Bottlenose dolphin mothers modify signature whistles in the presence of their own calves

Human caregivers interacting with children typically modify their speech in ways that promote attention, bonding, and language acquisition. Although this motherese, or child-directed communication (CDC), occurs in a variety of human cultures, evidence among nonhuman species is very rare. We looked for its occurrence in a nonhuman mam-malian species with long -term mother-offspring bonds that is capable of vocal production learning, the bottlenose dolphin (Tursiops truncatus). Dolphin signature whistles provide a unique opportunity to test for CDC in nonhuman animals, because we are able to quantify changes in the same vocalizations produced in the presence or absence of calves. We ana-lyzed recordings made during brief catch- and-release events of wild bottlenose dolphins in waters near Sarasota Bay, Florida, United States, and found that females produced signature whistles with significantly higher maximum frequencies and wider frequency ranges when they were recorded with their own dependent calves vs. not with them. These differences align with the higher fundamental frequencies and wider pitch ranges seen in human CDC. Our results provide evidence in a nonhuman mammal for changes in the same vocaliza-tions when produced in the presence vs. absence of offspring, and thus strongly support convergent evolution of motherese, or CDC, in bottlenose dolphins. CDC may function to enhance attention, bonding, and vocal learning in dolphin calves, as it does in human children. Our data add to the growing body of evidence that dolphins provide a powerful animal model for studying the evolution of vocal learning and language.

Automated summary

Human caregivers modify their speech to promote attention and language acquisition in children. This phenomenon, known as motherese or child-directed communication (CDC), is rarely observed in nonhuman species. However, a study on bottlenose dolphins found that female dolphins produced signature whistles with higher frequencies and wider pitch ranges when recorded with their calves, similar to human CDC. This provides evidence for convergent evolution of CDC in dolphins and suggests that it may serve similar functions in enhancing attention, bonding, and vocal learning in dolphin calves as it does in human children.