On the trail of the secrets of whale songs: When blue whales sing more during the day, they start their journey from their feeding grounds to their winter quarters, researchers have found. The animals may even coordinate with each other by shifting their singing activity so that they can set off together. A targeted recording of the signal in underwater recordings could serve to protect the sea giants from collisions with ships, say the scientists.
With a weight of up to 200 tons, it trumps even the largest dinosaurs – the blue whale (Balaenoptera musculus) is considered the heaviest animal of all time. But not only the gigantic dimensions of the marine mammals are fascinating. Scientists have long explored the amazing features and strategies on which the record giants’ way of life is based. In the current case, the focus was on the migration behavior and the vocalizations of the blue whales.
Like other representatives of the baleen whales, they are long-distance travelers of the seas: In summer the blue whales eat their fill in their food grounds in cold sea regions. With the sieve-like beards in their gigantic mouths, they filter tons of crabs out of the water and put on bacon. They then need it as a supply for their journey and the stay in the winter quarters of the temperate latitudes, where they mate and give birth to their offspring. The right timing is important when it comes to migration behavior, because the giants have less buffer capacity than one might think: it is important for their survival to appear at the respective location at the most favorable times possible in order to ensure optimal food intake and reproduction.
Listening to blue whales
Up until now, the song of the animals has primarily been assigned a role in communication with one another, which is related to reproduction. But other functions of the calls, which can be heard from afar under water, also appear conceivable. In order to uncover possible connections with migration behavior, the researchers led by William Oestreich from Stanford University listened carefully to animals in a blue whale population in the Eastern Pacific. Their feeding grounds are off the west coast of North America. After feasting in summer, they swim to the Pacific coast of Central America to reproduce there in winter. To investigate the associated singing behavior, the marine biologists evaluated recordings from underwater microphones in Monterey Bay over a period of five years. Measuring devices that they attached to 15 whales also provided crucial records.
“We found that the whales sing mainly at night during their summer stay – but when it becomes apparent that they are going on a journey, this pattern is reversed: They make sounds mostly during the day,” reports Oestreich. Specifically, the images of an animal showed, for example: During the feeding period, the whale raised its voice an average of thirteen times an hour at night – but only three times a day. When it became apparent in the data from the measuring instruments that he was stopping eating and moving south, the singing activity shifted: at night the whale only made sounds an average of five times an hour – compared to ten times during the day. As the researchers explain, for the first time they were able to clearly link changes in singing that had already been identified with migration behavior. “We see an acoustic signature of the new beginning in these shifts in the temporal pattern,” says Oestreich.
Signal for a collective departure?
The study expands a previously possibly one-sided view: “The meaning of whale songs is typically considered in the context of mating and reproductive behavior,” says Oestreich. “We are not denying this role, but it is interesting to note that there may be other functions of singing,” says the scientist. The exact meaning of the changed singing behavior is still unclear, but Oestreich now wants to pursue an interesting possibility. He suspects that it could serve to coordinate the animals with one another. The whales may stop searching for food and set off when they hear that the population is in a spirit of optimism. “It seems possible that the widely dispersed individuals convey such information through the characteristics of their singing behavior,” said Oestreich.
In addition to the importance for biology, the acoustic indications of the migration behavior of the blue whales could also serve to protect them, say the scientists. More precise information about the start of the migration could put ships on increased alert. Because since the whaling was stopped, the collision with large ships has been the greatest danger for the marine mammals, which are still threatened. “A lot of people are interested in our results in an applied sense – they want to use them for the management of marine habitats and to reduce the risks of collisions on shipping routes,” says Oestreich. We can’t expect miracles, but we can think about how the results could help protect the whales, ”says the researcher.
Source: Stanford University, technical article: Current Biology, doi: 10.1016 / j.cub.2020.08.105