Dolphins shout to each other over loud noises

Many animals rely on sounds to communicate; but we invade their habitats we generally make a noise, which has the potential to be highly disruptive, particularly in habitats like the oceans where sounds travel a very long way. To find out how animals are affected and to what extent they can compensate, a team at Florida’s Dolphin Research Centre watched as pairs of dolphins were tasked with pressing buttons at either end of their lagoon within a second of each other to get a reward. The animals had to “talk” to each other underwater to coordinate their button pushes, and the team recorded these vocalisations to see how the animals responded as the task was made more and more difficult by playing noises from an underwater speaker. The dolphins upped their game, “shouting” to overcome the din and turning to face each other underwater, but their success rate still dropped significantly as Will Tingle heard from Bristol University’s Pernille Sørensen…

Pernille - Before diving into the study, what we already knew from studies on wild animals was that animals are able to compensate for noise by using different strategies to accommodate for noise. However, up until now, we've only looked at this at the individual level, whereas what we wanted to investigate was how noise impacts animals working together And basically look at the whole communication network. Is a receiver able to receive the sound from a sender when noise is impacting them? So we set up to test this with the dolphins and what we found, what they tried to compensate by both increasing the loudness of their sounds and they also increased the duration of their calls. But despite the use of these compensatory mechanisms, we still saw that they were less successful in performing this cooperative task. All of these different noise treatments that we exposed them to actually all impacted the dolphins ability to communicate during this task a little bit. It was kind of like the higher the noise got, the more they were impacted. So we saw the biggest difficulties for the dolphins in the very high noise treatment, but also in the high noise treatment tasks.

Will - To bring this out into the wider world. Globally speaking, there's a huge number of marine vessels and boats in the world. Some estimates put them at 3 million pleasure vehicles and all these boats on the water have an effect on cetaceans like whales and dolphins in that it's a very loud noise for them. So there are dolphins and whales out there that perhaps are trying to communicate but are being blocked off, particularly in heavy shipping routes by these loud noises being made by marine vessels. So does this study have ramifications for wild species as the number of marine vessels continues to increase?

Pernille - Yes, I think it could definitely have implications for wild animals. Our findings clearly highlight that we need to account for how noise may affect animals that work together in the wild. So up until now, what we have known a lot about is that lots of animals throughout both marine and terrestrial habitats are able to perform these compensatory mechanisms in response to noise. But what we didn't know was how well those compensatory mechanisms actually worked. So this is what our study really shows, that it does have an effect of animals working together and they are less successful when noise is present. And because cooperation is common, not only in dolphins, if noise directly makes animals in the wild less efficient at working together, such as when they're performing, for example cooperative foraging, then this could really have important negative consequences not only for the individual but even at a population level.

Will - I spoke to someone on another dolphin study recently who said that the degradation of dolphin habitat would cause a reduction in the complexity of dolphin behaviour as they have less time to interact socially if they need to spend more time finding food. Language is a very complex behavior. So could we see the same thing happening here in parts of the ocean with an increased volume?

Pernille - I think that's a really interesting thought. Especially, you know, you can imagine even with us, if we are trying to communicate something to friends in a noisy environment. We might think that okay, actually maybe I need to reduce the complexity of this message because otherwise they won't understand what I'm saying. So I think that's a very interesting thought that maybe animals in the wild might similarly have to reduce the complexity of the message that they're sending on to friends in the environment simply because they cannot get the message through if they don't. I don't know if that's gonna happen, but you could imagine that there might definitely be a change in how animals work together and they need to adapt in order to continue doing these behaviors.

Will - Obviously dolphins have a complex language, but do you think there are other organisms that potentially might suffer the same consequences?

Pernille - Yeah, absolutely. Within marine mammals, we definitely see cooperative behavior across different marine mammal species. But a lot of studies have also focused on songbirds and we know that birds that live closer to very busy roads do actually call louder in order to hear each other there compared to the same species further into the woods or forest where they're not disturbed in the same way. They already show this kind of compensatory mechanism. So yes, absolutely. Other animals that are trying to work together in certain ways. I'm sure we would be able to find evidence that they would also be having issues like we see it with the dolphins.