When adult humans meet a cooing infant, many can’t help themselves: They begin speaking in a higher-pitched, sing-songy voice.
Known as parentese, or infant-directed speech, this subtle shift is not unique to humans—it has also been observed in rhesus macaques, squirrel monkeys, zebra finches and gorillas. Now, scientists are adding one more species to that list: bottlenose dolphins.
Dolphins communicate in a unique way: Every individual produces its own signature sound that functions much like a nametag or an ID card. But how does each dolphin come up with its distinctive whistle? For calves, it might have something to do with listening to Mom. So, to start unraveling this mystery, researchers examined the sounds mother dolphins make.
Scientists analyzed 34 years’ worth of audio recordings that captured sounds made by 19 female bottlenose dolphins living near Sarasota Bay, Florida. When the mother dolphins were near their calves, they continued to make their signature whistle sound, but they did it at a higher frequency. They also used a wider overall range of frequencies than they did when their calves were not nearby, according to a new paper published Monday in the journal Proceedings of the National Academy of Sciences.
Do you hear the pitch change between these 2 whistles? It's a bottlenose dolphin mom using "baby talk!"— Woods Hole Oceanographic Institution (WHOI) (@WHOI) June 27, 2023
Find out more about #WHOI biologist Laela Sayigh's study in @PNASNews from @AP: https://t.co/A8yZWUqB80
Sarasota Dolphin Research Program, NMFS MMPA Permit 20455 pic.twitter.com/GnKRNzgWrL
This discovery suggests that “using these modifications when communicating with young assists them in learning how to produce these calls themselves,” as Rindy Anderson, a behavioral ecologist at Florida Atlantic University who was not involved in the study, tells National Geographic’s Carrie Arnold.
At the very least, the higher-pitched whistle likely gets the calves’ attention.
“It’s really important for a calf to know, ‘Oh, Mom is talking to me now,’ versus just announcing her presence to someone else,” says Janet Mann, a marine biologist at Georgetown University who was not involved in the research, to the Associated Press’ (AP) Christina Larson.
The findings help shed more light on how dolphins communicate. But they may also someday have broader implications for understanding the evolution of vocal learning and language development in animals, including humans, per New Scientist’s Chen Ly.
It’s not totally clear why humans and other species use a higher-pitched voice when speaking to their young. However, some research suggests it could help babies learn how to talk. Since dolphins are also a “highly acoustic” species, and calves often spend between three and six years with their mothers before venturing off on their own, it makes sense that this adaptation would also help them learn to communicate, as study co-author Frants Jensen, a marine biologist at Aarhus University in Denmark, tells the AP.
“The idea that there might be similar forces driving [parentese] in such different species is just really cool,” says study co-author Laela Sayigh, a marine biologist at the Woods Hole Oceanographic Institution, to Science News’ McKenzie Prillaman.
With more research, scientists could add support for this finding and determine the extent of dolphins’ baby talk. “I would be really interested to see whether dolphins also change their whistles when interacting with babies of others, which is what happens in humans,” Julie Oswald, a biologist at the University of St Andrews in Scotland, tells New Scientist.