How do dolphins recognize their friends?

We humans rely on a number of characteristics to recognize our friends, such as their smile, their voice, or the way they walk. Biologists have known for decades that dolphins form close friendships and identify friends by their unique whistles. Now, a startling new study suggests that bottlenose dolphins Tursiops use their sense of taste to distinguish their friends’ urine from that of strangers.

Study leader Jason Bruck, a marine biologist at Stephen F. State University in Austin, Texas, did not investigate whether these whales could identify each other by their urine. His original goal was to test whether dolphins use their distinctive whistles in the same way that humans rely on names. But to do that, he had to discover another method that dolphins use to identify each other.

To find out if they could associate a whistle with a particular dolphin, Bruck turned to a surprising substance: urine. A scientist once observed wild dolphins deliberately swimming in urine veneers, leading the biologist to suspect that they were getting information from them.

“I gave it a shot,” says Bruck, whose study was published in the journal The progress of science. “And I did not expect it to work, to be honest. »

In experiments with dolphins in captivity, the team found that the dolphins were more aware of their friends’ urine and whistles, suggesting that they knew the animals sending them out, he says.

These results are the first strong evidence that an animal identifies other members of its species by taste. They also show that by using at least two characteristics to identify individuals, dolphins have a complex understanding of their family and friends, just like humans.

“I was in shock, just in shock. My smile went over my face,” says Bruck, who could not believe that his experiment had worked.

ENTHUSIASTIC PARTICIPANTS

In 2016 and 2017, Bruck and his colleagues observed several bottlenose dolphins at facilities designed to interact with these mammals in Bermuda and Hawaii, which also run a breeding consortium for the species. In these sites of Dolphin Questdolphins live in lagoons fed with natural seawater, which simulates their environment in nature.

The researchers’ first step was to see if dolphins could detect urine in seawater. Over evolution, bottlenose dolphins lost their sense of smell but retained a strong sense of taste.

Dolphins temporarily separated from others were placed in large tanks. The researchers then poured water with ice into it and then observed each individual reaction. Curious dolphins exploring the icy water were good candidates for the experiment. Next, the team had to check whether the animals’ reactions to ice water and urine were different, and the same for known urine and unknown urine.

Noting which dolphins had lived together for at least five years, the team knew which people knew each other or not. So the researchers poured doses of about 20 milliliters of well-known and unknown dolphin urine into the tank, one after the other, and the order was determined at random.

The dolphins spent about three times longer examining known urine than unknown urine, and a few individuals analyzed the well-known substance for more than twenty seconds. Whales paid little attention to unknown urine and analyzed it no further than ice water.

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