When you are driving and the gap with the car next to you narrows, a warning sound goes off right away. Whales might be similar. It turns out their songs change when ships are nearby. As the number of whales killed each year by collisions with ships increases, they may have devised a self-protective measure to warn companions that a ship is approaching.
Researchers with CETI (Cetacean Translation Initiative) found that in the ocean, sperm whales sing in a specific pattern when they hear ship noise. Sperm whales make click sounds like pressing a mouse button when a mother calls a calf or when a male and female look for mates. The point is that when a ship comes, they sing a click song that differs from usual. The findings were published on the 18th of last month in the international journal "Ecological Informatics."
◇ Sperm whale songs change when ships approach
The sperm whale is a large whale measuring 15 meters in length and weighing up to 50 tons. It is the largest among toothed whales, which bite prey with teeth like orcas and dolphins. Humans have long been fascinated by the songs of large whales such as sperm whales. Scientists call whale sounds "songs" because tones with particular pitch and rhythm repeat at length in a consistent pattern.
The CETI team led by David Gruber of the City University of New York tracked locations and recorded songs by attaching sensor and microphone devices to the backs of 15 sperm whales off the Dominican coast in the Caribbean over four years. They also recorded engine and propeller noise from nearby passing ships. At the same time, they used Automatic Identification System (AIS) data to confirm the actual routes of ships transiting the area.
The CETI researchers categorized sperm whale click songs into 21 types and called them codas. For example, the "1+1+3" coda involves click, click twice, pausing briefly, then clicking three times in a row. Although sperm whales have only 21 codas, changing rhythm and tempo or adding ornamentation increases the patterns to more than 300.
The team confirmed that the sperm whales around Dominica produced their group-specific 1+1+3 coda, but when ship noise was present in the background, the song speed increased noticeably. The intervals between clicks also shortened. In particular, when a ship passed, the proportion of the vowel a coda increased, and when there was no noise, the i coda appeared relatively more. Of course, calling them vowel codas does not mean sperm whales pronounce "ah" or "ee" like humans. The difference is in frequency.
Human vowels emphasize specific frequencies depending on the resonance structure of the mouth and throat. Likewise, sperm whale codas mix various frequencies from high to low, but a spectral peak appears where energy clusters in a specific frequency band. Among them, the a coda has one spectral peak, and the i coda has two.
◇ They may boost transmission or it could be a warning call
CETI is an international research project that uses artificial intelligence (AI) to decipher the meanings in whale songs. Gruber launched it in 2020 with a $33 million donation from a charity. The name mimics SETI, the Search for Extraterrestrial Intelligence.
Earlier, in 2024 the CETI team identified 21 codas corresponding to an alphabet in sperm whale songs, and in April they reported that the codas have vowel types a and i. This study can be seen as the start of a full-fledged analysis of the meanings of the songs.
Gruber said, "This study raises the question of whether the whales are talking about ships, or whether ships nearby are affecting their voice." In other words, sperm whales may detect ships and emit warning calls, or, as voices rise in noisy places, their songs may change to overcome ship noise.
U.S. Navy researchers previously reported in 2020 that minke whales increase volume in the presence of noise pollution. Orcas and humpbacks showed the same tendency. But the CETI team said sperm whales differ in that they change not just volume but also vocal speed and type. That makes it more likely to be a warning call.
Since the 19th century, sperm whales have been known as terrifying creatures that ram and sink ships. The protagonist of Herman Melville's 1851 novel "Moby-Dick" is a sperm whale. In fact, the American whaleship Essex, a 27-meter square-rigged whaler, was attacked and sunk by a sperm whale in the South Pacific on Nov. 20, 1820. It inspired "Moby-Dick."
Now, contrary to the novel, sperm whales are in danger. An estimated 20,000 whales worldwide die each year in ship strikes. With global maritime traffic expected to increase by at least 240% by 2050, whale-ship collisions are likely to grow more severe. Scientists have even deployed satellites to track whale migration routes and notify ships to alter course.
If it is found that sperm whales warn one another that ships are approaching, this could be used to prevent the growing number of whale-ship collisions. Until now, ships have been alerted to the presence of whales; in the future, whales might also be played warning sounds in their own songs to signal approaching ships. That would amount to a truly two-way collision warning system.
References
Ecological Informatics (2026), DOI: https://doi.org/10.1016/j.ecoinf.2026.103881
Proceedings B journal (2026), DOI: https://doi.org/10.1098/rspb.2025.2994
Nature Communications (2024), DOI: https://doi.org/10.1038/s41467-024-47221-8
Journal of the Acoustical Society of America (2020), DOI: https://doi.org/10.1121/10.0000596