Signature whistle
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A signature whistle is a learned, individually distinctive whistle type in a bottlenose dolphin's (Tursiops truncatus) acoustic repertoire that gives the identity of the whistle owner.[1] The whistles are identified and studied in the wild or in captivity by researchers using hydrophones.[2] Vocal learning strongly influences the development of signature whistles,[3] which can remain stable for up to at least 12 years.[4] More often than not, calves develop signature whistles by the sounds they hear while making sure that they differ from close associates.[1] However, male calves tend to learn signature whistles that resemble their mother's.[1] They are believed to be most frequently used in the communication of captive bottlenose dolphins,[4] along with having specialized functions and properties.[5] Signature whistles are in a higher frequency range than humans can hear.[6] Researchers define a signature whistle as a whistle with a unique frequency curve that dominates in the repertoire of a dolphin.[7] Each dolphin has a distinct signature whistle that other members of its social group use to individually identify the whistler.[4] They are typically used for localisation purposes, however they also provide dolphins with behavioural context.[8][9] Signature whistles have an important role in facilitating mother–calf contact,[6] group cohesion and social interaction.[3]