Browsing by Author "Couchinho, Miguel Nogueira"
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- Brays and bits: Information theory applied to acoustic communication sequences of bottlenose dolphinsPublication . Luís, Ana Rita; Alves, Inês Sofia Carvalho Alves; Sobreira, Filipa Veiga; Couchinho, Miguel Nogueira; Santos, Manuel Eduardo dosAcoustic call sequences are important components of vocal repertoires for many animal species. Bottlenose dolphins (Tursiops truncatus) produce a wide variety of vocalizations, in different behavioural contexts, including some conspicuous vocal sequences – the ‘bray series’. The occurrence of brays is still insufficiently documented, contextually and geographically, and the specific functions of these multi-unit emissions are yet to be understood. Here, acoustic emissions produced by bottlenose dolphins in the Sado estuary, Portugal, were used to provide a structural characterization of the discrete elements that compose the bray series. Information theory techniques were applied to analyse bray sequences and explore the complexity of these calls. Log-frequency analysis, based on bout criterion interval, confirmed the bout structure of the bray series. A first-order Markov model revealed a distinct pattern of emission for the bray series’ elements, with uneven transitions between elements. The order in these sequential emissions was not random and consecutive decreases in higher order entropy values support the notion of a well-defined structure in the bray series. The key features of animal signal sequences here portrayed suggest the presence of relevant information content and highlight the complexity of the bottlenose dolphin’s acoustic repertoire.
- Monitoring underwater explosions in the habitat of resident bottlenose dolphinsPublication . Santos, Manuel Eduardo dos; Couchinho, Miguel Nogueira; Luís, Ana Rita; Gonçalves, Emanuel JoãoMaintenance work on the harbor of Setu´bal, in Portugal, required the removal of a 14-m deep rocky outcrop at the ship maneuver area, using about 35 kg of Gelamonite, a nitroglycerin-based highexplosive. This important harbor is located in the Sado estuary, a biologically rich environment and an important feeding area for a resident community of bottlenose dolphins. Using different safe range calculation models, a mitigation and monitoring plan was developed that minimized the risks of these underwater explosions for the dolphins. At our monitoring station, at 2 km from the demolition site, acoustic pressure levels in excess of 170 dB re 1 lPa (root-mean-square) were measured. Samples of dead fish collected at the site were indicative of shock trauma from the blasts.
- A Quantitative analysis of pulsed signals emitted by wild bottlenose dolphinsPublication . Luís, Ana Rita; Couchinho, Miguel Nogueira; Santos, Manuel Eduardo dosCommon 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.
- Whistles of bottlenose dolphins (Tursiops truncatus) in the Sado Estuary, Portugal: Characteristics, production rates, and long-term contour stabilityPublication . Santos, Manuel Eduardo dos; Louro, Sónia; Couchinho, Miguel Nogueira; Brito, Cristina MariaThis study focuses on the whistle characteristics and production patterns of bottlenose dolphins (Tursiops truncatus) resident in the Sado Estuary, Portugal. Recordings and observations were conducted inside the estuary and in adjacent coastal waters using single hydrophones between 1987 and 2000. In the groups sampled, the mean number of whistles emitted per minute per animal was 0.28. The acoustic characteristics of a sample of 735 whistles were measured and compared with data from other Tursiops populations, showing that, in a pattern of overall similarity, the whistles recorded in the Sado are relatively long and the frequency range used is relatively wide. Mean peak frequency was 9.2 kHz. About 30% of the whistles were stereotyped, and remarkable stability was found in several contours over a 12-year period. No relation was found between dolphin group size and whistle rate, suggesting some restriction in production; and no relation was found between dolphin group size and the emission of different contours. Significant variation was found between episodes of simple travel and more aroused activities in terms of the production of whistles in general and also of different whistle contours.