Hippopotamuses are some of the most hostile animals.
Nicolas Mathevon, a professor of animal behavior at the University of Saint-Etienne in France, said that they are the most dangerous animal in Africa. People underestimate them. They swim fast and don't hesitate to attack boats. They are in the water most of the time, but they can leave the water very quickly. Entering their territory can be dangerous.
Hippos give adequate warnings to strangers.
The large mammals make loud noises, and Dr. Mathevon and his colleagues have worked out what they mean. Hippopotamuses can distinguish friends from acquaintances by the way they sound, according to their results published Monday.
Hippos are difficult to study. It is hard to find individual animals even when marked. They spend the night feeding on land, and then retreat to the water during the day, gathering in groups with a dominant male guarding a number of females and young animals. The details of a person's social organization are poorly understood.
Dr. Mathevon and his colleagues continued. They studied the animals at the Maputo Special Reserve, where there are many lakes with different groups of Hippos. The researchers recorded the calls of Hippos.
From at least 250 feet away, the researchers made their recordings using sophisticated video equipment and a shotgun microphone. They played the recordings back to the others.
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Hippos make a lot of noise. They can be heard more than a half-mile away, with their grunts, bellows and shrieks. The social function of the wheeze honk is not clear.
In 10 separate experiments, the scientists played recorded calls to the animals, first by playing a Hippo's voice to its own group, second by a neighboring group in the same lake and third by a stranger from another lake. They made videos of the responses.
Hippos respond to calls by calling back, approaching the caller or marking their territory by defecating while flicking their tails. When the animals heard recordings of people from their own group, the intensity of their response was the lowest, while when they heard a distant stranger, it was the highest. Territorial marking was caused by the call of an animal from a group of strangers, but the reaction to a call from a neighboring group was the same.
It is a image.
A hippo can be heard grunts, bellows and shrieks more than a half-mile away. Nicolas Mathevon was given a credit.
It can be hard to maintain objectivity in animal behavior studies. He said that there is always a danger to imagine things that don't exist. You have to take precautions in both the techniques for gathering data and the methods used to interpret it.
The researchers waited until the animals were calm. Five different people looked at the number of hippos. Researchers not involved in producing the videos scored the responses of the animals on three-point scales using three criteria: distance of approach toward the sound, degree of marking by dung spraying and number of hippos vocalizing.
The study could have implications for the preservation of the species. Hippopotamus populations are declining, and the International Union forConserving of Nature considers them vulnerable.
Diana Reiss, an animal behavior researcher and professor of psychology at Hunter College in New York who was not involved in the study, said that the finding that Hippos show stronger behavioral reactions to the calls of an unknown Hippo can be applied to the effort to save the Hippo. It may be beneficial to habituate Hippos that may need to be relocated to other areas for the sake of conservativism.
There is a lot to learn about group dynamics.
Hippos have a complicated social system. The vocal system has a lot of complexity. Hippos can distinguish between familiar and unfamiliar voices. The study is only the first step.
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