Hippos recognize each other's voices, respond differently to calls of strangers

Date:
January 24, 2022
Source:
Cell Press
Summary:
Hippopotamuses are rather vocal animals. Their 'wheeze honk' calls
can be heard over long distances, leading researchers to suspect
the calls play an important role in maintaining social groups. Now,
a new study shows that hippos recognize each other's voices. They
also respond less aggressively to the calls of a neighbor compared
to those of a stranger.



FULL STORY ========================================================================== Hippopotamuses are rather vocal animals. Their "wheeze honk" calls can
be heard over long distances, leading researchers to suspect the calls
play an important role in maintaining social groups. Now, a study in
the journal Current Biology on January 24 shows that hippos recognize
each other's voices. They also respond less aggressively to the calls
of a neighbor compared to those of a stranger.


==========================================================================
"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," says Nicolas Mathevon (@MathevonNicolas) of University of Saint-Etienne, France. "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 neighbors than toward strangers." Mathevon and his colleagues are interested in bioacoustics,
the study of how animals exchange information through sound. They're
especially interested in communication networks, in which multiple
individuals send and receive information all at once.

Hippos are tough animals to study because it can be difficult to identify
and locate individuals. The researchers managed it by working in the
Maputo Special Reserve, Mozambique, an area that includes several lakes inhabited by hippos.

First, Mathevon and his team recorded calls representative 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 distant group
(stranger).

The researchers found that hippos respond to hearing a played-back call
by responding vocally, approaching, and/or spraying dung. Interestingly,
the response varied depending on whether they were hearing hippos that
they knew or ones they didn't.

The overall intensity 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 sound of a hippo that didn't belong to
their group.

When the hippos are in the water, they look pretty inactive, Mathevon
explains.

But these results show that they really are paying close attention to
their surroundings. When they heard the call of another hippo played from
the shore, they responded right away. "The responses to the sound signals
we broadcast were very clear, and we did not expect that," he says.

The findings offer useful insights into hippo communication and social
groups.

They also have important implications for conservation policy, the
researchers say. For instance, they explain, animals often are relocated
to maintain local populations at healthy sizes. But the findings suggest
that precautions are needed before making that kind of move.

"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 says. "Reciprocity, in which
the animals to be moved become accustomed to the voices of their new
neighbors before they arrive, could also be considered." In future
studies, the researchers hope to learn more about what hippos communicate through their calls. They'll explore how they recognize the sound of
other hippos and whether the voices give away other characteristics,
such as size, sex, or age.

========================================================================== Story Source: Materials provided by Cell_Press. Note: Content may be
edited for style and length.


========================================================================== Journal Reference:
1. Julie The'venet, Nicolas Grimault, Paulo Fonseca, Nicolas Mathevon.

Voice-mediated interactions in a megaherbivore. Current Biology,
2022; 32 (2): R70 DOI: 10.1016/j.cub.2021.12.017 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220124114834.htm

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