How do dolphins recognize their friends?

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

Study leader Jason Brook, a marine biologist at Stephen F. State University in Austin, Texas, did not investigate whether these cetaceans could identify each other from their urine. His original goal was to test whether dolphins use their signature whistle in the same way humans rely on names. But to do this, he needed to discover a second method that dolphins use to identify each other.

To find out if they could link the whistle to a specific dolphin, Brook turned to a surprising substance: urine. One day, a scientist observed wild dolphins deliberately swimming in a plume of urine, which led the biologist to suspect they were getting information from it.

“I tried,” says Brook, whose study was published in the journal. Scientific achievements. “And I didn’t expect it to work, to be honest. »

In experiments with captive dolphins, the team found that the dolphins paid more attention to their friends’ urine and whistles, suggesting they knew the animals emitting them, he says.

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

“I was shocked, just shocked. A smile appeared on my face,” says Brook, who couldn’t believe his experiment had worked.


In 2016 and 2017, Brook and colleagues observed several bottlenose dolphins at facilities designed to interact with these mammals in Bermuda and Hawaii, which also operate a consortium to breed the species. On these sites Dolphin QuestDolphins live in lagoons fed by natural sea water, which mimics their natural habitat.

The researchers’ first step was to find out if dolphins could detect urine in sea water. Over the course of evolution, bottlenose dolphins lost their sense of smell but retained a strong sense of taste.

Dolphins, temporarily separated from others, were placed in large containers. The scientists then poured water containing ice into it and then observed each person’s reaction. Curious dolphins exploring the icy water were good candidates for the experiment. Next, the team had to test whether the reactions of the animals to ice-cold water and urine differed, and whether the reactions to familiar and unfamiliar urine were the same.

By noting which dolphins had lived together for at least five years, the team learned which people knew each other and which didn’t. Therefore, the researchers poured doses of approximately 20 milliliters of urine from familiar and unfamiliar dolphins into the pool, one after the other, with the order determined at random.

Dolphins spent about three times as much time examining familiar urine as unfamiliar urine, and several individuals analyzed familiar matter for more than twenty seconds. The cetaceans paid little attention to the unfamiliar urine, analyzing it no longer than icy water.


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