Love it or hate it, but the way humans modify their speech when they communicate with their young offspring, commonly known as "baby talk," has now been recorded among bottlenose dolphin mothers, too.
Also known as motherese, child-directed communication (CDC) features a higher pitch and wider pitch range, believed to boost bonding and language learning in children.
Researchers found that wild bottlenose dolphins (Tursiops truncates) near Sarasota Bay, Florida, changed their signature whistles – their individual "voice" – to a higher frequency with a greater range, essentially demonstrating CDC, when they were in the presence of their calves.
“It has been well documented that dolphins are capable of vocal production learning, which is a key aspect of human communication,” said journal article co-lead author Nicole El Haddad. “This study adds new evidence regarding similarities between dolphins and humans. With that said, I’m hopeful that this interesting finding could increase awareness in the general public about the protection of this charismatic species.”
The scientists analyzed the recordings of 19 adult female dolphins, from a pod that's been studied for more than 50 years for various research projects. While briefly caught for health assessments, the dolphins were fitted with temporary hydrophones on suction caps attached to their heads.
Researchers have for a long time been trying to find a way to decipher complex dolphin language and communication. The recordings that resulted from this study revealed how much the signature whistle varied when the mothers were around their calves.
“This paper could be a springboard, inspiring other scientists to focus on child-directed communication in other species,” El Haddad said. “It would be interesting to compare vocal aspects of different marine mammal mothers in [the] presence of their offspring.”
Scientists don’t know a lot about CDC in other species. Adult male zebra finches (Taeniopygia guttata) adjust their songs when juveniles are nearby, while squirrel monkeys (Saimiri sp.) and rhesus macaques (Macaca mulatta), alter their vocalization when communicating with younger members of their species. Of course, it’s much more subtle than the broad range humans use when talking to children.
“It’s really exciting to find evidence for CDC in another mammalian species, even if we can’t necessarily speak to its function in dolphins,” said journal article co-lead author Laela Sayigh, a biologist at the Woods Hole Oceanographic Institution (WHOI). “The fact that dolphins use motherese is an excellent example of what we call convergent evolution.”
Convergent evolution, or how disparate species spread across geographic areas either adopt or retain similar traits, is a fascinating area of study for biologists.
The study “reveals an intriguing case of convergent evolution as female bottlenose dolphins modify individual vocalizations in the presence of their calves, mirroring the acoustic changes observed in human motherese,” said Frants Havmand Jensen, a senior scientist at the Department of Ecoscience at Aarhus University, Denmark, and a guest investigator at WHOI.
“Our findings also have the potential to enhance population monitoring efforts,” added Jensen. “We are developing tools to listen for the unique whistles of individual animals. If we could reliably detect the subtle changes in signature whistles when calves are present, then we can use that to understand reproductive success and overall population health of wild dolphins.”
Listen to an example of one of the recorded signature whistles, slowed down eight times in order to make these high frequency sounds audible to human ears, below.
The research was published in the journal Proceedings of the National Academy of Sciences (PNAS).
