Dozens of dolphins have been recorded making specific whistle sounds that seem to refer to a shared meaning, expressing either questioning or alarm. Some researchers are claiming this shared usage is the best evidence yet that these intelligent marine mammals have a language-like communication system.
We know that dolphins make many 鈥渋nformation-carrying鈥� whistling noises, and may communicate extra detail by changing the volume of their whistles, but until now researchers have avoided claiming the animals 鈥� indeed, any other non-human animals 鈥� have a language.
Dolphin studies are particularly hamstrung because the animals鈥� marine environment makes it difficult to pinpoint a sound to a specific animal, says at the Woods Hole Oceanographic Institution in Massachusetts.
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So, Sayigh and her colleagues have been using data from the in Florida. For decades, the project has been identifying individual common bottlenose dolphins (Tursiops truncatus) using photographs of their markings and, since 2012, recording them with individually attached underwater microphones.
This has resulted in a vast pool of information on a community of about 170 wild dolphins in the waters around Sarasota Bay, spanning six generations and including individuals of all ages.
鈥淲e know all of these animals, we know their age, their sex, their entire lineages,鈥� says Sayigh. 鈥淲hen I do a playback with a certain animal, I know who鈥檚 its mum, who鈥檚 its sister and who it鈥檚 been hanging out with for the last few months.鈥�
Researchers have previously catalogued 鈥渟ignature鈥� whistles that seem like they are unique identifiers or names of dolphins that their podmates learn, but Sayigh and her colleagues are studying noises they call non-signature whistles.
They have so far identified 22 non-signature whistles made by multiple dolphins. The most widespread is produced by at least 35 different animals, followed by one shared by 25 dolphins. 鈥淭hose numbers keep climbing the more analysis I do,鈥� says Sayigh.
Sayigh and her colleagues speculate that the first call is a query used when dolphins see or hear something unexpected or unfamiliar. These whistles have a flat component and the team has mostly seen them made mostly by males. 鈥淭hey may make this whistle and they鈥檙e kind of like 鈥榃hat was that?鈥�,鈥� she says.
The second is a jarring whistle, reminiscent of alarm signals in other animals, and the dolphins seem to use it for the same warning purpose. To test this, the team played the sounds to six wild dolphins and found that five reacted negatively by moving away. This contrasts with a control test, in which 19 wild dolphins were played their own signature whistle; seven reacted negatively, a response rate less than half that of the alarm whistle.
Sayigh and her colleagues say these signals are the first evidence found in dolphins of a wider repertoire of shared, context-specific signals.
鈥淚鈥檝e actually spent most of my career arguing that there isn鈥檛 evidence for language-like communication in dolphins, but I do feel like a lot of the pieces are there in dolphins. Like the fact that they are flexible, lifelong vocal learners,鈥� says Sayigh. She鈥檚 comfortable with calling it a language-like communication system but says there is not yet enough evidence to say dolphins definitely have language.
鈥淚t鈥檚 really interesting to see that different individuals are producing whistles that are quite similar to one another,鈥� says at the University of St Andrews, UK. 鈥淚 definitely think they鈥檙e communicating, but at this point, I don鈥檛 think we could call it language.鈥�
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