King and her colleagues collected acoustic data from wild bottlenose dolphins around Sarasota Bay, Fla., from 1984 to 2009. The researchers also intensely studied four captive adult male dolphins housed at The Seas Aquarium, also in Florida.
The captive males are adults that keepers named Calvin, Khyber, Malabar and Ranier.
These bottlenose dolphins, however, as well as all of the wild ones, developed their own signature whistles that serve as names in interactions with other dolphins.
"A dolphin emits its signature whistle to broadcast its identity and announce its presence, allowing animals to identify one another over large distances and for animals to recognize one another and to join up with each other," King explained. "Dolphin whistles can be detected up to 20 km away (12.4 miles) depending on water depth and whistle frequency."
The researchers said dolphins copy the signature whistles of loved ones, such as a mother or close male buddy, when the two are apart. These "names" were never emitted in aggressive or antagonistic situations and were only directed toward loved ones.