Scientists have discovered that bottlenose dolphins can recognize each other through taste. Specifically, the taste of their urine.
Published this week in the journal Science Advances, the paper, by researchers at Stephen F. Austin State University, Texas, and University of St. Andrews, Scotland, found that dolphins can identify other individual dolphins just through the taste of their pee.
The researchers discovered this while they were trying to find out more about dolphins’ “signature whistles”: the specific calls they develop to refer to themselves. Jason Bruck, one of the study’s authors, explained to Motherboard: “[Dolphins] essentially, come up with their own name” but researchers didn’t know whether these work in the same way as human names. “If I name your best friend, you’ll picture them in your head, right?” The scientists wanted to know if dolphins similarly recognize others’ names.
They tested this by matching the whistles to a different sense. A human will use the same word to describe something—say, a mug—whether they see, hear, or feel it. “That’s what we were trying to get at,” Bruck said.
To do this, they needed to “match and mismatch” the whistle to a different sense, as another way of identifying the animal. If another dolphin responded more to the match or the mismatch, it would show they knew which individual it belonged to.
They briefly floated (no pun intended) the idea of waterproofing a high-definition TV screen to explore visual cues. “But that would have been very heavy, very expensive, and very hard to move around,” said Bruck.
That’s where the urine comes in. The scientists recalled anecdotes of dolphins swimming through “excretion plumes” (that’s piss, to you and me) with their mouths open. Dolphins can’t smell—because they don’t have an olfactory bulb—so the researchers theorized they must somehow use the taste of urine to gather information about its owner.
After collecting samples from dolphins in lagoons in Bermuda and Hawaii (which had been trained to give urine for health assessments), they put the pee “in a little cup at the end of a very long pole” and poured it in front of a dolphin while playing the whistle of another dolphin. Researchers measured how long the dolphins “sampled” the piss—opening their mouths and running their tongue through the water—and if the dolphins’ responses changed when the pee came from a familiar or unfamiliar dolphin.
Dolphins kept their mouths open longer when encountering the urine of an individual that was familiar to them. When the urine sample also matched the correct signature whistle for the dolphin it came from, they hovered around the underwater speaker for longer than when the sound and the pee did not match. This told them that dolphins can recognize others through taste alone: something no other vertebrate has been shown to do. “So that's a big deal,” says Bruck.
Laela Sayigh, a marine biologist at Woods Hole Oceanographic Institute, who was not involved in the study, told National Geographic that these findings open doors to other questions around what they might be learning from urine trails.
There are lots of “powerful avenues for future research,” Bruck agreed. More research is needed, so, it sounds like he and the team may be pouring wee over dolphins for a while longer.