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In the sunlit shallows of Sarasota Bay, something extraordinary is unfolding. For over five decades, researchers have observed and recorded a resident community of bottlenose dolphins. Their goal has always been to better understand these intelligent marine mammals.
But now, one group of scientists may have taken a significant step forward – toward understanding how dolphins might speak to each other.
This step comes not through hopeful speculation but through data, audio analysis, and decades of patient fieldwork.
With support from institutions like the Woods Hole Oceanographic Institution (WHOI) and Brookfield Zoo Chicago’s Sarasota Dolphin Research Program (SDRP), a new frontier in dolphin communication has opened.
Laela Sayigh and her colleagues have uncovered striking patterns in dolphin whistles – sounds that may be more than random noise. They may hold meaning, even language-like qualities.
Studying dolphins for over 50 years
The dolphin population studied by Sayigh’s team is not anonymous. Researchers have tracked individual dolphins over decades, identifying them through physical markings and behavioral patterns.
This has allowed them to build one of the most comprehensive sound libraries in marine mammal research.
By using suction-cup hydrophones and digital acoustic tags (DTAGs), the team recorded dolphins under natural conditions during brief health assessments.
These methods yielded high-quality audio while maintaining the animals’ safety and well-being. Over 300 individual dolphins have been recorded this way, forming a unique archive of signature and non-signature whistles.
Several decades ago, signature whistles (SWs) were identified as unique, name-like vocalizations. They have long been the focus of research. But half of the whistles produced by Sarasota dolphins do not fall into this category.
These lesser-studied sounds, called non-signature whistles (NSWs), have become the new focal point for research.
Dolphins use shared whistles
The team identified 22 stereotyped NSW types. Two stood out for their frequency of use: NSWA and NSWB.
NSWA has been recorded from at least 25 dolphins, while NSWB has appeared in the vocalizations of more than 35 individuals. These whistles are not just common – they are repeated, shared, and distinct in structure.
“Bottlenose dolphins have long-fascinated animal communication researchers,” said Sayigh. “Without the over five-decade-long study by the Sarasota Dolphin Research Program, we would not have such an extensive library of vocalizations for individual dolphins.”
“With this, we can study non-signature whistles, which have received very little research attention to date. Our work shows that these whistles could potentially function like words, shared by multiple dolphins.”
This is not a casual observation. Playback experiments revealed something compelling: dolphins responded differently depending on the type of whistle played back.
NSWA often triggered avoidance, while NSWB provoked curiosity or query-type behavior. These are not random reactions – they suggest meaning.
How dolphins respond to different whistles
To test the whistles’ roles, the researchers conducted playback experiments in two settings. The first took place during brief catch-and-release health assessments. The second, more complex setup, involved free-swimming dolphins monitored by drones and tagged with DTAGs.
The playback protocol involved presenting two whistle examples, followed by a silence period. Whistles included signature whistles, SW copies (SWCs), NSWs, and unfamiliar sounds.
Researchers recorded behavioral responses such as turning, movement, or vocal mimicry. The orientation and motion data collected through accelerometers gave an additional dimension to the findings.
NSWA playbacks resulted in avoidance behaviors in most trials, suggesting an alarm function. NSWB, on the other hand, was linked to uncertain or inquisitive behavior. In some cases, dolphins even responded with a vocalization of their own – often NSWB itself.
In one notable trial, two allied male dolphins heard playbacks of their own whistles. Despite being together, they both responded by producing NSWB. This indicated the playback was unexpected and possibly confusing, prompting a query-like response.
Signs of social significance
A juvenile male once engaged in a 15-minute call-and-response session upon hearing his mother’s whistle played back. He mimicked all 148 stimuli with his own signature whistle.
This behavior points to the existence of intentional, structured vocal exchange. It wasn’t reflexive – it appeared thoughtful, even emotional.
In another case, dolphins copied a noisy NSW played during trials. These repeated interactions mimic elements of dialogue, implying these animals are not only hearing but replying in kind. This turns the idea of passive vocalization on its head and brings it closer to conversation.
The researchers noted that NSWB typically contains a constant frequency portion centered around 3kHz – a rare feature in Sarasota dolphin sounds. NSWA includes sharp upsweeps and downsweeps.
These features, while unusual, appeared consistently across multiple individuals, further strengthening the case for shared meaning.
Dolphin reactions depend on sound type
Early trials showed that high-volume playbacks caused dolphins to avoid the source.
The team then reduced the playback volume to match natural vocal levels. With this adjustment, dolphins still showed orientation shifts but were less likely to flee. This showed that it wasn’t just the sound’s volume, but its content, that shaped responses.
Control trials using a dolphin’s own signature whistle evoked mostly positive reactions. This reinforced previous findings that dolphins recognize their own names and respond to them in affiliative ways.
Meanwhile, other NSW types produced mixed responses, depending on context and individual identity.
Jeremy Coller, founder of the challenge, noted that humans share this planet with millions of other species, but for far too long we’ve only talked among ourselves.
“The Coller Dolittle Challenge aims to change that, so I’m excited by the fascinating work Laela and her team have done on dolphin communication. They are worthy winners and I can’t wait to see how they use AI to further interpret this vast set of data.”
Dolphins understand whistle meanings
This study provides the first concrete evidence that dolphins may use shared, learned, context-specific vocalizations that resemble elements of human language.
Like SWs, which serve as vocal labels for individuals, NSWs may represent objects, events, or intentions.
The variation in responses across individuals also points to complexity. Just as humans do not all react the same way to the same word, dolphins may interpret whistle meanings based on age, sex, mood, or social context.
In some cases, a group would approach a new subgroup after a playback. In others, individuals would turn away or stay put. Some responses suggest curiosity. Others hint at ambivalence.
The team hopes to refine their analysis further by incorporating new response categories such as “interest” and “ambivalent.” With more trials and deeper analysis, the functions of each whistle type may come into clearer focus.
Dolphins and their whistle language
The idea that dolphins use vocal labels for more than just identifying each other opens the door to a deeper understanding.
If non-signature whistles are learned and referential, as the data suggest, dolphins may possess a basic but real vocabulary. This is not language in the human sense – but it may not be far from it.
The study is far from over. Sayigh and her team continue to expand their whistle library and run playback experiments. They hope to map more of this vocal landscape and decode the nuances of dolphin interaction.
With each recording and each trial, researchers move closer to decoding a language that has echoed across the sea for millennia – only now are we beginning to hear it.
The study is published in the journal bioRxiv.
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