The BBC have an article about Bottlenose and Guyana dolphins communicating with each other:
Bottlenose and Guyana dolphins, two distantly related species, often come together to socialise in waters off the coast of Costa Rica. Both species make unique sounds, but when they gather, they change the way they communicate, and begin using an intermediate language.
If they are anything like me, they will achieve this by continuing to speak English (or Bottlenose or Guyana) but slower and louder, perhaps adding a “ee” sound to every fourth or fifth word.
But all is not sweetness and light in the dolphin world. According to the article:
But often, the two species swim together in one group. These interactions are usually antagonistic, as the larger bottlenose dolphins harass the smaller Guyana dolphins.
The researcher quoted in the article, Dr Laura May-Collado of the University of Puerto Rico in San Juan goes on to speculate:
It is also unclear whether the two species are simply learning to communicate using a common language, or whether the Guyana dolphins alone are making the new sounds due to stress. It could even be that the Guyana dolphins are attempting “to emit threatening sounds in the language of the intruder”, in a bid to make the bottlenose dolphins desist, Dr May-Collado says.
Those of you of a more technical bent can find out more from the journal Ethology.