Bottlenose dolphins (Tursiops truncatus) moan as low in frequency as baleen whales.

Despite a vast number of investigations on the vocal repertoire of bottlenose dolphins, it is still not fully described. This publication reports on a newly discovered tonal low-frequency vocalization in the species at frequencies similar to baleen whale "moans." Dolphin moans are characterized by a slightly modulated fundamental frequency well below 500 Hz that ranges in duration from 0.2 to 8.7 s. Recordings (68 h) were obtained from eight Black Sea bottlenose dolphins residing in an open sea enclosure in Israel. Of 132 unambiguous moans, 49 occurred clearly associated with the release of air from a dolphin's blowhole, which allowed for identifying five moaning individuals. Reasons why this vocalization has not been previously described in any toothed whale are discussed. Moans might not be part of the species' natural repertoire but likewise might have been overlooked due to their inconspicuousness and scarcity, technical limitations, or methodological biases. The function of moaning is unclear; however, the data suggest that moans are signals of anticipating physical satiation provided by humans, i.e., feeding or petting. To further address these questions, verification of moans in other populations and experimental investigation of the properties of moan production and perception are required.