Signature of bottlenose dolphins whistles have just passed an important test in animal psychology. A new study by my colleagues and I has shown that these animals can use their whistles as name-like concepts.
By presenting urine and the sounds of distinctive whistles to dolphins, my colleagues Vincent Janik, Sam Walmsey and I recently showed that these whistles act as representations of the individuals who possess them, similar to human names. For behavioral biologists like us, this is an incredibly exciting result. It is the first time that this type of representative naming has been found in an animal other than humans.
The meaning of a name
When you hear your friend’s name, you probably imagine their face. Likewise, if you smell a friend’s perfume, that can also conjure up an image of the friend. This is because people create mental images of each other with more than one sense. All the different information from your senses associated with a person comes together to form a mental representation of that person – a name with a face, a smell, and many other sensory features.
In the first few months of their lives, dolphins make up their own specific identity calls – the so-called signature whistles. Dolphins often announce their location or greet other individuals in a pod by sending their own distinctive whistles. But researchers don’t know if, when a dolphin hears the distinctive whistle of a dolphin they are familiar with, they are actively imagining the calling person. My colleagues and I were interested in determining whether dolphin sounds are representative in the same way that human names evoke many thoughts of a person.
Dolphins use distinctive whistles to identify themselves.
No two signature whistles are alike.
Since dolphins cannot smell, they rely primarily on signature whistles to identify each other in the ocean. Dolphins can also copy the whistle of another dolphin to address each other.
My previous research showed that dolphins have great memories for each other’s whistles, but scientists claimed that a dolphin could hear a whistle, know it sounds familiar, but don’t remember whose whistle it belongs to. My colleagues and I wanted to determine whether dolphins could associate signature whistles with the specific owner of that whistle. This would address whether or not dolphins remember other dolphins and have them on their minds.
Urine as identification
The first thing my colleagues and I had to do was find another sense that dolphins use to identify each other. In the 1980s and 1990s, researchers studying spinner dolphins in Hawaii noticed that the dolphins occasionally swam with their mouths open through each other’s urine and feces. Using these observations as a springboard, my colleagues and I decided to test whether dolphins could recognize each other through urine.
We started by collecting urine from dolphins under managed care and simply pouring small amounts into lagoons where the dolphins live. The dolphins showed an immediate interest, and with little training, they quickly began following the research team when we carried sticks with cups filled with urine. When we poured urine into the water, the dolphins opened their mouths and swam through the plume of urine.
Our team then obtained urine from dolphins in other facilities to see if the subjects could distinguish between known and unknown urine. The dolphins spent more than twice as much time with their mouths open tasting known urine compared to unknown urine, providing the first evidence that dolphins can identify other individuals by taste.
With this, my colleagues and I had what we needed to test the representation in signature whistles.
Pairing urine and whistles
Previous studies in children have successfully used multiple senses to show that pre-linguistic infants can form conceptual representations of humans. My colleagues and I used this kind of work as a theoretical basis for our second experiment.
In our experiment, the team first led a dolphin to a speaker before pouring a small amount of urine into the water. After the dolphin tasted the urine, we quickly played the sound of another dolphin’s signature whistle. Sometimes that whistle would belong to the same person as the pee monster. Other times the urine and whistle did not match. The aim was to test whether the dolphins reacted differently if the urine and whistle were from the same dolphin than if the urine and whistle were from two different dolphins. If there was a consistent difference in how long the dolphins hovered close to the speaker in the matched or unmatched scenarios, it would indicate that the dolphins knew and recognized when a whistle and urine sample were from the same individual — in the same way a person would connect. can make a friend’s name to that friend’s favorite perfume
We found that when the urine and whistle matched, dolphins spent an average of about 30 seconds examining the speaker. When there was a mismatch, they only hung for about 20 seconds.
The fact that the dolphins consistently responded more strongly to matches than to mismatches indicates that they understand which whistles belong to which urine. This uses the same framework as other studies that use matching sensory information to show that animals have mental representations of individuals.
But what makes dolphins different is that they don’t just match physical traits — a face with a scent, for example. They do this with distinctive whistles that they invent themselves. Just as you can hear a name and imagine a face with all the associated memories, dolphins can hear a distinctive whistle and match the urine signal.
This work shows that dolphins have self-created cues that are representative, just as humans have made up names that are representative. Representation opens up the possibility that dolphins could theoretically make third dolphin references – where two dolphins communicating refer to a third dolphin that is not in the immediate vicinity. If dolphins can refer to dolphins that are not currently around them, it would be similar to the mental time travel a person makes when talking about a friend they haven’t seen in years.
Signature whistles represent the most language-like aspect of dolphin communication currently known. However, the scientific community knows little about dolphins’ non-signature calls or the functions of their other acoustic signals. With further research into how dolphins communicate with sound — as well as with chemicals — it may be possible to better understand the minds of these mammals.
This article was originally published on The conversation by means of Jason Bruck at Stephen F. Austin State University. Read the original article here.