Researchers have discovered that sperm whales produce a distinct pattern of clicking noises when they hear the noise of boats, a finding so robust that scientists can now use it to predict when ships are nearby. The study, published in the journal Ecological Informatics, was conducted by Project Ceti, a non-profit research organization working to decode sperm whale communication.
Study Details and Findings
Over four years, researchers tuned into the calls of 15 sperm whales off the coast of Dominica in the Caribbean. They identified specific differences in the whales' "codas"—discrete patterns of clicks used for communication—when shipping was present. Individual click sequences became shorter, and one type of coda became more prominent than another.
Under normal conditions, recordings from a whale named "Atwood" captured a coda comprising five clicks in a 1-1-3 pattern (two clicks preceding three quicker ones), unique to this clan of sperm whales. With the background hum of a ship, Atwood issued the same rhythm but noticeably faster, reducing intervals between clicks.
"This research begs the question: are whales talking about the ships, or is it an impact on their voices because the ships are around?" said David Gruber, founder and CEO of Project Ceti. "And then if we’re able to discern what they’re saying about the ships, how might that impact policy and laws?"
Predicting Ship Presence from Vocalizations
The association was so strong that "in general, from their vocalisations alone, we can predict whether ships are around," said Gašper Beguš, linguistics lead at Project Ceti. For the study, Beguš and colleagues recorded more than 1,000 codas from the 15-strong sperm whale pod using audio tags attached by drones to minimize invasiveness. Background shipping noise was verified with digital geolocation data to confirm vessel proximity.
While several studies have shown marine animals increase vocalization volume in noisy conditions, the researchers were surprised not to see this trend in sperm whales. Instead, the creatures prioritized altering not just the speed but the types of codas they produced.
Vowel-Like Sounds and Their Meaning
This relates to previous Project Ceti research describing "use of vowels" in sperm whales. Communication among sperm whales has long been viewed as morse code-like clicks, but earlier work found that condensing gaps between clicks formed continuous sounds resembling two human vowels: "aaaa" and "iiii." In the latest research, the team identified differences in the prevalence of these vowel-like sounds in noisy conditions, with sperm whales using the "aaaa" coda more frequently.
"The study is actually one of the first glimpses that the vowels that we discovered might actually carry meaningful information. Because in the presence of shipping noise, they change the way they use those vowels," Beguš said.
Criticism and Expert Commentary
Some researchers have criticized Ceti's previous studies, finding fault with methods and saying that terms like "vowels" and "language" stretch associations between whale and human communication too far. Gruber says they address this by using terms such as "vowel-like" or "language-like."
Nathan Merchant, an underwater noise specialist at the UK government marine research agency Cefas, who was not involved in the research, noted that other unknown factors could drive the change in whale vocalizations aside from shipping noise. However, his "hunch" was that the relationship was causal. Merchant highlighted that a large body of work shows changes in behavior and call volume when marine animals encounter shipping noise. "Something that marks this study out is that it shows changes to the fine-scale content of those calls," he said. "It really adds another dimension of nuance to that story about how underwater noise can affect cetaceans."
He added that more research is needed to determine what these audible changes mean. "Are they [the whales] just struggling to say the same thing, or are they saying something different in the presence of this noise?" he said. "It’s a really intriguing question."
