Hippos are one of the most unfriendly creatures in the animal kingdom.
“Apart from mosquitoes, they are the most dangerous animal in Africa, the one that kills the most people,” said Nicolas Mathevon, professor of animal behavior at the University of Saint-Etienne in France. “People underestimate them. They swim very fast and do not hesitate to attack boats. They are in the water most of the time, but they can move out of the water very quickly. Entering their territory can be quite dangerous.”
But you can’t say that hippos don’t give a complete warning to strangers.
Large mammals make loud noises, and Dr. Mathevon and his colleagues figured out some of their meanings. Their results, published Monday in the journal Current Biologysuggests that hippos can distinguish friends from acquaintances and acquaintances from strangers by the way they make sounds.
Hippos are difficult to learn. It is almost impossible to identify and mark each animal, and it is difficult to find them even when marked. They feed at night on land, and then retreat into the water during the day, gathering in groups with a dominant male guarding several females and young animals. Individuals can move from one group to another – the details of their social organization are not well understood.
But Dr. Mathevon and colleagues persisted. They studied the animals at Maputo Special Reserve in Mozambique, where several lakes are home to one or more groups, or shells, of hippos. There, the researchers recorded hippo calls in seven shells.
The researchers made their recordings judiciously, from at least 250 feet away, using sophisticated video equipment and a shotgun microphone designed to capture audio from a distance. They then played back the recordings to others while videotaping their answers.
They found that hippos make a lot of noise. Their “wheezing whistles” can be heard more than half a mile away, and their verbal repertoire includes grunts, whistles, and squeals. The wheezing whistle is often thought of as hippos’ way of announcing their presence, but its social function is unclear.
In 10 separate experiments, the scientists played recorded calls to the animals using three tests: first by playing the hippo’s voice to its group, the second using a call from a group of neighbors. in the same lake and finally by the sound of a stranger from another group. Lake. They made videos of all the answers.
Hippos respond to calls by calling back, approaching the caller, or marking their territory by defecating while wagging their tails to disperse excrement. The animals responded in some way to recorded calls from any group, but the intensity of the response was lowest when they heard recordings of individuals from their shells and highest. when they hear a stranger’s whistle in the distance. The response to a call from a neighboring group was slightly different from that of a group of the same group, and hearing only the call of an animal from a group of strangers provoked territorial marking.
In studies of animal behavior, it can be difficult to maintain objectivity, Dr. Mathevon said. “There is always a danger in imagining things that do not exist,” he said. “So you have to take some precautions,” in both the data collection techniques and the methods used to interpret that data.
Before each recording, the researchers waited until the animals were calm and quiet. Five different observers assessed the hippopotamus population and compared their numbers. Researchers who were not involved in the video’s production scored the animals’ responses on a three-point scale based on three criteria: proximity to sound, level of fecal markings, and number of hippopotamus calls.
The study could have implications for the conservation of this species. Hippo populations are in decline and the International Union for Conservation of Nature classifies them as vulnerable.
“It was found that hippos showed stronger behavioral responses,” said Diana Reiss, an animal behavior researcher and professor of psychology at Hunter University in New York who was not involved in the study. with the call of an unknown hippo could be applied to conservation efforts. “Settling hippos that may need to be relocated to other areas for conservation purposes can be both important and beneficial, following the call of the alien hippos they will encounter in other locations. new point.”
The study highlights that there is much to learn about hippos behavior and group dynamics.
Dr Mathevon said: “Hippos have a complex social system, with many different interactions. “That often comes with complexity in the vocal system. We show that hippos can distinguish familiar and unfamiliar voices. But our research is just the first step.”
https://www.nytimes.com/2022/01/24/science/hippos.html For Hippos, a chime and a whistle mean more than just ‘Hello!’ [Video]