In the early months of their lives, young dolphins display their creativity and create a unique sound. These unique sounds, which include chirps, bleats and squeaks, are a new possession in the animal kingdom. They convey an identity similar to a human name.
These labels are known as signature whistles and play an important role in maintaining and creating relationships among dolphins. Although the signature whistle is developed from information gleaned from dolphins, every whistle is unique in its volume, frequency, and length.
Over 50 years of research into signature whistles has led scientists to make significant advances in our understanding of how and why whistles are used. What is less known is the precise factors that affect these different styles and how they broadcast the existence of a single creature.
A new study on dolphins in Mediterranean Sea claims that there are two factors that best explain differences between signature whistles. These are the local environment and the demographics among different dolphin populations.
Scientists discovered that dolphins that live in areas with more seagrass have shorter signature whistles than those that live in areas with a deeper seafloor. Dolphins living in smaller groups were able to change their pitch more frequently than those in larger groups.
These results were published in Scientific Reports. They support the theory that dolphins make signature whistles that are most appropriate for their habitat.
Brittany Jones, a postdoctoral researcher at the National Marine Mammal Foundation, said that a signature whistle is often compared to a name. She said this because it serves to identify the animal.
Jones explained that signature whistle owners use it more than other dolphins. However, other people use our names less often than we do. Jones also said that signature whistles are similar to our distinct voice, which can communicate information about identity, proximity, and emotional states.
Researchers discovered that dolphins mimic the signature whistle of another dolphin to establish contact. Sometimes, they even add parts to their signature whistle. A 2018 study of male bottlenose dolphins revealed that they keep their “names” throughout adulthood, just as females. It was previously believed that males abandon their signature whistle in order to adopt the same whistle for their alliance groups.
Scientists believe that dolphins, like humans and possibly elephants, are capable of long-term social recognition. Jason Bruck, an assistant professor from Stephen F. Austin State University, stated that dolphins can recall other dolphins by their whistles even after long periods of inactivity.
Bruck was not part of the research, but is the first author in a Science Advances study that revealed bottlenose dolphins can identify each other through signature whistles and unique tastes of their urine.
Bruck stated that dolphins can be identified by at least two social methods, which include urine cues and signature whistles. “Dolphins can mimic whistles, if they wish to, so urine may be more resistant to cetacean identification theft, but deception in signature whistles is still understudied.”
Scientists analyzed 188 hours worth of recorded acoustic data from different research groups between 2006 and 2020 to study the dolphins in the new paper. These sounds were captured at six locations in the Mediterranean Sea which is divided into east and west basins. The study team wanted to determine if signature whistles could be influenced by genetic variation. The eastern and western basins were therefore used to determine genetic variation.
The team extracted 168 whistles from the recordings, and analysed their acoustic characteristics in relation to several factors. These included the exact location of the whistle, whether it was in the eastern or Western basin, the local environment, and the population demographics.
The scientists concluded that the location of the dolphins only had a partial effect on whistle variability and that the genetic differences between them had no significant influence on the acoustic structure their signature whistle.
However, signature whistles were strongly affected by environmental and demographic factors. These findings are consistent with the “acoustic adapt hypothesis,” which suggests that animals acoustically adapt vocalizations to local conditions in order to maximize their purpose. These are the main influences on signature whistle variability, and they can be used to influence each other and invent their own sounds.
Bruck stated that “there might be aspects to these calls that dolphins are paying attention that we weren’t aware of.” There is a possibility that signature whistle styles could be different between dolphins due to anatomical differences. Genetics would ultimately explain these differences. We don’t yet know the answer. Scientists can examine captive dolphins to make it possible to design more comprehensive studies, he says. However, this is much more difficult in the wild.
We know more about dolphin communication systems in captivity than we do in the wild. There is still much to be learned. In captivity, signature whistles are most common when a dolphin is separated from its group. Signature whistles are a significant part of the dolphin’s repertoire. They make up between 38 and 70 percent of its total whistle repertoire in the wild.
Jones stated that studies of signature whistle recordings have provided valuable insights into how dolphins communicate, bond and reunite in murky water. She is now interested in finding out if signature whistle recordings can be used to predict changes in health status.