February 1, 2023

Hippos Recognize Each Other’s Voices – And Respond Differently to Calls of Strangers

Their “wheeze honk” calls can be heard over long distances, leading researchers to believe the calls play a crucial function in keeping social groups. Now, a research study published in the journal Current Biology on January 24, 2022, shows that hippos acknowledge each others voices. When the hippos are in the water, they look quite inactive, Mathevon describes. When they heard the call of another hippo played from the shore, they responded right away. The findings use useful insights into hippo interaction and social groups.

Hippopotamuses are rather singing animals. Their “wheeze honk” calls can be heard over long ranges, leading scientists to think the calls play a crucial role in keeping social groups. Now, a study published in the journal Current Biology on January 24, 2022, shows that hippos recognize each others voices. They also react less aggressively to the calls of a next-door neighbor compared to those of a complete stranger.
” We found that the vocalizations of a complete stranger person induced a stronger behavioral action than those produced by individuals from either the very same or a neighboring group,” says Nicolas Mathevon of University of Saint-Etienne, France. “In addition to revealing that hippos are able to determine conspecifics based upon singing signatures, our research study highlights that hippo groups are territorial entities that act less aggressively toward their next-door neighbors than toward complete strangers.”


Listen to a hippos “wheeze honk” call. Credit: Nicolas Mathevon
When the hippos are in the water, they look quite inactive, Mathevon describes. When they heard the call of another hippo played from the shore, they reacted right away.
The findings use helpful insights into hippo interaction and social groups. They also have essential ramifications for conservation policy, the scientists state.
” Before relocating a group of hippos to a new area, one safety measure may be to transmit their voices from a loudspeaker to the groups currently present so that they become familiar with them and their aggressiveness gradually decreases,” Mathevon states. “Reciprocity, in which the animals to be moved ended up being familiar with the voices of their brand-new neighbors before they get here, could also be thought about.”
In future research studies, the scientists intend to find out more about what hippos interact through their calls. Theyll check out how they recognize the sound of other hippos and whether the voices hand out other attributes, such as sex, age, or size.
Referral: “Voice-mediated interactions in a megaherbivore” by Julie Thévenet, Nicolas Grimault, Paulo Fonseca and Nicolas Mathevon, 24 January 2022, Current Biology.DOI: 10.1016/ j.cub.2021.12.017.

The researchers discovered that hippos respond to hearing a played-back call by responding vocally, approaching, and/or spraying dung. Interestingly, the reaction differed depending on whether they were hearing hippos that they knew or ones they didnt.
The overall strength of the hippos response grew when they heard a stranger. The hippos were also more likely to spray dung, a territorial marking behavior, when they heard the noise of a hippo that didnt come from their group.

Hippopotamus with its mouth open. Credit: Nicolas Mathevon
Mathevon and his associates are interested in bioacoustics, the research study of how animals exchange details through noise. Theyre especially interested in interaction networks, in which several individuals receive and send out info at one time.
Hippos are tough animals to study due to the fact that it can be challenging to determine and locate people. The scientists managed it by working in the Maputo Special Reserve, Mozambique, an area that includes numerous lakes lived in by hippos.
First, Mathevon and his team recorded calls agent of each hippo group. Then, the researchers played the recordings back to all the other hippos to see how they d react to the calls of their own group (familiar) versus another group from the same lake (neighbor) or a more remote group (complete stranger).

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