Dophins use whistles to say hello to each other

Photo: Terry Whittaker/ Solent 

Using hydrophones, the researchers made recordings of dolphins swimming in St. Andrews Bay, off the northeastern coast of Scotland, in the summers of 2003 and 2004. When groups of dolphins met up, they swapped whistles that outwardly sounded the same. But forensic analysis showed the whistles were in fact individual signatures, for they were never matched or copied by other dolphins. "Signature whistle exchanges are a significant part of a greeting sequence that allows dolphins to identify conspecifics [members of the same species] when encountering them in the wild,"
  says the study.