Dolphin moms use ‘baby talk’ with their calves | Science

Parents around the world coo at their babies in swooping, high-pitched tones called “motherese,” or baby talk. This exaggerated way of speaking—which we also use with our pets—is thought to help infants bond with their caregivers and learn the boundaries between syllables and words.

Dolphins, it turns out, may do the same. In a study published today in the Proceedings of the National Academy of Sciences, researchers report that bottlenose dolphin mothers heighten the pitch of their whistles when communicating with their calves. The behavior—the first time motherese has been found in a nonhuman animal—may enhance bonding and, possibly, learning.

The findings will lead to a boom in animal communication studies, predicts Janet Mann, a behavioral ecologist and bottlenose dolphin expert at Georgetown University who was not involved with the work. They may even provide insight into the evolution of vocal learning, she says, a prerequisite for language.

Every bottlenose dolphin has a “signature whistle” that functions like our names do. The animals use them to initiate and maintain contact with other dolphins and to communicate urgency. Dolphin calves acquire these high-pitched calls in their first year of life, though researchers aren’t sure how. Calves also learn the “names” of their mothers, friends, and pod mates and imitate them to get their attention or to call for assistance.

Scientists with Florida’s Sarasota Dolphin Research Program had been recording the whistles of adult female dolphins and their calves for decades in Sarasota Bay, building up a large database, when they got the idea to start looking for signs of motherese. For their work, the researchers herd known mother-calf pairs into shallow sea cages or slings and keep them close together. Calves stay with their mothers for 2 to 6 years; all the calves in the study were 2 years old. While assessing the animals’ health, the scientists also record their nonstop whistles through special devices they attach with suction cups to the dolphins’ forehead bumps, or “melons.”

“They are in acoustic contact 100% of the time,” says Laela Sayigh, a biologist at the Woods Hole Oceanographic Institution and the study’s lead author. “We have no idea of what they’re communicating, but likely, it’s, ‘I’m here. I’m here.’”

From the dolphin whistle database, the scientists selected a set of 19 females that had been recorded both with and without a calf between 1984 and 2018. For each individual dolphin, the researchers randomly selected 20 whistles to study. Spectrograms (visual representations of the sounds) showed the contour and bandwidth of every animal’s whistle.

All 19 mother dolphins produced higher frequency whistles when in the presence of their calves than when alone, the team found. They also emitted slightly lower minimum frequencies only when with their calves. These higher and lower frequency patterns produced an overall greater bandwidth—mirroring the patterns seen in human motherese, the researchers say.

Sayigh says she doubts the female dolphins’ whistles indicated stress because another study has shown that stressed females increase their whistle rate—something the mothers in this study did not do. “It was very much like what human mothers do when they talk in a high-pitched voice to their infants.” (Listen to a mother dolphin’s whistle with and without her calf below. The whistles have been slowed down to make the differences audible.)

Human babies are known to prefer motherese over adult speech. The dolphin researchers don’t yet know whether dolphin calves prefer motherese whistles. But for humans, this way of speaking seems to help children bond with their caretakers while learning the complex features and structure of language.

By age 2, dolphin calves have already established their own signature whistles, so their mothers likely weren’t teaching them how to produce their “names,” Sayigh says. Instead, she thinks the mothers use motherese to tell their calves to pay attention, and perhaps to better identify whistles directed specifically at them, while enhancing their bond.

Elise Piazza, a brain and cognition scientist and motherese researcher at the University of Rochester who was not involved with the work, agrees. “It makes sense that dolphins would use their version of motherese almost solely for bonding,” she says, given their large, mobile societies, and the necessity of staying in touch over sometimes long distances.

Even if dolphin and human motherese serve somewhat different purposes, the work could still have important implications for understanding the evolution of language in humans, says Karl Berg, a behavioral ecologist at the University of Texas Rio Grande Valley who was not involved with the study. Finding this kind of convergence—especially in such distantly related species as humans and dolphins—should help scientists seeking to understand the evolutionary origins of vocal learning, he says, a fundamental part of language.

The work may also inspire others to look for motherese in other vocal-learning species, such as parrots and seals. “Any vocal-learning species with substantial social bonds between parent and offspring might show this,” Berg says. Let the search begin.

Parents around the world coo at their babies in swooping, high-pitched tones called “motherese,” or baby talk. This exaggerated way of speaking—which we also use with our pets—is thought to help infants bond with their caregivers and learn the boundaries between syllables and words.

Dolphins, it turns out, may do the same. In a study published today in the Proceedings of the National Academy of Sciences, researchers report that bottlenose dolphin mothers heighten the pitch of their whistles when communicating with their calves. The behavior—the first time motherese has been found in a nonhuman animal—may enhance bonding and, possibly, learning.

The findings will lead to a boom in animal communication studies, predicts Janet Mann, a behavioral ecologist and bottlenose dolphin expert at Georgetown University who was not involved with the work. They may even provide insight into the evolution of vocal learning, she says, a prerequisite for language.

Every bottlenose dolphin has a “signature whistle” that functions like our names do. The animals use them to initiate and maintain contact with other dolphins and to communicate urgency. Dolphin calves acquire these high-pitched calls in their first year of life, though researchers aren’t sure how. Calves also learn the “names” of their mothers, friends, and pod mates and imitate them to get their attention or to call for assistance.

Scientists with Florida’s Sarasota Dolphin Research Program had been recording the whistles of adult female dolphins and their calves for decades in Sarasota Bay, building up a large database, when they got the idea to start looking for signs of motherese. For their work, the researchers herd known mother-calf pairs into shallow sea cages or slings and keep them close together. Calves stay with their mothers for 2 to 6 years; all the calves in the study were 2 years old. While assessing the animals’ health, the scientists also record their nonstop whistles through special devices they attach with suction cups to the dolphins’ forehead bumps, or “melons.”

“They are in acoustic contact 100% of the time,” says Laela Sayigh, a biologist at the Woods Hole Oceanographic Institution and the study’s lead author. “We have no idea of what they’re communicating, but likely, it’s, ‘I’m here. I’m here.’”

From the dolphin whistle database, the scientists selected a set of 19 females that had been recorded both with and without a calf between 1984 and 2018. For each individual dolphin, the researchers randomly selected 20 whistles to study. Spectrograms (visual representations of the sounds) showed the contour and bandwidth of every animal’s whistle.

All 19 mother dolphins produced higher frequency whistles when in the presence of their calves than when alone, the team found. They also emitted slightly lower minimum frequencies only when with their calves. These higher and lower frequency patterns produced an overall greater bandwidth—mirroring the patterns seen in human motherese, the researchers say.

Sayigh says she doubts the female dolphins’ whistles indicated stress because another study has shown that stressed females increase their whistle rate—something the mothers in this study did not do. “It was very much like what human mothers do when they talk in a high-pitched voice to their infants.” (Listen to a mother dolphin’s whistle with and without her calf below. The whistles have been slowed down to make the differences audible.)

Human babies are known to prefer motherese over adult speech. The dolphin researchers don’t yet know whether dolphin calves prefer motherese whistles. But for humans, this way of speaking seems to help children bond with their caretakers while learning the complex features and structure of language.

By age 2, dolphin calves have already established their own signature whistles, so their mothers likely weren’t teaching them how to produce their “names,” Sayigh says. Instead, she thinks the mothers use motherese to tell their calves to pay attention, and perhaps to better identify whistles directed specifically at them, while enhancing their bond.

Elise Piazza, a brain and cognition scientist and motherese researcher at the University of Rochester who was not involved with the work, agrees. “It makes sense that dolphins would use their version of motherese almost solely for bonding,” she says, given their large, mobile societies, and the necessity of staying in touch over sometimes long distances.

Even if dolphin and human motherese serve somewhat different purposes, the work could still have important implications for understanding the evolution of language in humans, says Karl Berg, a behavioral ecologist at the University of Texas Rio Grande Valley who was not involved with the study. Finding this kind of convergence—especially in such distantly related species as humans and dolphins—should help scientists seeking to understand the evolutionary origins of vocal learning, he says, a fundamental part of language.

The work may also inspire others to look for motherese in other vocal-learning species, such as parrots and seals. “Any vocal-learning species with substantial social bonds between parent and offspring might show this,” Berg says. Let the search begin.