Preliminary analysis on the emission contexts of the bray-call sequences of the Mediterranean common bottlenose dolphin

The common bottlenose dolphin (Tursiops truncatus, BD) can produce distinctive sequences composed of multi-unit rhythmic signals at low frequency and short duration, known as the Bray-Call series (BC). BCs have been mainly recorded during feeding activities, but little is known about their possible communicative function in social contexts. The BD population inhabiting the Tiber River estuary (Central Tyrrhenian Sea, Rome) exhibits a complex repertoire of BCs, composed of 13 distinct types of single- and multi-element sequences made up of different arrangements of 3 main sounds (i.e. Gulp, Grunt, and Squeak.) Here, the context of emission of these sequences identified from recordings collected between 2017 and 2020 is investigated, to gain insight on their usage. To highlight potential differences in the amount of sequences emitted in feeding and social behavioral states, the Emission Rates (ER=n. sequences/minute) were compared through Mann-Whitney test. To address the influence of behavior on BCs diversity, a GLM Poisson was fitted assuming the total types of sequence as the response variable and behavioural states as predictor variables. Results showed that ER varies significantly in the two contexts (W=4831.5, p<0.001), with higher values during socializing. A significant diversity in the type of sequences emitted during feeding and socializing emerged as well (z=3.298, estimate=0.61587, p<0.001), with all 13 types used in social context only. A single-element sequence, composed of Gulp repeated in series, appeared to be the most emitted in both contexts. These results suggest a strong relation between BCs production and sociality, opening up the new scenario that the use of these sequences is not limited to foraging, and supporting the hypothesis of a communicative function in both contexts. Unrevealing the role of BCs may facilitate behavioural and habitat use studies through passive acoustic monitoring and may reveal possible alterations of communicative processes by anthropogenic and ecological factors.