Whales migrate from ocean to ocean
Surprise in the ocean : Humpback whales overhear other species
Good ears are an advantage in the sea: the daylight disappears quickly with the depth, but deep tones in particular spread over long distances, sometimes hundreds of kilometers. Many sea creatures are adapted to this with excellent hearing. It helps them to get prey, not to become prey themselves and in partner search.
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Humpback whales off the coast of Norway and Svalbard seem to be among the particularly good listeners. As it now turns out, they can to some extent understand even other species of whales: they are able to distinguish orcas calls by their dialects - a very useful skill.
Because the dialects tell them whether the killer whales, which can be up to nine meters long, are dangerous for them or whether they could show them the way to good prey. Benjamin Benti from the University of St. Andrews, Scotland, and other researchers from France and Norway are now reporting this in the journal "Marine Ecology Progress Series".
Difficult to observe underwater
They actually have a major handicap in their research: whales have to come to the surface of the water to breathe, but spend most of their time underwater, where they are more difficult to observe.
Humpback whales are also hikers. In summer, with the help of many horn plates in their mouths, they sift crabs and small fish out of the water off the coast of Svalbard and Bear Island. Then they migrate south and in late autumn and winter eat their way on the coast of Norway with herring bacon.
They then move further south into warmer waters. There they give birth to their offspring and mate to maintain their population.
Then it's back to the north. Benti's team was already waiting there in early summer on Spitzbergen. The researchers attached suction cups to the skin of individual humpback whales. Underwater microphones, accelerometers and mini-transmitters were attached to these.
According to the team, the whales initially reacted to the attachment of the devices by flinching and partial diving. But soon they seemed to ignore the appendage.
During the actual experiments, the team played the calls of two orca populations to the animals from a distance. One of them is at home off the northwest coast of North America and hunts seals and other whales there. As adult humpback whales are up to 15 meters long and significantly larger than orcas, killer whales usually attack newborns or young animals.
Orcas communicate in different dialects
The orcas communicate with each other with a series of sounds. However, as the Canadian marine biologist John Ford found out in 1990, they communicate in different dialects depending on the population.
Benti's team played the calls of the orcas from the Canadian Pacific coast to the humpback whales off Svalbard. The big whales seemed to know that their offspring in the open sea in particular are in danger from these orcas. In seven out of eight experiments, the animals tried to swim away from the loudspeakers with the killer whale calls.
The humpback whales fled a few minutes after the researchers turned off their speakers for the killer whale calls. This is an indication that they even know details of the behavior of the orcas: Although they talk eagerly after a successful hunt, they remain silent during the hunt so as not to warn their prey in advance. If the researchers' loudspeakers fell silent, the humpback whales had reason to believe that the orcas had started to hunt.
Off the coast of Norway, on the other hand, the other killer whale population hunts herring with a sophisticated method: because a school of these fish split up quickly as soon as an killer whale approaches, its attack would come to nothing. Therefore, the orcas initially drive schools of herring to the surface.
The fish are then encircled with air bubbles. Sometimes the orcas circle their prey in ever tighter circles and turn their sparkling white bellies towards them. The herrings do not break out and the orcas draw their circles closer until a strong blow with the tail fin kills or stuns a number of fish, which the successful hunter then only has to pick up.
Humpback whales take their bearings from other species
These killer whales do not hunt humpback whales. The humpback whales know that too. When the researchers played calls from herring-hunter orcas off the island of Vengsøya off the coast of northern Norway in January, they hurried towards the loudspeaker signal in anticipation of a swarm of herring.
Obviously, the humpback whales are eavesdropping on other species, distinguish dialects and adjust their own behavior accordingly - and even very differentiated: When the researchers played the sounds of the seal hunters to them in the fjords near Vengsøya in winter, the humpback whales seemed to flee less often. Then the defensive adult humpback whales are well nourished and can take on the orcas more easily, suspect Benti and his colleagues.
They also find hiding places more easily in the fjords. This is exactly what has been observed in humpback whales off the Canadian Pacific coast: They hide from the killer whales in dense brown algae forests.
Listening to other species therefore offers humpback whales an important survival advantage - as long as they not only hear well, but also draw the right conclusions.
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