Sperm whales alter the rhythm and composition of their distinctive clicking sequences when ships approach, according to new findings that shed light on how these marine mammals respond to human-generated underwater sound.
The peer-reviewed work, drawn from more than 1,000 recorded codas produced by 15 identified whales, reveals systematic differences in coda structure in the presence of shipping noise. In waters off Dominica, researchers observed that intervals between clicks in certain patterns become shorter, effectively speeding up the sequences.
Whales also increase their use of specific vowel-like patterns known as A-vowels or aaaa codas when boat noise is present. One particular coda unique to the clan studied consists of five clicks in a 1-1-3 rhythm. Under ship noise this pattern accelerates as the intervals between clicks contract.
These acoustic adjustments are clear enough that vocalisations alone can predict the presence of nearby ships. The data came from acoustic tags attached to whales via drones, with shipping noise levels confirmed through digital geolocation records.
The observations add to earlier efforts by the same team to map the phonetic-like system within sperm whale communication. Project CETI, which applies machine learning, robotics and linguistics to the study of these codas, includes among its researchers David Gruber and linguistics lead Gašper Beguš from the University of California, Berkeley.