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.”
audible Something that can be heard, usually with ears or other sound-sensing structures.
audio Having to do with sound.
biology The study of living things. The scientists who study them are known as biologists.
calf (plural: calves) The name of young animals in a range of mammalian species, from cattle to walruses.
dolphins A highly intelligent group of marine mammals that belong to the toothed-whale family. Members of this group include orcas (killer whales), pilot whales and bottlenose dolphins.
journal (in science) A publication in which scientists share their research findings with experts (and sometimes even the public). Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.
killer whale A dolphin species (Orcinus orca) whose name means whale killer. These animals belong to the order of marine mammals known as Cetacea (or cetaceans).
orca The largest species of dolphin. The name of this black-and-white marine mammal, Orcinus orca, means killer whale.
predator (adjective: predatory) A creature that preys on other animals for most or all of its food.
prey (n.) Animal species eaten by others. (v.) To attack and eat another species.
range The full extent or distribution of something. For instance, a plant or animal’s range is the area over which it naturally exists. (in math or for measurements) The extent to which variation in values is possible. Also, the distance within which something can be reached or perceived.
repertoire A stock of regularly performed songs
sensor A device that picks up information on physical or chemical conditions — such as temperature, barometric pressure, salinity, humidity, pH, light intensity or radiation — and stores or broadcasts that information. Scientists and engineers often rely on sensors to inform them of conditions that may change over time or that exist far from where a researcher can measure them directly. steer A castrated male bovine raised for meat.
tone Changes in a voice that express a particular feeling or mood.
wave A disturbance or variation that travels through space and matter in a regular, oscillating fashion.
whale A common, but fairly imprecise, term for a class of large mammals that lives in the ocean. This group includes dolphins and porpoises.
Journal: M.L.K. Nielsen et al. Acoustic crypsis in southern right whale mother–calf pairs: infrequent, low-output calls to avoid predation? Journal of Experimental Biology. Published online July 11, 2019. doi: 10.1242/jeb.190728.