[Animals] Dolphins can identify their friends by taste

[#Wittels-]

A study reveals that these marine mammals use cues, including unique whistles and the taste of urine, to form a complex awareness of others in their minds.

A baby bottlenose dolphin explores an ocean-fed lagoon at Dolphin Quest Bermuda.

 

We humans rely on a set of cues to recognize our friends, such as their smiles, their voices, or the way they walk. Biologists have known for several decades that dolphins form close friendships, and that cetaceans identify their mates by their unique whistles.

Now surprising new research suggests that bottlenose dolphins use their sense of taste to discern their friends' urine from that of other dolphins.

Study leader Jason Bruck, a marine biologist at Stephen F. Austin State University in Texas, was not looking to test whether bottlenose dolphins could identify each other through their urine: his original goal was to test whether they use their characteristic whistles in same way people are based on names. But for that, you need a second way for the dolphins to identify each other.

To find out if the dolphins were able to associate a whistle with a specific dolphin, Bruck turned to an unlikely substance: urine. A scientist had previously observed wild dolphins purposefully swimming through urine plumes, leading the specialist to suspect they were gathering information from her.

 

"It was a shot in the dark," says Bruck, whose study was published this week in the journal Science Advances. "And I didn't expect it to work, to be honest."

In experiments with captive dolphins, the team found that these marine mammals paid more attention to the urine and whistles of their friends, suggesting that they knew the animals that emitted them, he explains.

The findings are the first solid evidence of an animal identifying other members of its species using taste. They also show that, by using at least two cues to identify individuals, dolphins have a complex understanding of their family and friends, just like humans.

"I was shocked, just shocked," says Bruck. "I had a big smile on my face, like, my God, this hides."

watching the dolphins
In 2016 and 2017, Bruck and colleagues observed several bottlenose dolphins at dolphin interaction facilities in Bermuda and Hawaii that also maintain a breeding consortium for the species. In these Dolphin Quest locations, the dolphins live in lagoons fed by natural seawater, which simulates their environment in the wild.

 

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

In expansive pools containing temporarily separated dolphins, scientists poured ice water into the water and then watched how each animal responded. Curious dolphins exploring the icy water were good candidates for the experiment.

 

Next, the team needed to test whether the animals' reactions to ice water and urine varied, and whether they responded differently to familiar versus unfamiliar urine.

The team knew which dolphins were familiar with one another based on who had lived together for at least five years. So the researchers saw about 20 milliliters of familiar and unknown dolphin urine in the pool, one after another, with the order determined by the toss of coins.

The dolphins spent about three times as much time investigating the familiar urine as the unknown urine, with some individuals sampling the familiar substance for more than 20 seconds. The cetaceans paid little attention to the unknown urine, drinking it only for as long as they had ice water.

"The dolphins were very, very interested in participating," says Bruck, who added that they were not rewarded with food. "Usually the dolphins get bored with my experiments. We were taking advantage of something that is part of the dolphin world."

Cetacean expectations: this was the test for the dolphins
The final test investigated whether the other dolphins had a matched understanding of other dolphins' cues — in words, whether an individual's whistle and urine were connected in their minds.

To do this, Bruck did what behavioral ecologists call an "expectation violation" experiment: show the animals something that doesn't make sense and see how they react. In people, this would be like seeing your best friend's face, but hearing a different voice.

 

For this final experiment, the biologist tested different combinations of urine and whistle on 10 dolphins, five of which were the same animals in the previous trials.

When the wrong combination of urine and whistle was exposed, the dolphins didn't pay much attention, perhaps a useful innovation for nature, where mammals would be inundated with mismatched whistles and urine, he says.

But when a dolphin encountered the correct pair of urine whistles, the animal explored the area for an average of 10 seconds longer than the mismatched pair. Two individuals stayed for more than 40 seconds: the convincing evidence that the team needed for them to be able to recognize their friends.

the taste of success
"It is very difficult to demonstrate that a concept exists in the mind of an animal, so these types of experiments that try to answer that question are very interesting and useful," says Bruno Díaz López, chief biologist at the Bottlenose Dolphin Research Institute, with based in Spain, who did not participate in the study.

Lopez, who would like to see similar studies used in the wild, adds that "it's a good approach and a good first step" in understanding the role that taste might play in dolphin recognition.

 

Link: https://www.nationalgeographicla.com/animales/2022/05/los-delfines-pueden-identificar-a-sus-amigos-por-el-gusto