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Bottlenose dolphins can recognise familiar individuals just by tasting their urine, similar to how the smell of a friend’s perfume can be part of our mental representation of them.

at Stephen F. Austin State University in Texas and his colleagues found that bottlenose dolphins (Tursiops truncatus) spent about three times longer sampling water that contained urine collected from familiar dolphins compared with unfamiliar ones, suggesting they recognised their friends’ unique urine tastes.

This sampling involved “opening their mouths and running their tongues through the water where we poured the urine in front of them”, says Bruck.

Bottlenose dolphins are also known to identify each other through signature whistles that they invent early in life. The latest finding indicates they can recognise each other in more than one way – either through taste or sound.

Interestingly, the dolphins were found to investigate areas for longer when they could taste a friend’s urine and simultaneously hear their whistle played through a speaker, compared with when the whistle of another known individual was played.

It suggests they have concepts of individual friends in their minds that connect their unique taste and sound, says Bruck. This is similar to how we have mental representations of our friends that integrate multiple elements like the smell of their perfume and the sound of their voice.

“While that might sound easy to do for a human, animals don’t always do that,” says Bruck.

Being able to identify other dolphins through urine is useful because it hangs around, he says. “If the urine cue can persist, then another dolphin would be able to detect that and determine if a past ally or enemy is in the area,” says Bruck. Another advantage is being able to detect potential mates, he says.

Dolphins commonly inspect each other’s genitals, including during courtship, which may provide an opportunity to sample each other’s urine, says Bruck.

We know they must taste each other’s urine rather than smell it because they don’t have functional smell systems, he says.

At this stage, bottlenose dolphins are the only known species that can identify familiar individuals based on taste alone. Other types of dolphins may do the same thing, but this will need to be explored in future research, says Bruck.

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