A study has found that dolphins are unable to communicate as effectively when exposed to human-generated noises, forcing them to change their sounds much like people do when shouting.
An international team of researchers from the University of Bristol, the Dolphin Research Center, Syracuse University, the Woods Hole Oceanographic Institution, Aarhus University, and the University of St. Andrews collaborated on the study, which was published in Current Biology on Thursday
“We wanted to investigate how noise impacts animals working together,” said Pernille Sørensen, first author of the paper and PhD candidate at the University of Bristol, in an interview with CNN. “So basically looking at the whole communication network, from a sender to a receiver and whether there is any impact on that transmission.”
Previous studies have documented the damaging impact that noise pollution can have on other aquatic mammals, like whales. The constant din of noises from ship engines and military sonar makes it difficult for marine mammals to communicate with each other and has been linked to increasing collisions between whales and ships.
The researchers honed in on dolphins because the aquatic animals are highly social and intelligent, using whistles to communicate with each other and clicks to echolocate and hunt. And sound communication is particularly crucial for underwater animals because beneath the water’s surface, “sound travels very far and very fast,” said Sørensen.
Additionally, dolphins have a “wide vocal repertoire” that they employ “for basically all aspects of their lives, including for coordinating cooperative behaviors.”
To understand how noise pollution affects dolphins’ ability to cooperate, the scientists worked with two specific dolphins named Delta and Reese living at the Dolphin Research Center in Florida. The dolphins had a mission: They needed to each press an underwater button at the same time. The dolphins were asked to perform the task both under ambient noise conditions and under four “noise treatments” meant to simulate human-made underwater noise pollution. A total of 200 trials were conducted with the dolphin pair, with each dolphin wearing an acoustic tag that recorded its sound production.
The findings were twofold, said Sørensen. First, they found that the dolphins used “compensatory mechanisms” to make up for their hindered vocal communication. As the underwater noise increased, made louder and longer sounds, and changed their body language to face each other.
But the more important finding, according to Sørensen, was that despite using their attempts to compensate for the noise pollution, the dolphins were still less successful at completing the task. Their success rate dropped from 85% to 62.5% from the lowest to highest levels of noise.
“We’re showing, to our knowledge for the first time, that animals working together are impacted and that compensatory mechanisms are insufficient to overcome the impacts of noise,” she explained.
This might have real-world impacts on dolphins in the wild, who rely on cooperation to forage and reproduce. “They need sound in order to connect,” she said.
Sørensen added that the researchers would “absolutely have loved to introduce or include more dolphins in our experiment” and that future experiments might expand the sample size to a larger group of dolphins.
Additionally, more research is needed into the specific kinds of whistles and sounds the dolphins use for cooperative tasks.
“This research definitely contributes as a part of the puzzle to our knowledge of how noise pollution impacts animals,” said Sørensen.
She said that she hopes the research helps support “solutions for how we can better manage the noise in our oceans.”