Hippo Calls Studied
A new study has revealed that hippos are able to tell the difference between vocal noises of hippos they are familiar with and those of strangers. The research has highlighted that they react differently according to whether they think the call is from a friend or foe.
Difficult to research
Hippos are one of the largest animals on the planet yet we know very little about their behaviour. They spend large amounts of their life in the water, only coming out at night to graze. They are also notoriously hostile to any intruders to their territory and can move fast through both water and on land.
To carry out the research the French and Portuguese team had to set up sound recording equipment at a suitable distance away from the hippos. Thankfully the hippos calls can be heard more than half a mile away so the team didn’t need to get too close.
Mozambique hippos studied
The team collected data from seven hippo groups in Mozambique’s Maputo Special Reserve. Once they had amassed a decent amount of recordings they then played the calls back to each group. First they would play them to hippos in the same group and then to a neighbouring group within the same lake, and finally they played them to a group from another lake.
When the recordings were played, the hippos more often than not reacted by making their own calls straight back and approached the area that the recording was coming from, so approaching the ‘speaker’. Sometimes the hippos would also react by spraying out poo and flinging it around using their tail. The hippos reacted much more strongly, spraying more poo, if the recorded calls were from a stranger from a different group.
Marking territory
The spraying of poo is thought to be a sign of marking their territory so it makes sense that they would choose that behaviour when hearing a call from a hippo that they were unfamiliar with. Essentially they are warding off rival hippos, but choose not to react that way if they are familiar with the call even if it is from a neighbouring group.
The research could be useful when hippos have to be moved for their own protection. In the future the calls from a new neighbouring group can be played to the moving group in advance so that they can get used to the new neighbours, and vice versa.
