Dolphins are considered to be the most intelligent mammals and researchers believe much of the dolphin's brain is used for communication or "echolocation".
While we still don't know if dolphins have a formal language, they do communicate with a "personal" whistle to identify themselves.
Unlike humans, dolphins do not have vocal cords, but they do use a complicated system of whistles, squeaks, moans, trills and clicks produced by their blow hole muscle.
Using echolocation, or sonar, dolphins send out frequencies by clicking. The returning sound waves are picked up by the dolphin's forehead and lower jaw and interpreted as to distance, size and shape of object.
This sound system is particularly useful at night as it allows the dolphin to navigate even if visibility is poor.
Dolphins have produced sound frequencies from 0.25 to 200 kHz, using the higher frequencies for echolocation and the lower frequencies for communication and orientation.
Do you want to learn more? Click on one of these:
The Dolphin Communication Project
What are dolphins?