Odontocetes produce communication sounds that are broadly categorized into pulsed calls and whistles, with variation ranging from intra-individual to interspecific levels. The diversity and complexity of these sounds often make categorization challenging. Investigating their functional roles, particularly in isolation contexts, can help clarify sound categories and reveal intra-individual and individual variation. Common bottlenose dolphins (Tursiops truncatus) have been reported to produce whistles in isolation context. In contrast, narrow-ridged finless porpoises (Neophocaena asiaeorientalis), considered non-whistling species, produce sequential pulsed calls (packet sounds) in isolation. Belugas (Delphinapterus leucas) and Pacific white-sided dolphins (Lagenorhynchus obliquidens), both capable of producing whistles, also emit pulsed sounds in isolation. These two species exchange pulsed sounds in a manner similar to whistle exchanges observed in bottlenose dolphins, whereas belugas do not exchange their whistles, suggesting inconsistent functions of whistles across species. A review of the predominance of pulsed sounds versus whistles suggests that pulsed sound communication may be evolutionary fundamental. Whistles may have subsequently adapted for group living and become the dominant sounds in certain delphinids, particularly in the subfamily Delphininae.
Tadamichi Morisaka (Wed,) studied this question.