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It has been said that language is what separates humanity from the rest of the animals, but increasingly we’re learning that’s not strictly true. Many animals use various calls to signify danger, a ready food source, or willingness to mate. Some animals also communicate in ways which say, “I know you’re there and I don’t like it.”
Hippos are one of the largest animals in Africa and are often considered slow and lumbering, almost dull creatures. But that couldn’t be further from the truth. For one thing, hippos are more likely to kill a person than any other animal on the continent, aside from mosquitos. But they have a more contemplative side as well. Hippos use a variety of vocalizations to communicate with their peers and with nearby bloats — bloat being the insulting yet hilarious name for a group of hippos.
Paulo Fonseca from the Department of Animal Biology at the University of Lisbon, and colleagues, went to Africa armed with vocal recordings, video cameras, and shotgun microphones in the hopes of better understanding the nuances of hippo vocalizations. Their findings were published in the journal Current Biology.
“We played back one kind of vocalization known as a wheeze honk,” Fonseca told SYFY WIRE. “We’d wait until they produced the sound to record it and then play it back. We also played back vocalizations from other groups either in the same lake or a different lake.”
The team of five scientists then observed and recorded the hippos to gather and analyze their responses. They looked for a few key indicators. Those included the amount of time it took for the targeted hippos to respond, how many vocal responses occurred, and what level of aggression was present, if any.
They found that when hippos are presented with vocalizations from within their own group, the response is comparatively mild. The hippos might orient their heads toward the source of the sound. Responses level up when they are exposed to vocalizations from another group in the same lake or river. They level up further still when presented with vocalizations of total strangers. Those responses range from dominant individuals walking or swimming toward the source of the sound to actions which are much more aggressive.
“You have different levels of territorial display and aggression. Among the most aggressive is marking,” Fonseca said. “They have a very small tail, and they wave it while pooing and you have a spray. This is a normal territorial behavior.”
It might sound funny, but it absolutely isn’t if you’re a hippo or other animal — humans included — in the area. The highest level of aggressive display involves widely opening the mouth and baring their teeth. Sometimes, hippos will mark and open their mouths at the same time. If you see them do that, run. It’s the last warning.
“We had one hippo who came out of the water and displayed laterally, marking everything and opening the mouth. We stopped our experiment, otherwise he probably would have attacked,” Fonseca said.
In addition to physical responses, scientists noted a difference in the number of individuals who would respond vocally depending on if the playback came from their group or one they didn’t recognize. They also found that the responses were highly predictable, to the point that they could eventually tell if hippos were responding to friends or foes based solely on their behavior.
Moreover, the study revealed a high likelihood that hippos not only recognize their own group as a whole, but that they recognize the voices of individuals.
“We can’t say with total certainty because we tested vocalizations from groups, but it’s very likely that they really have an understanding of individuals,” Fonseca said.
The study has important implications about population management outside of the purely scientific interest. Hippos sometimes need to be relocated and introduced into existing populations which are strange to them in order to maintain genetic diversity and the health of the species. The team suggests these scenarios might benefit from acclimating the relocated individual and the existing population to one another’s vocalizations in order to reduce the likelihood of violent response.
Not unlike people, hippos don’t like getting calls from individuals they don’t recognize. You know, we don’t blame them.