Abstract
Common bottlenose dolphins (Tursiops truncatus), produce a wide variety of vocal emissions for communication and echolocation, of which the pulsed repertoire has been the most difficult to categorize. Packets of high repetition, broadband pulses are still largely reported under a general designation of burst-pulses, and traditional attempts to classify these emissions rely mainly in their aural characteristics and in graphical aspects of spectrograms. Here, we present a quantitative analysis of pulsed signals emitted by wild bottlenose dolphins, in the Sado estuary, Portugal (2011–2014), and test the reliability of a traditional classification approach. Acoustic parameters (minimum frequency, maximum frequency, peak frequency, duration, repetition rate and inter-click-interval) were extracted from 930 pulsed signals, previously categorized using a traditional approach. Discriminant function analysis revealed a high reliability of the traditional classification approach (93.5% of pulsed signals were consistently assigned to their aurally based categories). According to the discriminant function analysis (Wilk’s Λ = 0.11, F3, 2.41 = 282.75, P < 0.001), repetition rate is the feature that best enables the discrimination of different pulsed signals (structure coefficient = 0.98). Classification using hierarchical cluster analysis led to a similar categorization pattern: two main signal types with distinct magnitudes of repetition rate were clustered into five groups. The pulsed signals, here described, present significant differences in their time-frequency features, especially repetition rate (P < 0.001), inter-click-interval (P < 0.001) and duration (P < 0.001). We document the occurrence of a distinct signal type–short burst-pulses, and highlight the existence of a diverse repertoire of pulsed vocalizations emitted in graded sequences. The use of quantitative analysis of pulsed signals is essential to improve classifications and to better assess the contexts of emission, geographic variation and the functional significance of pulsed signals.
Highlights
Tursiops truncatus, have a complex acoustic repertoire [1,2,3,4] comprised of three major types of signals: (i) tonal, omnidirectional, frequency-modulated whistles used as cohesion calls and communication signals [5,6,7], (ii) highly directional echolocation clicks used in biosonar tasks [8], and (iii) a variety of other pulsed signals, with high
Bottlenose dolphins in the Sado region, Portugal, produce a variety of broadband pulsed signals, comparable to the repertoire of other populations, that have been traditionally classified based on aural characteristics and graphical aspects [30]
Due to the singular characteristics of Short Burst-Pulses (S-BP) and their pattern of emission, we suggest that these burstpulses emitted in the Sado estuary may be a new/unreported signal in the acoustic repertoire of this species
Summary
Tursiops truncatus, have a complex acoustic repertoire [1,2,3,4] comprised of three major types of signals: (i) tonal, omnidirectional, frequency-modulated whistles used as cohesion calls and communication signals [5,6,7], (ii) highly directional echolocation clicks used in biosonar tasks [8], and (iii) a variety of other pulsed signals, with highPLOS ONE | DOI:10.1371/journal.pone.0157781 July 6, 2016Pulsed Signals of Bottlenose Dolphins collection in 2011, through the project 24052/4141/ 2010/RNES. Tursiops truncatus, have a complex acoustic repertoire [1,2,3,4] comprised of three major types of signals: (i) tonal, omnidirectional, frequency-modulated whistles used as cohesion calls and communication signals [5,6,7], (ii) highly directional echolocation clicks used in biosonar tasks [8], and (iii) a variety of other pulsed signals, with high. Pulsed Signals of Bottlenose Dolphins collection in 2011, through the project 24052/4141/ 2010/RNES. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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