Dolphins, especially social and intelligent mammals, use whistles to communicate with each other. It has even been discovered that some species are identified with ‘names’, differentiating chirps for each specimen. These exchanges of information are essential for various cooperative activities, such as hunting or breeding. However, the noise generated by human activities, such as drilling or shipping, can make these ‘conversations’ difficult and negatively affect your health. A small study, carried out with two specimens in an experimental environment, shows that dolphins ‘scream’ when they try to work together in response to increased noise levels underwater.
“The same reasons that make the use of sound so advantageous for animals also make them susceptible to noise disturbance in the environment,” says Pernille Sørensen, from the University of Bristol, UK. “In the last two decades, we have seen a dramatic increase in man-made noise, and noise pollution in the oceans is no exception,” he points out.
The two dolphins observed in the study, ‘Delta’ and ‘Reese’, were placed in an experimental lagoon and fitted with suction cup sound recorders to document their vocalisations. The controlled environment allowed them to closely follow the dolphins, something that would have been very complex in the wild.
The specimens had to work together to each press their own underwater button placed at each end of the lagoon within a second of each other. They were released from a starting point during each trial, and for certain trials, one of the dolphins was held for five to 10 seconds while the other was immediately released. In delayed release tests, the dolphins had to rely solely on vocal communication to coordinate the button press.
The researchers found that when increasing levels of noise were played from an underwater speaker, both dolphins they made up for it by changing the volume and duration of their calls to coordinate the button press. From the lowest to the highest noise levels, the dolphin success rate dropped from 85% to 62.5%. That is to say, although they tried to communicate, the excessive noise affected them in solving the task.
Dolphins, as the authors explain in ‘Current Biology’, not only changed their calls, but also They changed their body language. As noise levels increased, the dolphins were more likely to reorient themselves to face each other, and they were also more likely to swim to the other side of the lagoon to get closer.
“Our work shows that despite their attempts to compensate, despite being highly motivated and the fact that they know this cooperative task so well, the noise still impaired their ability to coordinate successfully,” says Sørensen.
While this research was conducted with dolphins living in human care, human-generated noise can also have detrimental effects on wild dolphins. “If groups of animals in the wild are, for example, less efficient at cooperatively foraging for food, this will have a negative impact on individual health, which will ultimately affect the health of the population,” says co-author Stephanie King, an associate professor at the University. of Bristol, Bristol, UK.
“Our results clearly show the need to take into account how noise affects group tasks in wild animals,” adds Sørensen.