Abstract:

Bottlenose dolphins’ phonations are commonly divided into three major categories: whistles, echolocation clicks, and burst pulses. Other categories are often mentioned and described as yelps, squawks, barks, and low-frequency narrowband sounds . Here, we report the occurrence of low-frequency tonal phonations with fundamental frequency within the 500–2000 Hz range, accompanied by numerous harmonics. Recordings were made using 48 and 192 kHz sampling rates and a 100 Hz high-pass filter in the presence of free-ranging bottlenose dolphins in Mississippi Sound, MS. Auditory sensitivity of the bottlenose dolphins has been studied extensively, and the results indicate that dolphins have their best hearing sensitivity in the higher-frequency range (15–110 kHz). Low-frequency sounds (above 75 Hz) can be detected as well, and it has been suggested that this detection mechanism may be entirely different from that used for higher frequencies and may even include mechanoreception. The occurrence of low-frequency phonations in wild dolphins indicates that low-frequency detection may play an important role in the animals’ everyday activities.