(CN) — Scientists have not yet decoded what sperm whales are saying to each other, but a study published Tuesday in Nature Communications shows their language is more complex than previously believed.
Researchers already knew that sperm whales communicate through "codas" — bursts of clicks that are about two seconds long. Codas are considered the basic unit of sperm whale communication, comparable to words.
Praytusha Sharma and colleagues from Project CETI, an international initiative aimed at understanding sperm whale communications, analyzed data from the The Dominica Sperm Whale Project, which includes 8719 codas recorded between 2005 through 2018, documenting the tempo and rhythm of the clicks made by a group of sperm whales in the Caribbean. The recordings exhibit 21 previously identified coda "types."
If codas are the equivalent of words, a language with just 21 words doesn't imply complex communication. But sperm whales display complex social behavior and group decision-making, which made scientists suspect there was more going on than a cursory glance at the data would suggest.
The study authors suggest prior research only focused on codas in isolation — a limiting approach, since these codas are often produced as part of larger sequences. Sometimes, codas are made by whales taking turns with each other; in other instances, groups of whales have been known to create multiple codas at once, in what is referred to as a "whale chorus."
With this in mind, the scientists took a wider look at how sperm whales communicate with each other, considering each code within the context of full exchanges between whales. As a result, they developed an "exchange plot," which illustrates two newly discovered features of sperm whale communication: "rubato" and "ornamentation."
"Rubato" is a change in the duration of codas, which appears to vary over the course of an exchange. This variation isn't random — instead, it increases and decreases according to a smooth pattern that is imitated by other whales involved in a whale chorus.
"Ornamentation" is the inclusion of additional clicks at the end of a coda.
"We hypothesized that ‘extra’ clicks play a different role from the other clicks in the codas in which they appear: they do not determine discrete coda type," the study authors write. "Instead, like rubato, they constitute an independent feature of the sperm whale vocalisation system."
The authors say these elements combine with the tempo and rhythm of the codas to create "a more complex sperm whale communication system with a greater information-carrying capacity than previously reported."
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