Abstract:

A predisposition generally exists among delphinids for hearing high-frequency signals, raising the question: How much do dolphins actually use the ultrasonic range for social signaling? To answer this question, a low-budget, portable broadband recording system was developed to collect whistles and burst pulses from a population of Hawaiian spinner dolphins resident off the leeward coast of Oahu, Hawaii. This system employs a PCMCIA A/D converter to digitize signals directly into a laptop computer and has a maximum upper frequency limit of 140 kHz. Signals collected using this system reveal that spinner dolphins use the ultrasonic range extensively. Although the fundamental frequencies of whistles tend to be restricted below approximately 23 kHz, strong harmonics are often clearly visible up to 70 kHz. Even more high frequency in nature are the burst pulses. These signals often have little or no energy below 20 kHz and can extend beyond the recording limits of the system. Furthermore, high-frequency burst pulses are pervasive in the acoustic output of spinner dolphins, making it reasonable to assume that the ultrasonic range may, in fact, be important not only for echolocation, but also social signaling purposes.