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Hippopotamuses are a number of the most unfriendly creatures within the animal kingdom.
“Other than mosquitoes, they’re essentially the most harmful animal in Africa, those that kill the most individuals,” mentioned Nicolas Mathevon, a professor of animal conduct on the College of Saint-Etienne in France. “Individuals underestimate them. They swim very quick and don’t hesitate to assault boats. They’re within the water more often than not, however they will transfer out of the water very quick. Coming into their territory may be fairly harmful.”
However you may’t say that hippos don’t give ample warnings to strangers.
The big mammals make loud noises, and Dr. Mathevon and his colleagues have labored out a few of what they imply. Their outcomes, revealed Monday in Present Biology, recommend that hippopotamuses can distinguish pals from acquaintances, and acquaintances from strangers, by the best way they sound.
Hippos are arduous to check. It’s virtually unattainable to determine and mark particular person animals, and tough to search out them even when marked. They spend the evening feeding on land, after which retreat to the water in the course of the day, gathering in teams with a dominant male guarding quite a few females and younger animals. People could transfer from one pod to a different — the small print of their social group are poorly understood.
However Dr. Mathevon and colleagues persevered. They studied the animals on the Maputo Particular Reserve in Mozambique, the place a number of lakes are inhabited by a number of teams, or pods, of hippos. There, the researchers recorded the calls of hippos in seven pods.
The researchers made their recordings cautiously, from not less than 250 ft away, utilizing subtle video gear and a shotgun microphone designed to select up distant sounds. Then they performed recordings again to the others whereas videotaping their responses.
They discovered that hippos make a variety of noise. Their “wheeze honks” may be heard greater than a half-mile away, and their verbal repertoire contains grunts, bellows and squeals. The wheeze honk is mostly thought of the best way hippos announce their presence, however its social operate is unclear.
In 10 separate experiments, the scientists performed recorded calls to the animals utilizing three exams: first by enjoying a hippo’s voice to its personal group, second utilizing a name from a neighboring group in the identical lake and at last with the sound of a stranger from one other lake. They made movies of all of the responses.
Hippos reply to calls by calling again, approaching the caller or marking their territory by defecating whereas flicking their tails to unfold the feces. The animals responded in a roundabout way to recorded calls from any group, however the depth of the response was lowest after they heard recordings of people from their very own pod and highest after they heard the honk of a distant stranger. The response to a name from a neighboring group was little totally different from that of 1 from the identical group, and solely listening to the decision of an animal from a pod of strangers provoked territorial marking.
In animal conduct research, it may be tough to keep up objectivity, Dr. Mathevon mentioned. “There’s at all times a hazard to think about issues that don’t exist,” he mentioned. “So you must take some precautions,” in each the strategies for gathering knowledge and the strategies used to interpret it.
Earlier than every recording, the researchers waited till the animals had been calm and quiet. 5 totally different observers made assessments of the variety of hippos, and in contrast their counts. Researchers not concerned in producing the movies scored the responses of the animals on three-point scales utilizing three standards: distance of strategy towards the sound, diploma of marking by dung spraying and variety of hippos vocalizing.
The examine could have implications for the preservation of the species. Hippopotamus populations are declining, and the Worldwide Union for Conservation of Nature classifies them as susceptible.
“The discovering that hippos present stronger behavioral reactions to the calls of an unknown hippo may be utilized to conservation efforts,” mentioned Diana Reiss, an animal conduct researcher and professor of psychology at Hunter Faculty in New York who was not concerned within the examine. “It could be necessary and helpful to habituate hippos that will have to be relocated to different areas for conservation functions, to the calls of unfamiliar hippos they are going to be encountering in new areas.”
The examine highlights that there’s a lot to study hippo conduct and group dynamics.
“Hippos have a social system that’s difficult, with varied interactions,” Dr. Mathevon mentioned. “That often goes together with complexity within the vocal system. We present that hippos can distinguish acquainted and unfamiliar voices. However our examine is just a primary step.”
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