Bottlenose dolphin moms use baby talk with their calves

When speaking to young kids, humans often use squeaky, high-pitched baby talk. It turns out that some dolphins do, too.

Bottlenose dolphin moms modify their individually distinctive whistles when their babies are nearby, researchers report June 26 in the Proceedings of the National Academy of Sciences. This “parentese” might enhance attention, bonding and vocal learning in calves, as it seems to do in humans.

During the first few months of life, each common bottlenose dolphin (Tursiops truncatus) develops a unique tune, or signature whistle, akin to a name (SN: 7/22/13). The dolphins shout out their own “names” in the water “likely as a way to keep track of each other,” says marine biologist Laela Sayigh of the Woods Hole Oceanographic Institution in Massachusetts.

But dolphin moms seem to tweak that tune in the presence of their calves, which tend to stick by mom’s side for three to six years. It’s a change that Sayigh first noticed in a 2009 study published by her student. But “it was just one little piece of this much larger study,” she says.

To follow up on that observation, Sayigh and colleagues analyzed signature whistles from 19 female dolphins both with and without their babies close by. Audio recordings were captured from a wild population that lives near Sarasota Bay, Fla., during catch-and-release health assessments that occurred from 1984 to 2018.

The researchers examined 40 instances of each dolphin’s signature whistle, verified by the unique way each vocalization’s frequencies change over time. Half of each dolphin’s whistles were voiced in the presence of her baby. When youngsters were around, the moms’ whistles contained, on average, a higher maximum and slightly lower minimum pitch compared with those uttered in the absence of calves, contributing to an overall widened pitch range.

These whistle adjustments echo baby talk because human caregivers use real words and language, just with certain inflections, Sayigh says. Formally called child-directed communication, these inflections typically involve higher pitches and a wider pitch range, like what was observed in the dolphins.

“Bottlenose dolphins are a prime candidate for child-directed or calf-directed communication,” says Quincy Gibson, a marine mammal behavioral ecologist who was not involved with the study. Similar to humans, these dolphins form strong mother-baby bonds and learn vocalizations.

But to confirm this study’s results, scientists should analyze signature whistles of freely swimming, unrestrained dolphin moms, notes Gibson, director of the University of North Florida Dolphin Research Program in Jacksonville. “We do need to look at this question in more natural and undisturbed conditions.”

And although researchers speculate dolphin parentese could have the same functions as in human speech, no one can be certain “until the day we can ask the dolphins what they’re actually doing,” says behavioral ecologist Mauricio Cantor of the Oregon State University Marine Mammal Institute in Newport, who was also not involved with the study.

Still, Sayigh says, “the idea that there might be similar forces driving [parentese] in such different species is just really cool.”