Every bottlenose dolphin has its own distinct high-pitched whistle. The marine mammals use these whistles to identify one another and to communicate and maintain bonds. They can even mimic the whistles of close friends and family.
“A signature whistle is often said to be similar to a name because it is individually distinct and serves to identify the animal,” Brittany Jones, a researcher at the National Marine Mammal Foundation, tells NBC News’ Sarah Sloat.
Previous research has shown that groups of dolphins tend to develop different styles of whistling, but why dolphins develop these styles is still unclear, per a statement.
In a new study published in Scientific Reports, scientists found that the location and population demographics of bottlenose dolphins, genus Tursiops, influence differences in these signature whistles even more so than genetics.
Researchers collected 188 hours of recorded acoustic data from common bottlenose dolphins in the Mediterranean Sea and 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 instance, dolphins living in areas with seagrass had higher pitched and shorter signature whistles compared to dolphins in areas where the sea bottom was muddy, per the statement. Why this occurs is hinted at in the paper: “Sound transmission in shallow water is highly variable and depends on bottom sediments…temperature gradients, freshwater inputs, obstacles in the sound path and the interactive effect between the sediment and plants (such as seagrass meadows) and/or animals (like benthic in-fauna) that live on the bottom.”
The size of populations also had an effect on the development of whistles—smaller populations had more changes in pitch in their whistles than larger populations. Together, the paper concludes that both environmental conditions and the demographics of a group of dolphins contribute heavily to signature whistles.
Other studies have looked at the development of whistles in specific subpopulations, like bottlenose dolphins in the waters around Florida, Portugal and Namibia, but this study is a first for its width and breadth in study area, with a larger study area than any previous research.
“The study provides the first evidence that the genetic structure, which distinguishes the eastern and western Mediterranean bottlenose dolphin populations, has no strong influence on the acoustic structure of their signature whistles, and that the geographical isolation between populations only partially affected whistle variability,” per the authors.
The study states that data on ambient noise and vessel traffic was not available for all sites, so those factors could not be included in the research. However, previous studies have shown that high noise levels from vessels “can have a strong influence on whistle structure,” the authors write, though noise alone is not enough to explain differences in whistles.
“I would like people to reflect on the importance of the acoustic environment in which dolphins live for the development and maintenance of their communication,” study lead author Gabriella La Manna, a marine biologist at the University of Sassari in Italy, tells Earth.com’s Andrei Ionescu. “Human activities, such as commercial shipping and nautical traffic, can severely affect this fundamental aspect of dolphins’ life. ”
Another recent study showed that bottlenose dolphins also recognize each other from the taste of their urine.