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Aggressive hippos far more tolerant to neighbours they know than strangers, reveals a new study

Considered dangerous than even grizzly bears, not much is known about hippos, especially their social communication

While hippopotamus look menacing and are reckoned to be far more threatening to humans than big grizzly bears, the world and science knows relatively less about the third largest mammal, especially their social communication.

A recent study brought to light some vital aspects of their individual and group behaviour as it has been found that they are not fond of strangers and shower poop when they hear the sound of strange hippos as per a study in sciencealert.com.

The details of the study were published in Current Biology.

Elaborating on the study and its findings, one of its authors Nicolas Mathevon, who is a bio-acoustician at University of Saint-Etienne said: “We found that the vocalizations of a stranger individual induced a stronger behavioural response than those produced by individuals from either the same or a neighbouring group. In addition to showing that hippos are able to identify [other hippos] based on vocal signatures, our study highlights that hippo groups are territorial entities that behave less aggressively toward their neighbours than toward strangers."

As part of their study the researchers went to Mozambique and started recording calls from seven hippo groups across three lakes in Maputo Special Reserve. Their focal point was the “wheeze honk”, which is one of the routine vocalisation of these animals. It is supposed to be a part of their social cohesion communications and is audible over long distances.

In their paper, the scientists wrote: "Studying the behavioural biology of hippos in the wild is complicated. It is difficult, if not impossible, to identify and mark individuals and sometimes highly challenging to locate them. Hippos feed on land mainly at night and are rather solitary.”

They went on to add: "During the day they gather in groups in the water. Hippo groups are socially structured around a dominant male, a variable number of females and their young, and some peripheral males. However, it is unclear whether individuals in a pod form a stable group defending a territory or pods are organised in a fission-fusion manner with individuals moving from one pod to another."

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Having taped the calls of the hippos, to find out the reaction of the creatures, the wheeze honk was played to them. The aim was to study their reaction to the sound emanating from the members of their group, from their neighbours who shared the lake with them and those which came from stranger hippos from another lake.

Looking at the reaction of the creatures, the scientists found that the responses in terms of behaviour like calling back or marking of territory was done by scattering of poop. The pertinent difference was that in the case of strangers, the level of pooping was high.

Talking about this, the team wrote: "Whereas individuals responded to calls from any group, marking behaviour (dung spraying) is modulated by the category of the calls. Stranger group calls induce more marking than calls from an individual of the same group, while there is no significant difference between reactions to the calls from the same group or from a neighbouring group."

What really makes this response amazing is that even though in water the hippos looked relaxed, yet they were alert to the sounds coming from their surroundings.

Also read: Older male elephants discipline adolescent males curbing their aggression – study

Also it indicated that they were more tolerant to their neighbours than to strangers which may not always hold true, as in some cases, hippos who are territorial may be far more aggressive to close-by fellow creatures than those from other places.

It also provides an important pointer when these creatures have to be relocated.

Mathevon observed: "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. Reciprocity, in which the animals to be moved become accustomed to the voices of their new neighbours before they arrive, could also be considered."