Dolphins Use Baby Talk

"Motherese" is a term for a simplified and repetitive type of speech with exaggerated intonation and rhythm, often used by adults when speaking to babies.  The reason people use this "infant-directed speech," commonly called "baby talk," is not known, but some scientists believe it may help children learn to pronounce novel sounds.  Research dating back to the 1980s suggests that human infants may pay more attention to speech with a greater pitch range, as well as enhance attention and bonding.  While motherese is nearly universal across all cultures and languages when human adults interact with children, evidence among nonhuman species is very sparse.  Only a handful of other species have been shown to change their calls when addressing their young, including zebra finches, rhesus macaques, and squirrel monkeys.  But none of these used motherese.

Within the first few months of life, bottlenose dolphins begin to produce unique sounds.  These bleats, chirps, and squeaks become a signature whistle - a label that conveys an identity, comparable to a human name.  While the development of a signature whistle is influenced by learning from other dolphins, each whistle varies in volume, frequency, pitch, and length.  Dr. Laela Sayigh, a Woods Hole Oceanographic Institution marine biologist, focuses her research on social behavior and communication of whales and dolphins.  She said, "[Dolphins] use these whistles to keep track of each other.  They're periodically saying, "I'm here, I'm here."  

Previous research has shown that groups of dolphins tend to develop different styles of whistling, but why dolphins develop these styles is still unclear.  In a study published in Scientific Reports, researchers collected 188 hours of acoustic data from common bottlenose dolphins in the Mediterranean Sea and then analyzed the differences in whistles between six distinct populations.  They found that, like regional accents in humans, the dolphins had similarities in their signature whistle based on where they lived.  For example, dolphins living in areas with seagrass had higher pitched and shorter signature whistles when compared to dolphins in areas where the sea bottom was muddy.  The size of dolphin populations also had an effect on the development of whistles, with smaller pods having more changes in pitch in their whistles than larger pods.

It turns out that dolphin mothers use a kind of high-pitched "baby talk" when addressing their calves.  Researchers published a study last week in the journal Proceedings of the National Academy of Sciences.  The scientists were able to record and analyze the signature whistles of 19 mother dolphins in Florida when accompanied by their young calves and also when swimming alone or with other adult dolphins.  Collecting this data was no easy feat; for more than 30 years, scientists placed special microphones multiple times on the same wild dolphin mothers in Sarasota Bay to record their signature whistles.  Researchers noted that when directing their unique signal to their calves, the mother's whistle pitch was higher and her pitch range was greater than usual.  The motherese tone appeared only to be used when the mother used their signature whistle, not when making other vocalizations.  Dr. Janet Mann, Professor of Biology and Psychology at Georgetown University who studies social learning and networks in dolphins, added, "It's really important for a calf to know 'Oh, Mum is talking to me now' - versus just announcing her presence to someone else."

The data from this study adds to the growing body of evidence that dolphins provide a powerful animal model for studying the evolution of vocal learning and language.