The author received feedback that the “Sound” section of the article is too long and was asked to divide it into smaller subsections. Select all the possible subheadings the author should use to reflect the main topics covered under the heading “Sound.” (A) Birth (B) Coordination (C) Identification (D) Movements (E) Speed (F) Psychological Condition' In a crowd, a mother becomes separated from her young child. She calls to him, and he hears her and calls back. She moves toward the sound of his voice, and he moves toward hers. They continue to call back and forth, each moving toward the sound of the other's voice, until they are reunited. This might seem like an ordinary occurrence at any shopping mall or amusement park, except that this mother and child are not human, nor do they live on land. They are dolphins.

Dolphins, like humans, are social creatures, so communication plays a vital role in their existence. These marine mammals live and hunt in groups called pods, composed of fewer than ten to hundreds of individuals. The changing size and membership of these pods, and the complexity of the strategies of the hunt, require an intricate system of interaction. Scientists have not yet completely unlocked this system, but they have discovered quite a few secrets of dolphin communication. What they have learned suggests that these aquatic animals communicate in different ways for different purposes.

Sound

Dolphins communicate primarily through sound. Scientists believe this is because of the speed with which sound travels through water, making it a more efficient form of communication than other methods. The marine mammals use sound for multiple purposes, two of the most important of which are identification and coordination.

Dolphins are capable of producing a wide variety of noises, including clicks, whistles, squeaks, and barks. They can also mimic many different sounds, from the sounds of other dolphins to sounds made by boats and human beings. Of all these sounds, whistles are the most commonly used.

Every dolphin has a signature whistle, akin to a human name. In this way, the whistle serves as a method of identification. After a calf is born, its mother whistles to it constantly, until her whistle is imprinted on the baby's brain. Should the mother and calf become separated, they each whistle until they find each other again. Similarly, when an adult becomes separated from its pod, it whistles until it is reunited with its group. Dolphins also learn the whistles of others in their pod. When one dolphin wants to get the attention of another, it imitates the other animal's signature whistle.

Young dolphins swim together with adult dolphins in a pool
A calf, or young dolphin, recognizes its mother’s whistle.

Whistling also helps these marine mammals coordinate their pursuit of food. Dolphins emit their signature whistles to determine who is participating in the hunt. Then they employ different vocalizations to direct the action in capturing their prey. These sounds allow the animals to cooperate as they herd schools of fish and to take turns eating those fish in an orderly manner.

Scientists also believe that dolphins use sound to express their psychological condition. Louder sounds, such as a stronger signature whistle, may indicate that the animal is in distress. Distress can also be indicated by a series of squeaks. Similarly, dolphins in aggressive confrontations sometimes produce buzzing clicks.

Body Language

Sound, though important in dolphin communication, is not the sole method by which the marine mammals interact. They also make use of body language such as touch and movements of the head or tail. Scientists know far less about this means of communication than they do about the mammal's use of sound. While they have identified specific body movements and behaviors, scientists do not yet understand the meaning behind them.

Studies have catalogued movements such as eye rolls, head shaking, and playing dead. Researchers have witnessed dolphins holding fins and pushing, nuzzling, biting, and brushing against each other.

Scientists believe that some of these movements are meant to strengthen social bonds or show aggression, but they have not yet accumulated enough reliable data to state so conclusively or categorize the behaviors.

Conclusion

Despite the gaps in their knowledge of dolphin communication, researchers are certain about one point: dolphins do not have their own language. In other words, the marine mammals communicate, but they do not talk. This has not dampened hope for many, however, that someday humans might communicate directly with dolphins, or that dolphins might communicate directly with humans.