Sound travels 4.5 – 5 times faster through water than through the air. For this reason dolphins rely on sound for communication more than any other mode. Scientists believe that every bottlenose dolphin develops a distinctive high-pitched whistle, called a signature whistle (Tyack, 2000). This whistle appears to serve as a means of individual identification, much like a name. It may let the rest of the pod know which pod members are around, where they are, and, perhaps, something about their mental state. Dolphins in distress sometimes emit their signature whistles very loudly. Whistles may serve to establish or maintain vocal or physical contact between dolphins. Dolphins often respond to another dolphin’s whistle by whistling themselves or moving toward the whistler. If they become separated, a young calf and its mother whistle frequently until reunited. Dolphins also whistle when separated from other group members.