Delving deep into unheard waters: new types of low frequency pulsed sounds described for the boto (Inia geoffrensis)

The Amazon river dolphin, or boto (Inia geoffrensis), is an endangered species, distributed over an extensive area of the Amazon-Orinoco basin. Here, we analyzed the acoustic behavior of a previously unstudied population of botos at the Juami-Japura Ecological Station, Amazonas. We categorized call types according to their visual and acoustical parameters. Random forest decision trees were used to assess the validity of our classification. Six types of narrowband pulsed sounds were found, of which four are being described for the first time for the species. The vocalizations analyzed had mean maximum frequency of 25.7 kHz and mean minimum frequency of 1.1 kHz. The narrowband pulsed sounds are complex and different from those emitted by most members of the family Delphinidae. Although the acoustic repertoire of botos is not completely understood in functional terms, these pulsed sounds may play an important role in the social structure of the animals.

Automated summary

The study analyzed the acoustic behavior of a previously unstudied population of Amazon river dolphins at the Juami-Japura Ecological Station, and identified six types of narrowband pulsed sounds, with four being described for the first time. These pulsed sounds, with high frequencies, may play an important role in the social structure of boto dolphins.