Browsing by Author "dos Santos, Manuel E."
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- Aspectos acústicos do comportamento dos golfinhosPublication . dos Santos, Manuel E.Este artigo pretende apresentar uma recolha bibliográfica de alguns dados e hipóteses relativos a adaptações sensoriais e comunicativas dos cetáceos, particularmente dos golfinhos. São consideradas as suas capacidades perceptivas e as potencialidades dos canais de comunicação de que dispõem, sendo realçada a sua considerável especialização na utilização do canal acústico. Depois de uma breve referência às suas capacidades auditivas concretas e às teorias explicativa da produção de vocalizações pelos golfinhos, sistematiza-se uma classificação dos sons por eles produzidos. São descritas características acústicas das vocalizações, sendo também discutidas as suas possíveis funções e a sua combinação com outros tipos de sinais no decurso das interacções sociais. Enquanto os trens de impulsos curtos ou estalidos são usados sobretudo na ecolocação, os estalos e os assobios, bem como alguns sons não-vocais, assumem fundamentalmente funções comunicativas. São ainda referidas questões metodológicas relacionadas com o estudo acústico das vocalizações dos cetáceos, sendo comparadas as vantagens e as desvantagens do trabalho no meio natural e em situações de cativeiro. ------ ABSTRACT ------ This paper presents a literature review of some data and hipotheses on perceptual and communicative adaptations of cetaceans, particulary of dolphins. Their perceptive capabilities and the comparative possibilities of the communication channels available to them are discussed, and their considerable specialization in the use of the auditory channel is stressed. After a brief review of their specific auditory capabilities and a reference to the theories of sound production by dolphins, a classification of their sounds is presented. Some acoustical characteristics of their vocalizations are described, and their possible functions and combination with other of signals used in social interactions are discussed. While click trains are mainly used in echolocation, burst-pulses and whistles, as well as some non-vocal signals, have a predominant communicative function. A reference is also made to the methods used in the acoustical study of cetacean vocalizations, with a comparison of the pros and cons of recording in the wild or in captivity.
- A Quantitative analysis of pulsed signals emitted by Wild Bottlenose DolphinsPublication . Luís, Ana Rita; Couchinho, Miguel N.; dos Santos, Manuel E.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.
- Raise your pitch! Changes in the acoustic emissions of resident bottlenose dolphins in the proximity of vesselsPublication . Veiga Sobreira, Filipa; Luís, Ana R.; Alves, Inês S.; Couchinho, Miguel N.; dos Santos, Manuel E.Maritime traffic is a major contributor of anthropogenicdisturbance for cetaceans, especially for coastal populations,such as that of resident common bottlenose dolphins(Tursiops truncatus) in the Sado estuary (Portugal). Animalshave been found to adjust their vocal behavior by changingvocal rates, or call frequency and/or duration, to overcomemasking effects of underwater noise. To evaluate the poten-tial impacts of boat traffic on the acoustic behavior of thesedolphins, emission rates and acoustic characteristics of whis-tles and burst-pulsed signals were analyzed with and withoutboats operating nearby. In this study, no significant differ-ences were found for emission rates of each type of vocalelement in the presence of vessels. However, significant dif-ferences were found in acoustic parameters, namely changesin frequency and duration, for whistles and for pulsed sounds(creaks, grunts, squeaks, and gulps). These changes, such as ashift in vocal frequencies and production of shorter signals,may represent behavioral strategies to compensate for thenoisy environment. Although resident bottlenose dolphins inthe Sado region seem to have developed some tolerance tovessel noise, continuous noise exposure and noise-inducedfrequency shifts in vocal outputs could have indirect fitnesscosts for this population