Dolphins have evolved complex sensory functions which they use as a form of echolocation. In this article we look at how they manage to do this.
Dolphins use internal sounds which they beam out into the water using fat deposits to locate and identify objects around them.
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Why Do Dolphins Use Echolocation?
Due to the evolutionary history of dolphins, unlike other large fish such as sharks, dolphins did not have the perfect senses to survive in the oceans. Whereas sharks had a well-developed sense of smell and could locate their prey using this, the early whales which originated on land did not.
To get over the problem of sharks attacking them, non-toothed whales evolved into enormous animals. By eating krill and not competing for the same food as sharks, this enabled them to survive against the sharks, allowing them to evolve into larger animals.
Dolphins, along with toothed whales, had to develop a new sense to combat the problem of predation by sharks.
How A Dolphin Uses Echolocation
When a dolphin is swimming, they use a low-frequency echolocation signal, which is made up of a pure tone. The tone is a click and acts like a ship’s echo sounder, helping the dolphin with information on the water depth, the profile of the seafloor, and the coastal areas.
The clicks they use scans the area, and the time interval between the sounds, along with the strength of the returning signals, give them this information. Dolphins use one click at a time, and this click must be sent out, and the echoes received back before the next click is sounded. If there is no echo, this gives the dolphin information as well.
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The length of time between clicks is the range at which the dolphin is trying to ‘see.’ The maximum range that the clicks can travel in the water is thought to be 800 meters. By waiting for the echoes to return, the dolphin can sense a few different things.
The dolphin can see the topographical information such as the depth of the ocean and the profile of the seafloor, and can also be used to locate any large animals in the water in the direction of the sounds it emits.
The echo that is returned first determines the distance and direction of the object that it has bounced off. Once the dolphin has determined this, they will then send out a further series of clicks.
This second set of clicks has a broad range of frequencies. Different frequencies will travel either shorter or further distances in the water, with high frequencies traveling the shortest distances as they are absorbed quicker by the water.
Once the dolphin knows the direction and the bearing of the target, they then send their clicks towards the object, whether it be a predator such as a shark or prey.
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To determine what the target is, the dolphins use the higher frequencies, which gives a better, more detailed image. Dolphins can also be seen to move their heads from side to side, which gives them further information on the size of the object they are concentrating on.
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Once the dolphin has swum closer to the target, the frequencies increase ever higher. This allows the dolphin to get a more detailed understanding of the object. At this point, the echolocation clicks sound more like a door creaking.
When the dolphin is very close, the echolocation can tell them very detailed information, such as the texture of the target.
Which Organs Do Dolphins Use For Echolocation?
Echolocation is a process of emitting sounds that sound like clicks, interpreting the returning echoes from the surrounding environment, thus giving the dolphin information on its surroundings.
Dolphins have a very sensitive hearing to locate where the sounds are coming from. They also use a range of low and high-frequency sounds to sense their surroundings.
Dolphins can locate objects outside of their visual range using echolocation. Dolphins hear the sounds of their clicks reflected back to them. Whereas humans rely on light that is reflected to us, sound waves carry more information to the dolphin.
Sound can give more of a three-dimensional picture than vision. The texture, structure, and material of an object combine to give a unique echo.
Dolphins have large fat deposits in their heads and lower jaws. Whereas most fat deposits are used for metabolic energy, the dolphin’s fat deposits in their head and lower jaw are not.
The skull of the dolphin has shaped throughout time to accommodate these fat deposits, and so scientists believe that these fat deposits are a big part of their echolocation.
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The fat deposits also have a different chemical composition from the other fat in the dolphin’s body.
Dolphins have a melon that is on top of their head in front of their brain. The melon houses the largest of these unique fat deposits.
The other, large deposit of this special fat, is located in the lower jaw where the jaw bone is thin. From the lower jaw, the fat deposit spreads up to the middle ear region.
It is believed that the melon and the lower jaw has a huge part to play in the echolocation used by a dolphin. In particular, it is the fat deposits in the lower jaw and in front of the brain that allows the dolphin to echolocate.
There are several steps to how a dolphin uses these to echolocate. First, the dolphin will make a sound that comes from a tissue complex in the nasal region. This is then transferred through the fat deposit in the melon, focussing the sound into a beam of sound.
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This beam of sound is directed into the water, and the echoes are received back. The echoes are received in the lower jaw, transferring through the fat deposit to the middle ear and up to the brain for the dolphin to interpret the results. The brain receives nerve impulses that relay the messages of sound.
The resulting echoes take a lot of interpretation, and for this reason, the brain of a dolphin is large for its body size. A large proportion of the dolphin’s brain capacity is used to interpret the results.
Frequencies of Dolphin Sounds
The frequencies of sounds that dolphins produce range from 0.2 to 150 kHz. The higher frequency clicks between 40 and 150 kHz are the sounds used in echolocation, although frequencies up to 130 kHz are most frequently used. The clicks last between 48 and 130 microseconds.
How Fast Do Dolphins Echolocate?
The speed of sound waves traveling through water is much quicker than through air. Through the air, the speed of sound is about 2.9 km/s, whereas, in water, the speed of sound travels about 1.5 km/s. Dolphins use this information to interpret the distance and size of the target.
Do Toothed Whales Use Echolocation?
Toothed whales do use the same methods for echolocation. Toothed whales are the only types of whales to hunt using echolocation. The use of sound waves to hunt their prey means that toothed whales do not have as many teeth as in the past, as they no longer rely on their teeth to capture food.
Do Baleen Whales Use Echolocation?
Baleen whales, such as blue whales and humpback whales have not adapted their sensory capabilities in the same way that dolphins and toothed whales have.
Although some species do emit a sound, the scientist believes that this is more for detecting water depth. This may make their long migrations easier if they can recognize features from previous migrations.
It is a possibility that the sounds and clicks that baleen whales use are a primitive form of echolocation as toothed whales had in the past. In the future, baleen whales may evolve their audio sense to use echolocation.
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