The sight of chubby baby cheeks is often enough to transform even the most committed curmudgeon into a babbling softie.
Sentences become shorter, sounds are exaggerated, and the overall pattern of speech is more singsong and musical.
Researchers have dubbed this “motherese,” or, more formally, “infant-directed speech.”
“We’re not changing the words that we’re saying, we’re changing the way that we’re saying them,” says Laela Sayigh, a marine biologist at the Woods Hole Oceanographic Institution and Hampshire College in Massachusetts.
Only a handful of other species have been shown to change their calls when addressing young, including zebra finches, rhesus macaques, and squirrel monkeys.
Now, Sayigh’s new study, based on three decades of data in Florida, reveals common bottlenose dolphins use motherese — one of the first times it’s been documented in a species other than humans.
It's a major discovery, agrees Rindy Anderson, a behavioral ecologist at Florida Atlantic University who was not involved with the research.
The study, published today in the Proceedings of the National Academy of Sciences, "suggests that using these modifications when communicating with young assists them in learning how to produce these calls themselves,” she says.
Learning language is hard. Yet infants, incredibly, sop up the verbal soup around them and learn how to construct sentences with the appropriate structure.
How? The answer has to do with how we intuitively talk to babies.
Making our sentences shorter strips away unnecessary words. Emphasizing sounds makes words clearer. And — importantly — we increase the pitch of our speech.
Studies have shown these vocal characteristics grab and hold the attention of children far better than normal adult-directed speech.
And when parents are coached on how to use motherese, their child babbles more and has a bigger vocabulary as a toddler.
Language scientists make an important distinction between motherese and what is commonly referred to as baby talk.
The latter, they say, consists of largely made-up words with inconsistent and incorrect grammar and syntax:
It’s the difference between telling a baby, “Look at that DOGGY!” and “Wook at dat widdle puppy-wuppy!”
That’s why the list of species that use the more accurate motherese has so far been limited.
“Vocal learning is actually very rare. Out of the millions of species that use sound to communicate, there’s just a few groups that must learn their vocal communication systems,” Anderson says.
When Sayigh began working with a pod of wild bottlenose dolphins in Florida’s Sarasota Bay in the late 1980s, she observed that these marine mammals shared many characteristics with humans.
For instance, mothers and their offspring live within intricate social groups held together by a complex language of songs and whistles.
Over time, the biologist began to wonder whether females use motherese to communicate with their calves.
Bottlenose mothers nurse their young for two years, and the animals generally stay with her until they’re between three to six years old, learning how to hunt, navigate, and stay safe in the ocean.
Father dolphins generally aren’t involved in rearing their young.
Dolphin communication is profoundly different from how humans talk.
The most common dolphin vocalization is their signature whistle, a sound unique to each dolphin that serves as the cetacean equivalent of a “Hello, My Name is…” sticker.
Dolphins, however, don’t use another animal’s signature whistle to direct communication.
Instead, they repeat their own signature whistle and listen for another dolphin to respond with their own.
It’s analogous to your mother standing on your front porch and yelling her own name to summon her kids, says Kelly Jaakkola, a cognitive psychologist and marine mammal biologist at the nonprofit Dolphin Research Center in Grassy Key, Florida.
As part of their ongoing research, the Sarasota Dolphin Research Program performs regular veterinary exams on the wild dolphins, which have gotten used to the scientists’ presence.
During these exams, Sayigh and colleagues would sometimes attach a small recording device called a hydrophone to a mother dolphin’s forehead with a fist-size suction cup that the researchers later removed.
By analyzing recordings of 19 different female dolphins over 34 years, Sayigh found that the signature whistles of dolphin mothers had a greater range of frequencies — the high pitches were higher and the lows were lower — when their calves were nearby.
The high-pitched sounds are out of the range of human hearing.
To Jaakkola, who wasn’t part of the study, this work was “a fantastic first step.”
“The data here are beautiful,” she says. “The trick comes in possible interpretations of what’s happening.”
The work only looks at dolphin communication in one specific context, which means scientists can’t say definitively that the dolphins are speaking to their calves in motherese, Jaakkola says.
For instance, the results could be due to vocal changes in caused by lactation, or some other unknown variable.
However, in a 2017 study, researchers noticed an identical change in mother dolphins’ signature whistles while examining the effects of human-made noise, which lends support to the authors’ conclusions that the dolphins change their pitch as needed.
For Sayigh, the questions are endless — and fascinating.
“I just can't even articulate what an amazing project it is. I could spend three lifetimes there,” she says.
