32
(LFN sounds; Fig. 2.20). Moreover, authors demonstrated a greater amount of
sounds emitted, excluding the clicks, with lower frequencies during the day than the
night. Thus, the sound repertoire of the species is daylight dependent, with influence
on their social communication.
Another result of the study phase that began in 2011 was the observation of high
initial and minimum frequencies of Guiana dolphin whistles in the region compared
to previous studies for the species in Brazil. Deconto and Monteiro-Filho (2013)
recorded sounds with these parameters very close to those recorded in Costa Rica
(May-Collado and Wartzok 2009). Until then, the most accepted hypothesis was
that the frequencies of the Guiana dolphin whistles increased from higher latitudes
toward areas of lower latitudes (Azevedo and Van Sluys 2005; Rossi-Santos and
Podos 2006). Thus, reinforcing a hypothesis initially raised by Rossi-Santos and
Podos (2006), Deconto and Monteiro-Filho (2013) present new evidence that the
latitudinal variations reflect adaptations to the environment, a fact recently confirmed (Leão et al. 2015).
Continuing the acoustic study focusing on environmental influence on the spread
of Guiana dolphin sounds, IPeC researchers have conducted experiments in natural
environment both in the Northeast (Praia da Pipa) and in Southeastern Brazil
Fig. 2.18 A spectrogram highlighting the “noise” produced by a vessel equipped with an outboard
motor, represented by the green color horizontal band, which reaches up to 15 kHz
Note that whistles and clicks produced by Sotalia guianensis are masked by noise. Y axis represents frequency in kHz; X axis time in seconds
Fig. 2.17 Sounds produced by Sotalia guianensis and categorized by Monteiro-Filho and
Monteiro (2001). From left to right: whistles, screams, clicks, gargle. Y axis represents frequency
in kHz; X axis I time in seconds
E.L.A. Monteiro-Filho et al.
(LFN sounds; Fig. 2.20). Moreover, authors demonstrated a greater amount of
sounds emitted, excluding the clicks, with lower frequencies during the day than the
night. Thus, the sound repertoire of the species is daylight dependent, with influence
on their social communication.
Another result of the study phase that began in 2011 was the observation of high
initial and minimum frequencies of Guiana dolphin whistles in the region compared
to previous studies for the species in Brazil. Deconto and Monteiro-Filho (2013)
recorded sounds with these parameters very close to those recorded in Costa Rica
(May-Collado and Wartzok 2009). Until then, the most accepted hypothesis was
that the frequencies of the Guiana dolphin whistles increased from higher latitudes
toward areas of lower latitudes (Azevedo and Van Sluys 2005; Rossi-Santos and
Podos 2006). Thus, reinforcing a hypothesis initially raised by Rossi-Santos and
Podos (2006), Deconto and Monteiro-Filho (2013) present new evidence that the
latitudinal variations reflect adaptations to the environment, a fact recently confirmed (Leão et al. 2015).
Continuing the acoustic study focusing on environmental influence on the spread
of Guiana dolphin sounds, IPeC researchers have conducted experiments in natural
environment both in the Northeast (Praia da Pipa) and in Southeastern Brazil
Fig. 2.18 A spectrogram highlighting the “noise” produced by a vessel equipped with an outboard
motor, represented by the green color horizontal band, which reaches up to 15 kHz
Note that whistles and clicks produced by Sotalia guianensis are masked by noise. Y axis represents frequency in kHz; X axis time in seconds
Fig. 2.17 Sounds produced by Sotalia guianensis and categorized by Monteiro-Filho and
Monteiro (2001). From left to right: whistles, screams, clicks, gargle. Y axis represents frequency
in kHz; X axis I time in seconds
E.L.A. Monteiro-Filho et al.