Whales are known for belting out sounds in the deep. But some may also whisper — to safeguard their young.
Orcas, better known as killer whales, are predatory dolphins. They can hunt in packs and take down big prey — such as baby right whales. Some southern right whale moms steer their calves to shallow waters. There, their newborns are less likely to be picked off by orcas.
The crashing of coastal waves may also mask the occasional quiet calls that the mother and calf make. This may help the whales stick together without broadcasting their presence to predators. That’s the finding of a new study. Researchers described the findings July 11 in the Journal of Experimental Biology.
Most whale calls are meant to be long-range. However, notes Mia Nielsen, “This shows us that whales have a sort of intimate communication as well,” she says. “It’s only meant for the whale right next to you.” Nielsen is a behavioral biologist who works at Aarhus University in Denmark.
She was part of a team that tagged nine female whales with audio recorders. They also carried sensors to measure motion and water pressure. When the whales were submerged below the noisy waves, the scientists could pick up the hushed calls. These “whispers” were soft enough to fade into the background noise by around a distance of 200 meters (650 feet) away.
An orca “would have to get quite close in the big ocean to be able to detect them,” says biologist Peter Tyack. He works at the University of St. Andrews in Scotland and was not involved with the study. He does, however, work with one of the new study’s authors on other projects.
The whispers showed up when the whales were moving, rather than when mothers were stationary and possibly suckling their calves. Using hushed tones could make it harder for the pair to reunite if separated. But the observed whales studied here tended to stay close to one another — about one body length apart.
Eavesdropping biologists have generally focused on the loud noises that animals make, notes Tyack. Studies such as this one, he says, suggest “there may be a repertoire among the calls of lots of animals that are specifically designed only to be audible to a partner who’s close by.”