If you whistle at the cat or dog (or humans) when you return home, then you are giving a unique signature whistle as an introduction. Tursiops truncatus is the bottlenose dolphin. It whistles in captivity, but how these dolphins really use signature whistles has been intriguing scientists for a long time.
Vocal learning in whales, seals, bats and songbirds such as the nightingale are designed within sexual selection processes. Meaning of learned signals where individual calls are used has been discerned in both parrots and dolphins. Progress was made then on how these two species can use artificial signals that relate to their environment. The context of their use in bottlenose dolphins is the subject of a paper out today in the Proceedings of the Royal Society B: Biological Sciences.
In the depths of the sea mammal Research Unit of St Andrews University, Nicola J. Quick and Vincent M. Janik investigated whether the 50% of all whistles from bottlenose dolphins are signatures to be exchanged when they meet at sea.
Still in St Andrews Bay, during 2003/4, the Scottish east coast dolphin group were approached from a small boat and 17 whistle sections sampled. 15 of these were suitable, containing 156 individual whistles, lasting 170 minutes. 108 whistles were chosen for analysis. In many cases dolphin groups joined up after this exchange of signature whistles. Only 10% of "joins" would join without whistling . The whistling techniques involved only one dolphin from each group and the authors believe this has four connotations.
1. A lead animal makes the whistle.
2. Echo-location ensures that dolphins recognise each other, leaving the whistle as merely a part of a greeting ritual.
3. Separations that are short would not require individuals to ID their friends again.
4. Perhaps the groups are not too choosy about who they approach, although this is unlikely given the close sociability of many dolphins.
Dolphins can copy each others' whistles accurately, but this didn't confuse the issues in these specific instances. They use the copying technique in close individual interaction, yet to be fully investigated. Instead, in this study, signature whistle s were confirmed as passing between groups before a "join," but never between individuals in a group. Bottlenose dolphins are non-territorial, so the assumption would be that we have a counter-calling system that also keeps the individuals in primate groups close together. However, about 19 minutes had passed on average since any groups had been in previous contact, so the context in the dolphins is different.
Cognitive skills in dolphins would give a greater vocal learning capability than in non-human primates. The signature whistle could address a specific "person" in the group and the group organised either around one possible response or perhaps a less organised system whereby several possible answerers could reply! Next step: follow that dolphin and record everything it says!