Sperm whales don't just vary the rhythm of their clicks. They vary the clicks themselves, according to a new preprint.
The preprint, posted to arXiv and not yet peer reviewed, analyzed 1,483 recorded codas (the click sequences sperm whales use to communicate). Its authors found that individual clicks within a coda differ in spectral slope, bandwidth, and other waveform traits, not just in the timing between clicks. Those waveform differences carried information about which whale, or which social unit, was likely vocalizing, beyond anything timing data alone revealed. Looking at whole codas, the preprint also found that a coda's acoustic form predicts traits of the next coda, and the one after that, but a third coda back added no measurable signal.
That second finding is the more interesting one. Sperm whale codas have mostly been studied as isolated units, sorted into timing-based types. This preprint argues codas function more like short phrases with limited memory: context from two exchanges back still matters, three doesn't. That's a structural claim, not a claim about meaning. The preprint does not argue the whales are producing anything resembling syntax.
Call it acoustic texture, not vocabulary. It reads more like tone of voice than word choice, and like any single preprint, it needs replication before anyone rewrites the sperm whale communication textbook.