Denise Herzing of the Wild Dolphin Project gives a SETI Institute lecture in which she discusses dolphin intelligence (and animal intelligence in general) and their communications abilities and what might be learned from them with respect to communicating with extraterrestrial intelligences:

The search for signals out of noise is a problem not only with radio signals from the sky but in the study of animal communication on Earth. Like SETI radio signal searches, dolphin sound analysis includes the detection, recognition, analysis, and interpretation of signals. Dolphins use three main types of acoustic signals and  many of these sounds have been a challenge to measure and categorize due to their graded and overlapping nature. The goal of this talk is to provide perspective from dolphin communication studies and lessons learned about signal detection and recognition.

And here is a video of a Google Hangout in which Herzing and Laurance Doyle and Gerry Harp  of the SETI Institute continue the discussion about dolphins and ETI: