Bottle nosed dolphins communicate by a series of whistles and clicks, and though experts are unsure of how complex this communication is, individual dolphins can definitely recognise and respond to each other. Like all dolphins, they use echolocation to form a 'picture' of their surroundings in murky water. They emit a series of loud clicks which travel through the water - if the sound hits a solid object, an echo is bounced off it and returns to the dolphin, which is then able to interpret the sounds into a map of its surrounding environment.
They also have their very own series of whistling noises that they use to identify themselves. Every dolphin has a unique sound, almost like a name. It appears that they are able to recognise and remember individuals that they meet, even having been separated for many years. Different groups of dolphins also develop their own community 'songs' and teach them to new generations.
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