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The bottlenose dolphin is a relatively robust dolphin with a short and stubby beak hence its name ‘bottleneck’. The dolphin is more flexible at its neck than other dolphins mainly because it vertebrae are not merged together like with the other dolphins. They have 18-26 pairs of sharp canonical teeth. Generally the color of bottlenose dolphins is light gray to slate gray on the upper part but pale to pinkish on the belly. An adult bottlenose dolphin weighs as much as 650 kg and its length ranges from 8-12 feet with males being significantly larger than females. Feeding behaviors among these dolphins vary widely. But in general, it involves capturing the prey usually as an individual although sometimes can happen as a coordinated group effort, feed in association with human fishing and even chase fish into mud banks and then feeding. They eat fish, crustaceans and squids. Adult bottlenose dolphins can consume 8-15 kg of food daily.
Males reach sexual maturity at around 10 years and females as earlier as 5 years. Gestation period is 1 year and calves are nursed for between 1-1.5 years and stay with their mother for 3-6 years before they are left on their own. Bottlenose dolphins are mostly distributed in temperate and tropical waters. They are however absent from Polar Regions with temperatures of below 45 degrees and below. They love inhabiting harbors, lagoons, estuaries, river mouths and bays. Research has shown that these dolphins live in open societies (American Cetacean Society Fact Sheet).
In the United States, the bottlenose dolphins are protected by the U.S. waters by the Marine Protection Act. Although there are direct and incidental exploitation of the bottlenose dolphins, the act has enabled a large number of the dolphins. These dolphins
Unlike many other animals, bottlenose dolphin’s brain is larger and scientists are still researching what aquatic adaptations require a big brain size. However, there is the hypothesis that a large brain size is a sign of intelligence.
Echolocation is defined as the use of sound and echoes by some animals to perceive their environment. Echolocation is therefore the ability that dolphins possess that enabling them to locate and discriminate surrounding objects. They do this by projecting high-frequency sound waves and then listen for echoes when the sound waves are reflected by objects.
Dolphins have the ability to emit high pitched series of clicks in a narrow beam just in front of them. When the clicking sound hits an object, say a fish, an echo is reflected back and the dolphin is able hear and accurately perceive the image of the object, and in this case the fish. Echolocation is the primary sense for dolphins and is a means of communicating too.
How echolocation works
The bottlenose dolphin has remarkable structures that help it to produce sound as well as detect echoes. A dolphin is able to produce click sounds by snapping their nostrils together. It uses a structure in its head called the sonic lips (like we humans produce sound using vocal chords). The sonic lips are what evolved from the dolphin’s nose and are tucked under the blowhole in the nasal cavity. A dolphin sends pressurized air past the sonic structures in a vibration mode producing click sounds. The dolphin’s head contains nasal sacs that allow air to be shuttled back and forth in the sonic lips. It is believed that the lips slap against fatty bodies in the dolphin’s nasal cavity thereby transferring the sounds through its head and out into the water. Dolphins have two sets of sonic lips allowing them to produce two sets of clicks simultaneously (Dolphin Communication Project).
The sounds produced travel through water, air or solid objects. Frequency is the number of vibrations per second and it is measure in hertz (Hz). Sounds that have higher frequencies are heard as higher tones and sounds with low frequencies as lower tones. Click sounds have a very short duration of between 40-70 microseconds but are known to be very loud. Bottlenose dolphins produce 220 decibels. These clicks contain high frequencies of up to 120 kHz which allow a dolphin to echolocate on very small details and objects and pick very fine details of the objects. High frequencies give better details allowing the dolphin to locate tiny species in the water (Dolphin Communication Project).
A dolphin’s click sounds are directed out of its head passing through some fatty tissue called the melon (the lump that is seen protruding out of its head). The melon has lipid called acoustic fat that has the same density as seawater. The dolphin is able to direct a beam of sound onto the object of interest. When the clicks hit the object of interest, an echo is produced directed towards the dolphin. The sound is received through its lower jaw and then transmitted towards the upper jaw into its middle. The dolphin then produces a kind of mental image of the objected in question. Research has shown that changes in the structure of the click echo is what a dolphin uses to form the mental image of the object but it is still not exactly understood how it manages to accomplish this (Dolphin Communication Project). The large proportion of the dolphin’s brain allows it to devote hearing and perception of sound. A dolphin’s echolocation is very sensitive and they are able to detect very small objects fifty feet away. The dolphin echolocate by emitting the clicks sweeping its head side to side and then pausing in between to the clicks to hear the echoes. The ‘vision’ is clear such that the dolphins can easily tell the object and even say if fish the type of fish and react accordingly (Claerr).
Through echolocation, dolphins are able to determine the size, shape, distance, direction and even the internal structure of the object. Echolocation enables the bottlenose dolphin to see in a clear and complex way. The acoustic signals play a key part in the life of dolphins. Light waves decay rapidly in water and therefore distant perception is only possibly by hearing and this is only solved by echolocation. Thus through echolocation, a dolphin is able to get food or escape danger (Dubrovsky, p.306-308). Evolution has seen the bottlenose dolphin abandon the auditory meatus and pinna and base on an ‘antenna’ next to each of the lower jaw. The form is important as it satisfies hydrodynamic streamlining while maintaining a good acoustic reception.
A bottlenose dolphin follows a neurological plan like other mammals. The dolphin employs a precision echolocation system that is analogous to the precision optical system like in other mammals whose job is to determine the range and direction of the object. The capability of the bottlenose dolphin to communicate with other animals is often comparable to that of humans. Vocalization for these dolphins cannot be comparable to any other species. This ability allows the bottlenose dolphins to hear and respond to acoustic signals. Researchers estimate that the dolphin can locate objects simultaneously within 10-20 cm out of 200m range. This capability is vital as it provides the velocity estimate for its target object usually between 2-50 km/h with a precision order of 2km/h. Researchers have analyzed the bottlenose dolphins auditory system and it suggests that the dolphin ‘sees’ in an acoustic range with the same fidelity as human; three dimensional in character achieved through with auditory neural circuitry. There is evidence that the dolphin has the ability to measure depths of its targets acoustically in a manner suggesting that they are translucent to the dolphin (Fulton).
Stan et al., 2008, argues that the ability of cetaceans to explore and interpret their world through echolocation is possible. Studies further show that bottlenose dolphins can relate very well to the information they receive from echolocation. Scientific results have indicated that bottlenose dolphins are able to relate visual and echoic representations of actions but they need some experience for such integration although they have not determined the duration of the experience yet (Stan et al.).
Signature Whistles in Bottlenose Dolphins
Bottlenose dolphins like other dolphins rely heavily on sound reception and production to navigate, hunt, avoid dangers and communicate inside waters.
Bottlenose dolphins identify themselves with signature whistles. Scientists have been able to identify the signature whistles (on a sonogram) especially because they are very distinct. The whistles in this case range at 7-15 kHz and lasts for a second or less. A mother dolphin will constantly whistle to her calf several days after giving birth. This is a special type of acoustic imprinting that will help the calf to learn to indentify its mother. The calf will then develop its signature whistle when about one month old. Bottlenose dolphins are also known to mimic each other’s signature whistles. This is still untested but scientists hypothesize that the dolphins use the whistles for social interaction with other dolphins. However, there is no evidence of a dolphin language (SeaWorld animals). Recent studies however suggest otherwise, bottlenose dolphins for the first time have been documented imitating one another’s signature whistles.
Marshall, 2011, asserts that subtle variations in whistles may suggest that calls are used as names. A team of UK researchers led by Stephanie King while monitoring a pair of 179 wild bottlenose dolphins in the coast Florida found out that some 10 pairs were copying each other’s signature whistles that they used to identify themselves to each other. This behavior has never been documented before and was seen only in a mother and her calf or a pairs of adults who move always together. King noted that copying was done after a couple gets separated implying that they were trying to get back together (Michael, Marshall). Research is still ongoing to determine whether the dolphins really do talk to each other or are just whistling.
Bottlenose dolphins belong to the species trunctus and are the most familiar. They are known to be very intelligent animals living in temperate and tropical parts of the world’s oceans. Dolphins are able to use echolocation to navigate, hunt, communicate and detect danger by clicking and listening to echoes. They do this by projecting high-frequency sound waves and then listen for echoes when the sound waves are reflected by objects. Echolocation is important as it enables dolphins to survive inside the waters and recent research points to the possibility that they can actually ‘talk’ to one another. More research need to be done to understand all that pertains to echolocation and seems that in the near future, more information will surface about these dolphins.