This shows that the whales use an advanced form of acoustic communication, according to the Danish researcher Jonas Teilmann, professor at the University of Århus.
It's about hundreds of dives over a week that are synchronized. It's unlikely that it would be a coincidence that two individuals dive at the same second so many times, he says to the Danish news agency Ritzau.
The twelve whales that the researchers followed have all been equipped with some form of transmitter and then the researchers have used data loggers to track the whales' movement patterns.
What they have in common is that when they are within ten nautical miles of each other, they dive exactly at the same time, Teilmann explains.
We believe that the whales communicate about food resources, he says.
The Greenland whale belongs to the baleen whales. It is one of the world's largest mammals, can grow up to 18 meters long and weigh up to 100 tons.
