Acoustic characteristics of biosonar sounds of free-ranging botos (Inia geoffrensis) and tucuxis (Sotalia fluviatilis) in the Negro River, Amazon, Brazil

Abstract

Odontoceti emit broadband high-frequency clicks on echolocation for orientation or prey detection. In the Amazon Basin, two odontoceti species, boto (Amazon River dolphin, Inia geoffrensis) and tucuxi (Sotalia fluviatilis), live sympatrically. The acoustic characteristics of the echolocation clicks of free-ranging botos and tucuxis were measured with a hydrophone array consisting of a full-band and an acoustic event recorder (A-tag). The clicks of the two species were short-duration broadband signals. The apparent source level was 201 dB 1 μPa peak-to-peak at 1 m in the botos and 181 dB 1 μPa peak-to-peak at 1 m in the tucuxis, and the centroid frequency was 82.3 kHz in the botos and 93.1 kHz in the tucuxis. The high apparent source level and low centroid frequency are possibly due to the difference in body size or sound production organs, especially the nasal structure, the sound source of clicks in odontoceti.

The biosonar of the boto: evidence of differences among species of river dolphins (Iniaspp.) from the Amazon

“…Here, we found a mean peak frequency of 45.5 kHz for I. geoffrensis' clicks, as well as Kamminga & Wiersman (1981), that found I. geoffrensis' echolocation clicks at 40-80 kHz. However, our results showed peak frequency values dropping almost by half comparing to 96 kHz found by Ladegaard et al (2017) and 82 kHz by Yamamoto et al (2015). The river dolphin Sotalia fluviatilis (tucuxi), which overlaps its area of occurrence with I. geoffrensis, produces clicks with a peak frequency around 80-90 kHz (Kamminga et al, 1993;May-Collado & Wartzok, 2010).…”

“…Most of the studies on boto's clicks (e.g. Ladegaard et al, 2015Ladegaard et al, , 2017Yamamoto et al, 2015) describe only clicks recorded on the animal's body axis, unlike the present study, where we analyzed both on and off-axis clicks. On-axis clicks may not accurately represent the complete set of clicks that are acquired during passive acoustic monitoring of odontocetes (Soldevilla et al, 2008).…”

“…Vocalizing in lower frequencies can guarantee that the acoustic information is transmitted reliably, increasing the active space of the signal under conditions of greater attenuation and dispersion (Hamilton et al, 2001). Previous studies partly support this hypothesis that the peak frequency of Amazon river dolphin clicks that inhabited flooded forests was slightly lower compared to the Sotalia fluviatilis's clicks, species that does not go into the flooded forests of the Amazon (Yamamoto et al, 2015). Differences in the species and subspecies of the genus Inia…”

“…In the past few years, a greater effort has been made to understand the acoustic behavior of Amazon river dolphins (e.g. Caldwell, Caldwell & Evans, 1966;Kamminga et al, 1993;Ding, Würsig & Leatherwood, 2001;Podos, Da Silva & Rossi-Santos, 2002;Diazgranados & Trujillo, 2002;May-Collado & Wartzok, 2007;Yamamoto et al, 2015;Ladegaard et al, 2015Ladegaard et al, , 2017Amorim et al, 2016;Melo-Santos et al, 2019, 2020, but there are still no studies on the echolocation clicks of I. boliviensis and I. araguaiaensis. Most of the studies on boto's clicks (e.g.…”

Peer Review #2 of "The biosonar of the boto: evidence of differences among species of river dolphins (Inia spp.) from the Amazon (v0.2)"

“…Previous studies partly support this hypothesis that the peak frequency of Amazon river dolphin clicks that inhabited flooded forests was slightly lower compared to the Sotalia fluviatilis's clicks, species that does not go into the flooded forests of the Amazon (Yamamoto et al, 2015).…”