Le vocalizzazioni trumpet del capodoglio nelle Isole Baleari: analisi acustiche e contesto sociale.

The sperm whale (Physeter macrocephalus) is the largest of the Odontocetes species. The Mediterranean sperm whale population is considered genetically distinct and classified as “Endangered” on the basis of the IUCN Red List criteria. Therefore, it is important to better understand its behaviour and ecology in order to protect it. Since sperm whale spends most of its time foraging at depth, it is a species very suited to study through Passive Acoustic Monitoring. This study analyses sperm whale vocal behaviour, focusing on trumpets that are tonal sounds only occasionally documented, and thus less studied than other types of sperm whale sounds. The purpose of this project is to investigate the acoustic features of trumpet sounds and the social context in which they are emitted around the Balearic Islands. This area is one of the few in the Mediterranean Sea where females, calves as well as single males are regularly observed and it is very important because it is both a feeding and breeding ground for these animals. This project includes a comparison with one of the few studies about trumpets carried out in the Mediterranean Sea by Pace et al. (2021) with the aim of adding information on this vocalisation to better understand its function and to highlight possible differences. A total of 400 recordings were analysed over four years of data collection (from 2018 to 2021). Each recording was analysed with the bioacoustics software Raven Pro to detect trumpets and extrapolate the main acoustic parameters. A total of 46 trumpets were found. Additionally, a photo-identification effort was carried out in order to associate each recorded trumpet with the animal that emitted it. The software CABLE was employed to estimate the size of the sperm whales. Then a statistical analyses were carried out for the purpose of investigate the variation of the trumpets and units acoustics parameters in relation to social context variables during which this sound is emitted. The main results show that trumpets are emitted by sub-adult and adult male sperm whales at the beginning of a dive and they are often combined with other specific sounds used during echolocation or communication. Trumpets fundamental frequencies were statistically significant in relation to identified individuals and to the size, probably suggesting that they are characteristic of the animal. While, in units parameters there is a higher variability and they differ in relation to social factors. This might indicate that the information content may vary in the units within the trumpet. Moreover, both trumpets and units parameters seems to have a non-linear relationship with the time of the day. These new findings show a progress in the knowledge of this under studied sound and are in agreement with the previous studies.Even so, the exact trumpet function remains still unclear and further investigations are needed.