Which dolphin species uses unique 'signature whistles' to identify individuals?

The dolphin species known for unique “signature whistles” that identify individuals is the bottlenose dolphin.

Each bottlenose dolphin develops a distinctive, learned whistle that functions much like an acoustic name. Other dolphins can recognize the whistle’s identity, and dolphins may copy another individual’s whistle to address that animal. The calls are frequency-modulated and are produced through the nasal passages and air sacs beneath the blowhole, not through human-like vocal cords.

Signature whistles usually develop during the first year of life. Calves learn from the sounds around them while shaping a whistle that remains individually distinctive. The sound can remain stable for many years, helping dolphins maintain social bonds, locate companions, coordinate group interactions, and keep mothers and calves in contact.

This does not mean bottlenose dolphins have a human-style spoken language. Their communication also includes burst-pulsed sounds, body movements, and echolocation clicks used to sense objects and prey. Research has found that dolphins can remember the signature whistles of former companions after more than 20 years, an unusually long social memory. Other dolphin species may use individually distinctive calls, but the evidence is especially well established for bottlenose dolphins.