Marine mammals establish or maintain contact with specific individuals using short-range vocalizations. The most striking example of marine mammals using sound to make or maintain contact is between mother and offspring. It is very important for a mother to remain in close communication with her offspring for feeding and protection from predators.
Dolphin societies need a highly developed communication system because group numbers and members are constantly changing. Bottlenose dolphin use whistles to maintain contact between mom and calf, as well as between individuals in a group. Whistles are tonal sounds that change in frequency over time. Each bottlenose dolphin has its own unique whistle. This is referred to as its signature whistle, and it is used to broadcast the identity and location of the animal that produced it. The spectrogram below shows a dolphin whistle containing three sound loops. The unique feature of each dolphin's signature whistle is the loop shape. The number of loops from the same dolphin may change from whistle to whistle, but the unique loop shape remains the same. The dolphin whistle below has a frequency of 7-23 kHz.
Click either choice below to hear the bottlenose dolphin:
Sound clip provided by Jennifer L. Miksis Olds. Released under Creative Commons License, non-commercial - no derivs.
The whistle sounds like a chirp repeated three times. Listen to the whistle while looking at the spectrogram. Can you hear the three separate loops?
Sperm whale produce rhythmic patterns of clicks when they are resting or socializing at the surface. These clicks are much shorter than dolphin whistles and have a much broader frequency. They sound very similar to a loud human handclap. The click patterns are called codas, and it is thought that each sperm whale has its own individually distinctive coda pattern. It is common to hear whales exchange codas during social behaviors.
Sound courtesy of WhaleAcoustics, LLC.
Seals and sea lions that breed in colonies have also developed a form of communication that uses individually distinctive vocalizations to reunite mom and pup when the moms return to the crowded colony after feeding. A mother will give a pup-attraction call when she returns. Her calls are heard by her pup and are often returned with calls from the pup. Both mother and pup recognize each other's vocalizations, which allow them to find each other in a very crowded rookery.