Most of us can recognize our friends using at least two of our senses: You probably know your buddy's face and the sound of their voice, for example. For more intimate relationships you might even know the smell of their deodorant, perfume or other signature scents.
But dolphins bring another sense to the identification game. New research suggests the marine mammals actually know the taste of their friends. More specifically, they can recognize comrades by sampling their urine.
"Our study presents the first case of identity perception by taste alone in animals," reads a paper by researchers from the University of St. Andrews in the UK that was published in the journal Science Advances on Wednesday.
It's long been known that individual dolphins can identify themselves and others by their unique signature whistles, but the new research shows dolphins can track their friends' coming and going through taste.
"The use of taste is highly beneficial in the open ocean because urine plumes will persist for a while after an animal has left," the study reads.
Researchers worked with dolphins at Dolphin Quest facilities in Bermuda and Hawaii. They found that when they were exposed to samples of urine from other dolphins they lived with, they would linger three to four times longer than they would with urine samples from unfamiliar dolphins.
In another phase of the experiment, the scientists played either the matching signature whistle of the dolphin whose urine was being sampled or the whistle of a different, mismatched dolphin. This is a little like showing someone a picture of a friend while playing either a clip of their voice or a clip of someone else's voice.
Again, the dolphins lingered longer with the urine sample when it matched the whistle of the dolphin it came from. All this suggests dolphins taste pee to see who's who in the same way dogs sniff butts.
In case you were wondering if dolphins might be using their sense of smell rather than taste, it's a little-known fact that dolphins have an underdeveloped sense of smell and studies have suggested that their sense of taste is limited to saltiness. Perhaps this helps them distinguish a buddy's pee from the surrounding salt water ocean.
"Given the recognition skills revealed in our study, we think that it is likely that dolphins can also extract other information from urine, such as reproductive state, or use pheromones to influence each other's behavior," the researchers explain, adding that the findings suggest dolphins are able to identify and label objects, which "may be used in mental operations such as planning, mental time travel, or the simulation of social scenarios."
In other words, the research adds to a large, existing pool of evidence showing that dolphins are remarkably smart creatures. The surprising revelation, though, is that the best way to introduce yourself to one next time you go for a swim with dolphins might be to pee in the pool.