Reference: La Manna, G., Rako‐Gospić, N., Sarà, G., Gatti, F., Bonizzoni, S., & Ceccherelli, G. (2020). Whistle variation in Mediterranean common bottlenose dolphin: The role of geographical, anthropogenic, social, and behavioral factors. Ecology and evolution. DOI: 10.1002/ece3.6029.
Have you ever wondered what animals are saying when they make noise? Many different species, including species of insects, frogs, birds, fish, and mammals, have their own languages. They make different sounds to communicate different things. Sound can be used for communication during activities like hunting, reproduction, and territory defense. While members of the same species generally communicate in the same way, the exact sounds that they make vary depending on factors such as their physical environment and genetic differences between individuals.
One particular species that uses sound to communicate is the bottlenose dolphin. They use whistles to recognize each other, maintain contact with each other, and to coordinate with their groups. While all dolphins use whistles to communicate with each other, different populations of dolphins have different-sounding whistles. They vary in pitch, length, and inflection points. A team of researchers Gabriella La Manna from MareTerra Onlus set out to further investigate the factors that cause different populations of dolphins to have different whistles. They chose to study whistle variation between bottlenose dolphins in Sardinia and Croatia, because although previous studies had already identified different whistles between the two populations, scientists had not yet understood where these differences came from.
La Manna and their team started by studying the physical environment surrounding each group of dolphins. They observed noise levels and the amount of boat traffic as well as socio-behavioral factors such as dolphin behavior, group size, and the presence of dolphin calves. They also recorded the dolphins’ whistles at each location and matched the type of whistle with an observed behavior. Using this data, they could determine if there is a correlation between environmental factors and the whistle differences.
The researchers found that with the presence of calves, whistles in Croatia were higher pitched, but were lower pitched in Sardinia. However, when the researchers controlled for group size and activity, they found similar pitch characteristics between populations. Besides pitch, the researchers also looked at other characteristics of whistles including the duration, number of inflection points (or when the pitch goes up and down), and the range of pitch. They found that all of these increased as the size of the group increased for dolphins in both locations, but were overall lower in Sardinia than in Croatia. In Croatia, with more environmental noise, the whistles sounded higher pitched and in Sardinia, with more boat traffic, the whistles sounded higher pitched. In short, the way that dolphins modulate their whistles in response to environmental changes seems consistent for both populations, although the dolphins in Sardinia have a baseline lower pitch.
Since some whistle characteristics varied between the populations and other studies have recorded genetic differences between them, it is likely that the two populations do not have much, if any, contact with each other. Therefore, some of the differences in their whistles are likely because of their lack of contact with each other, which shows that different populations of dolphins naturally communicate in slightly different ways. The changes in their whistles in response to increased noise and boat traffic show that they are adapting independently to their physical environment to communicate more effectively.
Why do we need to know what influences communication in dolphins? Understanding the factors that influence how dolphins communicate, such as geographic location and group size, helps us to see how their communication changes when humans come into the picture, like through increased environmental noise or boat traffic. Noise in the environment is increasing, and it can impact animals’ behavior and health. Observing changes in communication based on changes in their habitat caused by people can help us to understand the effects we have on the environment, and maybe even reduce them.