Noise pollution make dolphins “shout” to communicate with earth other

(Dolphin Research Center, Florida, USA https://bit.ly/3WpKuNX)

Noise pollution makes it difficult for bottlenose dolphins to perform tasks that require cooperation between several individuals.

In such conditions it is difficult for dolphins to “talk”, so they cannot coordinate their actions normally.

Bottlenose dolphins try to solve this problem by emitting louder and longer calls, but this is not enough to compensate for the anthropogenic noise.

This is further evidence of how noise pollution is negatively affecting cetaceans.

Cetacean mammals live in a world of sounds. For example, dolphins use ultrasound to locate prey and navigate in space.

In addition, they developed a complex system of communication with relatives.

However, human activity in the ocean is making it increasingly noisy, which significantly complicates the life of dolphins and whales.

Now it is more difficult for them to hear each other and detect a predator or prey.

In addition, loud noise frightens some cetaceans, forcing them to refuse feeding and interrupt their rest.

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NOISE
Now, a team of zoologists from the University of Bristol decided to learn more about how noise pollution affects dolphin communication.

Previously, researchers had demonstrated that captive bottlenose dolphins (Tursiops truncatus) can solve problems by working in pairs.

These cetaceans successfully passed experiments in which two individuals had to simultaneously press buttons at opposite ends of the lagoon.

To coordinate actions, dolphins communicated with each other with the help of whistles.

In a new study, the team led by Pernille M. Sørensen repeated these experiments under simulated anthropogenic noise.

Two male bottlenose dolphins, Delta and Reese, were asked to solve the task of simultaneously pressing buttons in normal background noise and under the influence of noise of 119.126, 135 and 150 decibels, which was played from the speaker.

In total, the authors conducted 200 trials, 40 for each sound mode. It turned out that the louder the ambient noise, the worse bottlenose dolphins cope with solving the problem.

At normal noise levels, their success rate was 85%, and at the highest noise level, 62.5%.

During the experiments, Delta and Reese made a total of 251 whistles.

Among them were individual whistles, the frequency was 4-18 kilohertz for Delta, and 6-20 kilohertz for Reese.

As the intensity of the ambient noise increased, both individuals had to increase the volume of the signals they produced.

In response to a one decibel increase in ambient noise, Delta increased the volume of whistles by 0.08 decibels, and Reese by 0.14 decibels.

Also, under conditions of noise pollution, both dolphins began to emit longer whistles.

This dependence was significant only for Delta, which increased the duration of signals by 7.2 milliseconds in response to an increase in ambient noise by one decibel.

This is in line with previous studies showing that humpback whales (Megaptera novaeangliae) increase the duration of their songs when exposed to low-frequency sonar

At the same time, killer whales (Orcinus orca) emit longer calls due to ship noise.

In addition, Reese reduced the speed of the whistles in response to the increased volume of the noise. Both dolphins also used echolocation less frequently in noisy environments.

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DOLPHINS ADAPT
Noise has affected more than just the signals produced by dolphins.

Sørensen’s team noticed that the higher the noise level, the more often each individual turns towards the partner. So Delta and Reese increased the chances of hearing each other.

In response to noise pollution, dolphins also spent more time near their partner.

This probably allowed them to hear it and take advantage of additional visual cues.

The results of the study show that noise pollution has made it harder for Delta and Reese to hear each other and coordinate their activities.

As a result, the percentage of successfully passed tests decreased.

Although the dolphins tried to solve this problem by changing the volume and duration of the sound signals, they were not able to fully compensate for the effect of noise.

The researchers emphasize that wild dolphins, which live in conditions of severe anthropogenic pollution, are likely to face similar problems.

Sources:

• Current Biology: https://www.cell.com/current-biology/fulltext/S0960-9822(22)02000-0
• University of Bristol: https://www.bristol.ac.uk/news/2023/january/dolphins-affected-by-human-made-noise.html
• ScienceDaily: https://www.sciencedaily.com/releases/2023/01/230112113208.htm

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#science #animals #dolphins #communication #noise #news #nftmc