UNDERWATER AUDIOGRAM OF A TUCUXI (SOTALIA-FLUVIATILIS-GUIANENSIS)

Using a go/no go response paradigm, a tucuxi (Sotalia fluviatilis guia nensis) was trained to respond to pure-tone signals for an underwater hearing test. Auditory thresholds were obtained from 4 to 135 kHz. The audiogram curve shows that this Sotalia had an upper limit of hearing at 135 kHz; from 125 to 135 kHz sensitivity decreased by 475 dB/oct. This coincides with results from electrophysiological threshold measur ements. The range of best hearing (defined as 10 dB from maximum sensi tivity) was between 64 and 105 kHz. This range appears to be narrower and more restricted to higher frequencies in Sotalia fluviatilis guian ensis than in other odontocete species that had been tested before. Pe ak frequencies of echolocation pulses reported from free-ranging Sotal ia correspond with the range of most sensitive hearing of this test su bject. (C) 1998 Acoustical Society of America. [S0001-4966(98)03802-8] .