Whistles of small groups of Sotalia fluviatilis during foraging behavior in southeastern Brazil

Abstract

Whistle emissions were recorded from small groups of marine tucuxi dolphins (Sotalia fluviatilis) in two beaches located in an important biological reserve in the Cananéia estuary (25 degrees 03'S, 47 degrees 58'W), southeastern Brazil. A total of 17 h of acoustic data was collected when dolphins were engaged in a specific feeding foraging activity. The amount of 3235 whistles was recorded and 40% (n=1294) were analyzed. Seven acoustic whistle parameters were determined: duration (ms), number of inflection points, start and end frequency (kHz), minimum and maximum frequency (kHz), and frequency range (kHz). Whistles with up to four inflection points were found. Whistles with no inflection points and rising frequency corresponded to 85% (n=1104) of all analyzed whistles. Whistle duration varied from 38 to 627 ms (mean=229.6+/-109.9 ms), with the start frequency varying between 1 and 16 kHz (mean=8.16+/-3.0 kHz) and the end frequency between 2 and 18 kHz (mean=14.35+/-3.0 kHz). The importance of this study requires an accurate measurement of the whistles' emissions in an unusual foraging feeding behavior situation on two beaches where several tucuxis, mostly mother-calf pairs, are frequently present. These two beaches are located in a federal and state environment Environmental Protected Area threatened by the progressive increase of tourism.

Whistle characteristics in free-ranging bottlenose dolphins (Tursiops truncatus) in the Mediterranean Sea: Influence of behaviour

“…Ten acoustic parameters measured from each selected whistle were dictated by its structure: duration (ms), start and end frequency (Hz), minimum and maximum frequency (Hz), frequency range (Hz), frequency at 1/4, 1/2 and 3/4 of duration (Hz), and number of inflection points. An inflection point is a change in the slope of the whistle contour from negative to positive, or vice versa (Pivari and Rosso, 2005). These whistle parameters were chosen both for consistency with previous acoustical studies (for example Erber and Simao, 2004;Bazúa-Durán, 2004;Morisaka et al, 2005;Pivari and Rosso, 2005;Azevedo et al, 2007;Baron et al, 2007), and because they could be easily measured manually from a spectrogram.…”

“…Secondly, throughout the entire study period, whistles were never recorded in presence of more than one group of bottlenose dolphins in the area. The inclusive definition of a dolphin focal group, to account for all individuals producing sound, was employed (Wang et al, 1995a(Wang et al, , 1995bErber and Simao, 2004;Bazúa-Durán, 2004;Morisaka et al, 2005;dos Santos et al, 2005;Boisseau, 2005;Pivari and Rosso, 2005;Azevedo et al, 2007;Baron et al, 2007;Quick and Janik, 2008) because during this study was not possible to ascertain which dolphin produced a whistle.…”

A characterization of Guyana dolphin (Sotalia guianensis) whistles from Costa Rica: The importance of broadband recording systems

“…The species occurs in bays, estuaries, river mouths, and shallow coastal waters along the western Atlantic Ocean from Southern Brazil to Northern Nicaragua, and possibly Honduras ͑da Silva and Best, 1996;Carr and Bonde, 2000;Edwards and Schnell, 2001;Flores, 2002͒. Despite the relatively broad distribution of the species most of what is known about its acoustic behavior and biology is from populations along the Brazilian coast from which echolocation clicks, pulsed sounds ͑e.g., calls and gargles͒, and whistles have been described ͑e.g., Wiersma, 1982;Terry, 1983;Monteiro-Filho and Monteiro, 2001;Azevedo and Simão, 2002;Erber and Simão, 2004;Azevedo and Van Sluys, 2005;Rossi-Santos and Podos, 2006͒. Whistles are the most studied sound type, and several whistle acoustic variables have been recently described from Brazilian populations ͑Monteiro-Filho and Monteiro, 2001; Azevedo and Simão, 2002;Erber and Simão, 2004;Azevedo and Van Sluys, 2005;Pivari and Rosso, 2005;Rossi-Santos and Podos, 2006͒. Monteiro-Filho and Monteiro ͑2001͒ first described Guyana dolphin whistles as low in frequency ͑up to 6 kHz͒ but a more extensive study revealed a much wider whistle frequency range ͑1.34-23.89 kHz͒ ͑Azevedo and Van Sluys, 2005͒.…”

The influence of seasonality, tide and time of activities on the behavior of Sotalia guianensis (Van Bénéden) (Cetacea, Delphinidae) in Pernambuco, Brazil

“…The negative correlation between the average number of estuarine dolphins and the pluviometric index may indicate that the sound of rain hitting the water could mask their whistles, making communication between these animals difficult, by comprising a similar sound frequency (GERSTEIN 2002, PIVARI & ROSSO 2005. When this takes place during foraging, estuarine dolphins move to deeper waters, where the sound of rain is not so strong.…”