Browsing by Author "Couchinho, Miguel N."
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- Changes in the acoustic behavior of resident bottlenose dolphins near operating vesselsPublication . Luís, Ana Rita; Couchinho, Miguel N.; Santos, Manuel Eduardo dosPublished for the Society for Marine Mammalogy, Marine Mammal Science is a source of significant new findings on marine mammals resulting from original research on their form and function, evolution, systematics, physiology, biochemistry, behavior, population biology, life history, genetics, ecology and conservation. The journal features both original and review articles, notes, opinions and letters. It serves as a vital resource for anyone studying marine mammals.
- 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
- Signature whistles in wild bottlenose dolphins : long-term stability and emission ratesPublication . Luís, A. R.; Couchinho, Miguel N.; Santos, Manuel Eduardo dosWhistles are key elements in the acoustic repertoire of bottlenose dolphins. In this species, the frequency contours of whistles are used as individual signatures. Assessing the long-lasting stability of such stereotyped signals, and the abundant production of non-stereotyped whistles in the wild, is relevant to a more complete understanding of their biological function. Additionally, studying the effects of group size and activity patterns on whistle emission rate may provide insights into the use of these calls. In this study, we document the decades-long occurrence of whistles with stereotyped frequency contours in a population of wild bottlenose dolphins, resident in the region of the Sado estuary, Portugal. Confirmed stereotypy throughout more than 20 years, and positive identification using the signature identification (SIGID) criteria, suggests that the identified stereotyped whistles are in fact signature whistles. The potential roles of non-stereotyped whistles, which represent 68 % of all whistles recorded, are still unclear and should be further investigated. Emission rates were significantly higher during food-related events. Finally, our data show a comparatively high overall whistle production for this population, and no positive correlation between group size and emission rates, suggesting social or environmental restriction mechanisms in vocal production.