendency to defecate intensely upon hearing an unfamiliar hippo's call. That might sound melodramatic, but it's actually a way hippos mark their space. They're known to be aggressive and males sometimes in engage in battle.

A study published in the journal Current Biology on Monday delves into the secret social lives of hippos. News portal Science Media Exchange, which published the Cell Press release on the study, seems to be the one that came up with the evocative "tornado poo" description. That phrase doesn't appear in the paper, which prefers "dung spraying."

The research took place in the Maputo Special Reserve in Mozambique. The reserve is home to multiple groups of hippos residing in different lakes, giving researchers the chance to record calls (hippos sound a loud "wheeze honk") from animals that lived near each other, and from ones that were total strangers.

The researchers played the calls for the animals and monitored the reactions. "We found that the vocalizations of a stranger individual induced a stronger behavioral response than those produced by individuals from either the same or a neighboring group," said co-author Nicolas Mathevon of University of Saint-Etienne, France. Hippos responded to the recordings by vocalizing back, approaching or spraying dung, or sometimes a combination of those behaviors. The hippos were more likely to unleash dung when hearing a stranger's call. 

The study could help when hippos need to be moved as part of efforts to conserve the species. "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 and their aggression gradually decreases," Mathevon suggests. The same could be done for the hippos being moved, essentially a get-to-know-you effort on both sides.

Hippos are listed as vulnerable on the IUCN Red List of Threatened Species, which catalogs the conservation status of animals and plants. The researchers hope to learn more about how hippos communicate through future studies. They're expressive animals, whether they're using their mouths or a very different part of their anatomy.