Dolphins Label Their Friends With Names
Dolphins recognize familiar individuals, independent of sensory modality.
Posted May 18, 2022 | Reviewed by Gary Drevitch
- Dolphins can recognize other dolphins they know from the taste of their urine alone and from the sound of their signature whistle.
- A new study shows dolphins can integrate cues from acoustic and taste modalities to form an independent, labeled concept for known individuals.
- The results suggest dolphins’ signature whistles may function as representational labels, like human names.
It’s been nearly 60 years since scientists first described dolphins’ use of signature whistles. These are individually distinctive whistles used by dolphins to broadcast their identity, leading some to compare them with human names.
Studies of captive dolphins offer intriguing support for this idea. Research has shown that dolphins are responsive to the signature whistles of dolphins they know. What’s more, they can use other dolphins’ whistles to address individuals and remember these whistles for 20 years or more.
However, it was not known whether dolphins could use signature whistles the way that humans use names; that is, as a representational label (a call that can stand in for an object the way a noun can in our language).
“For example, if I say your best friend’s name, you will picture that individual in your head,” says Jason Bruck, a biologist at Stephen F. Austin State University. “Do dolphins do the same thing? If they do, that means signature whistles can function as representational labels the same way human names do.”
A Taste of the Familiar
To investigate whether dolphins use labels like we do, Bruck, along with Sam Walmsley and Vincent Janik of the University of St Andrews, conducted what’s known as a cross-modal study. In this kind of study, a subject is asked to identify an object or individual across different sensory modalities.
“It’s the same thing as a person seeing a mug and calling it a mug versus touching it blindfolded and still calling it a mug,” says Bruck. “And while this might sound like an easy task for a human, animals don’t always do this in their native communication systems.”
In the new study, the researchers tested eight captive bottlenose dolphins across their senses of hearing and taste. Based on dolphin behavior and biology, they hypothesized that the animals might acquire identity information from tasting compounds in other dolphins’ urine, in addition to hearing their signature whistles.
First, Bruck and his colleagues presented dolphins with urine samples (delivered to their enclosures via a cup on a long pole) from familiar and unfamiliar dolphins. They found that dolphins spent about three times as long sampling urine from familiar individuals compared with urine from strangers. A similar preference for familiar over unfamiliar has been previously reported for signature whistles.
Next, the researchers paired urine presentations with acoustic playback of signature whistles from underwater speakers. The whistle was either from the same dolphin that provided the urine sample (a match) or a mismatched dolphin. They found that dolphins responded more, by spending longer investigating the playback speaker area, to matches than mismatches. That the dolphins responded similarly across the senses, in matched and mismatched scenarios, indicates they can correctly assign whistles to the whistlers, says Bruck.
The findings mark the first case of social recognition by taste alone in a vertebrate animal (dolphins cannot smell as most other vertebrates can).
Bruck and his colleagues say it is likely that dolphins can also infer other information from urine, such as reproductive state, but we are just beginning to understand urine signaling in these animals. For instance, little is known about how chemical pollution might impact dolphin social communication in the wild, says Bruck.
“We may find that oil spills, the chemicals we use to disperse oil, chemical run-off, and other human effects may impede dolphins’ natural ability to chemically signal to one another,” he says. “This might prevent males from identifying reproductively capable females or diminish dolphins’ abilities to recognize individuals.”
Overall, Bruck and his colleagues say their results demonstrate that dolphins can integrate identity information from acoustic and taste stimuli to form an independent, labeled concept for known individuals. In other words, dolphins can label their friends in their minds and think of these individuals as more than the stimuli they use to recognize them.
“This means that each time a dolphin produces the whistle of another group mate or a dolphin responds to a whistle of a former group mate it hasn’t seen in years, it is likely that they are producing or responding to those whistles with full understanding of the individual those whistles represent,” says Bruck. “Dolphins could very well be capable of making third-dolphin references, referring to dolphins in absentia.”
If dolphins have these representations of other dolphins, they may be capable of cognitive feats such as planning, mental time travel, or simulating social scenarios.
“It also raises the possibility that signature whistles may be convergent cognitively with our use of names in that signature whistles, like human names, are learned and innovated signals, independent of the voice recognition systems found in many other animals,” says Bruck.
“It is not every day that scientists find evidence of ‘noun’-like use of signals in a non-human vocal system. That’s pretty exciting.”
Bruck JN, Walmsley SF, and Janik VM. 2022. Cross-modal perception of identity by sound and taste in bottlenose dolphins. Science Advances 8: eabm7684. Doi: 10.1126/sciadv.abm7684.