By Andrew Crowder and Kristi Miller

"There is something about porpoises that makes human beings turn not quite rational. It has something to do with a sea-land link, an animal-man link, an extraterrestrial-earth link--some connection to another world beyond our own. These friendly, smiling mammals seem to represent everything good about life on this planet" (Hauser 44).

Dolphins use a series of different vocalizations in their daily activities. What are dolphin sounds for? They are used for identification, echolocation, and a weapon. There are common sounds: whistles and squeals and there are pulse sounds used for "seeing" inside objects and prey. Also, very high pitched sounds can be used to stun and confuse prey during foraging to make them easily caught. Sound travel in water is much different than in air because of the denser medium and dolphins have evolved many means to utilize their resources to thrive.

Bottle-nosed dolphins, characterized by a "built in smile" formed by the curvature of its mouth, are small, streamlined whales with a well-defined beaklike snout. Popularly noted for grace, intelligence, playfulness, and friendliness to man, the bottlenose has become the most widely known species of all marine mammals. Bottlenose dolphins are gray to gray green or brown in color on the top and white or white pink on the bottom with smooth skin. This is called countershading and is a means of protection. Dolphins measure up to 3.7 m. (12 ft.) in length and can weigh 454 kg. [(1000 lb.) SeaWorld]. They are a gregarious mammal often living in groups of a few to several hundred and feed mainly on fish. The bottlenose dolphin has few enemies in the sea. Tiger sharks, dusky sharks, bull sharks, and occasionally killer whales attack dolphins for food. However, their biggest threat is man. Fishers have used dolphins for years to spot tuna and other commercial fish, unfortunately killing many in the process. Those that are caught in their nets eventually drown to death because they are mammals and breath air. Commercially, dolphins are taken for meat, leather, oil, and meal products for animal feed and fertilizer.

Dolphins use a variety of vocal and nonvocal signals in combination. Whistles are one of the sounds they use as a contact call to identify the sender to the rest of the group, attract mates, and in murky waters, especially, give its location. These whistles play a central role in dolphin-to-dolphin communication. Each individual dolphin has its own unique whistle called a "signature whistle." The purpose of the whistles are to identify the dolphin vocalizing, give its location, and convey information of the situation to the rest of the group. They are very useful as a contact call from mother to infant. If mom and her offspring get separated they will emit a particular call back and forth to each other until they are reunited.

Calves develop signature whistles anywhere between two months and one year old. They will remain unchanged for at least twelve years and quite likely will last for their entire life span. (12 years is the longest any documented study, so far, has been underway). Interestingly, female offspring have whistles that vary greatly from those of their mothers and male offsprings’ whistles closely match their mothers’. This is probably because females will remain within their mother’s band when they reach adulthood and require a signature whistle very different to hers for identification. On the other hand, male dolphins leave their mothers to join a bachelor group with other young males and it wouldn’t be a problem to have a similar whistle because they may never cross paths again.

These whistles, squeaks, moans, trills, and clicks are produced by sphincter muscles within the blow hole because dolphins lack vocal cords (http://www.beach-net.com.). Signature whistles last about one second and vocalization may last one minute without repetition. They will vary according to activity and feelings at that specific time. Acoustic pictures or sonograms provide data on the whistles. The structure of their contours is what differentiates the different sound production. They show that they keep the same general configuration but may change in pitch or duration. Emotions are expressed differently for each individual. Although they do not use words, the way they broadcast their signature whistle conveys messages of mood: happiness, danger, and worry to the others. "Just as one human stews in silence when angry while another screams and shouts, one dolphin may produce a short, high-frequency version of its whistle when distressed, while another produces a long, low-frequency version under the same conditions" (Shane 42). Stressful situations are often expressed by pulse squeaks and aggressive confrontations are buzzing click trains. In general, vocalization is heard most often when a group changes their direction or activity.

When swimming together at least 50% of all the sounds they produce are signature whistle and with captive dolphins as much as 90% are signature whistles. Often times captives will imitate the whistles of other tank members. This may be a way one the dolphin says, "Hey pal it’s me over here." In one study of seven captive animals, six of them were producing similar and particular whistles that were unfamiliar to observers. One researcher while reviewing audio tapes discovered the particular whistle was the signature whistle of a tank mate who had died a year earlier. Dolphins often respond to a whistle by either whistling themselves or by moving towards the whistler.

Another vocal sound a dolphin produces is pulse sounds or clicks. These clicks are repeated at different rates and frequencies and are used to probe the world around them the same way a submarine uses sonar or a bat sees in the dark. They are used for orientation and navigation and are extremely important at night and in murky waters. These sounds range from 0.25–200 kHz, but normal high sounds range from 150-160 kHz. In echolocating, the dolphin produces short broad-spectrum burst pulses that sound to us like clicks (http://www.umassd.edu/Public). These clicks are reflected from prey or any other object of interest and provide the dolphin with information about it such as size, shape, and even density. It is a sort of 3-D location device. The clicks are generated in its nasal sacs, called diverticula, which are located below the blow hole and behind a fatty substance in the front of the melon (http://www.mtn.co.za). The melon acts like a lens in focusing the sound into a narrow beam that is then projected out in front of the dolphin. The sound travels forward and strikes the prey, and is then reflected back towards the animal who receives the returning energy echo in its lower jaw and eventually its inner ear. The time lapse between the clicks and the echo enables the dolphin to determine distance. The closer the object and dolphin are the quicker the clicks get. A foraging dolphin would use a 7 kHz ping, therefore giving more information. Lower frequencies travel farther but higher frequencies give more detail, such as if an animal has a swim bladder or not. Dolphins are even able to distinguish between different species of fish by echolocation. In a way they can "see" inside one another’s bodies using their natural ultra-sound. They have also been know to use their high pitched sounds as a weapon. By sending out sounds up to 230 decibels the dolphins frighten, stun, and confuse prey making them easier targets.

Echolocation does have its disadvantages though it lets the dolphin’s prey know where they are, and can not pick up "invisible" objects, such as a jellyfish or an item floating on the sea surface because of the medium change into the air.

In conclusion, while dolphins can communicate visually, chemically, and through touch, they rely most heavily on auditory signals. It is not known if dolphins have a formal language, they do communicate with a signature whistle that identifies themselves. In addition, there are two other types of vocalization used by dolphins. Pulse sounds are used for echolocation, and extremely high frequency sounds are use for foraging and hunting down prey. Together they can put together an extremely efficient and complicated sensory system which enables them to effectively survive in this dense medium.

Physician John C. Lilly, who specialized in brain research, made a prediction in 1961, "[The dolphins] are here waiting for us to grow up and maturely communicate..." (Chollar, "Man" 56). Perhaps Lilly was correct in his prediction. Dr. Diana Reiss, director at Project Circe, a study of dolphin communication and behavior, and the "lady who talks to the animals" says, "We humans need to understand more about our own capacity as a species before speculating about other species" (Hartwell 63). We focus on teaching them how to understand us. Maybe we need to let them teach us how to interpret their language and world.

Chollar, Susan. "Conversation With the Dolphins." Psychology Today Apr. 1989: 52-56.

Chollar, Susan. "The Man Who Talked to Dolphins." Psychology Today Apr. 1989: 56.

Hartwell, George. "Dolphin Talk." Oceans Mar-Apr. 1987: 62-63.

Hauser Hillary. "Playing With the Porpoises and Dancing With the Dolphins." Oceans Nov. 1984: 43-45.

SeaWorld Busch Gardens, Animal Resources. SeaWorld Inc., 1996. Online. Internet. 1997. Available: http://www.bev.net/education/SeaWorld/bottlenose_dolphin/html

http://www.beach-net.com/dolphins/communication

http://www.mtn.co.za/whaleroute/echolocation

http://www.umassd.edu/Public/People/KAmaral/Thesis/echolocation

Shane, Susan H. "Smarts: Notes On Dolphin Brain Power, Communication, Skills, and Social Style." Sea Frontiers Mar-Apr. 1991: 37-43.

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