Evidence of sperm whale trumpets conveying individual and group context cues in a feeding ground

The sperm whale (Physeter macrocephalus) is a highly vocal marine mammal that spends most of its time foraging at depth. Although clicks comprise the large majority of their vocalizations, sperm whales also emit tonal sounds, such as trumpets, made up of multiple units. The function of these sounds remains a matter of debate. Here, we studied the acoustic structure of trumpets to provide new insights about the emitter features and the context of emission in the Balearic Archipelago, Western Mediterranean. Between 2018 and 2021, we collected data using a dual-element hydrophone towed from a sailing vessel. We photo-identified the individuals and acoustically estimated their lengths. Ten acoustic parameters were measured: four encompassing the entire trumpet, and six for each unit composing the sound. Over 27 hr of acoustic recordings and 111 encounters, we detected 46 trumpets, with trumpets occurring in 23% of encounters. A total of 21 individuals were photo-identified, and their mean lengths ranged from 10.78 to 12.76 m. Most of the trumpets occurred during Singleton or Multiple Singleton Encounters, which are typical of adult or sub-adult males. Furthermore, 46% of the recorded trumpets were combined with slow clicks, a long-range male vocalization. The fundamental frequencies of the trumpet were the most stable intra-individual parameters and showed a strong relation with the individual length. Conversely, the number and features of the units displayed greater variability, especially to the solitary vs non-solitary context. These results suggest that trumpet acoustic structure may encode information about the emitter’s characteristics based on their frequencies, as well as the social context, based on the parameters of the units that make up the trumpet. Our findings contribute to advancing the understanding of this understudied vocalization, even if further studies with a more extensive sample size are required to unveil the trumpet function.