In the Bahamas, spotted dolphins have to be on the look out for three species of sharks. The hammerhead shark, the tiger shark and the bull shark. Their best defense against these sharks is avoidance. Contrary to popular belief, dolphins do not seek out shark interactions. If they should be threatened by sharks, however, they can defend themselves with their strong rostrums and powerful flukes. Also, sharks in this area tend to travel alone, while dolphins travel in groups-anywhere from 3-30 dolphins. The more dolphins, the more eyes, ears and echolocation to keep an "eye" out for sharks! Aside from sharks, spotted dolphins in the Bahamas have to be concerned about fast boats. Boats that are driven erratically and fast than the dolphins can swim (up to 25 mph), put the dolphins at risk for painful and sometimes fatal propeller wounds. Improperly used and discarded fishing hooks and lines can also cause grave injuries to the dolphins. An important reason to remember to keep our oceans clean!

Dolphins are mammals. This means that they breathe air, give birth to live young and nurse those young. Fish however, lay eggs and breathe underwater through their gills. Sharks are a bit different. They are fish, but some give birth to live young. However, all sharks also breathe through their gills. Sharks' skeletons are made out of cartilage, not bones.

Although there have been reports of dolphins giving birth to twins, they most often give birth to one calf at a time.  When two dolphins are born together, one usually doesn't survive.  They can stay with mom until she gets pregnant again, between 3-5 years.  Gestation period is11-13 months.

A mom and newborn calf

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No, dolphins are very promiscuous. Males and females do not stay together; a calf will stay with its mother. Males are not involved in the care of calves.

Cetaceans is a collective term for whales, dolphins and porpoises. The name is derived from the scientific (Latin) name of these animals: Cetacea.

Dolphins are marine mammals, but there is also a fish species that's often called "dolphin" or "dolphin fish". Its scientific name is Coryphaena hippurus. To avoid confusion with the mammal species its Spanish name "dorado" or its Hawaiian name "mahi mahi" is often used. Because of the confusion between the mammal and the fish species dolphins have in the past erroneously been called porpoises, especially in some US regions, where the fish species is common. In older books you can encounter the name "bottlenose porpoise" for the bottlenose dolphin, for instance. Dolphins and porpoises are however members of different whale families. You can find more information about the dolphin fish, including its common name in other languages, in the FishBase database, online at http://www.fishbase.org/

There is not really one smallest species. The smallest species include: True dolphins (Delphinidae): * Tucuxi (Sotalia fluviatilis) - 1.3 to 1.8 m * Hector's dolphin (Cephalorhynchus hectori) - 1.2 to 1.5 m * Black dolphin (Cephalorhynchus eutropia) - 1.2 to 1.7 m * Commerson's dolphin (Cephalorhynchus commersonii) - 1.3 to 1.7 m River dolphins (Platanistidae): * Franciscana (Pontoporia blainvillei) - 1.3 to 1.7 m Porpoises (Phocoenidae): * Vaquita (Phocoena sinus) - 1.2 to 1.5 m * Finless porpoise (Neophocaena phocaenoides) - 1.2 to 1.9 m

The killer whale (Orcinus orca). Male killer whales can grow up to 9.6 m (31.5 ft). Spotted dolphins get to be about the size of a grown human-between 4-6 feet, up to 250 pounds. When they are born, they are much smaller-usually between 2-2.5 feet. Bottlenose dolphins grow to be between 6-8 feet.

The taxonomy of whales and dolphins is still subject to change. But in the most common view, the family of dolphins (Delphinidae) consists of 32 different species. Closely related families (the white whales (Monodontidae) and river dolphins (Platanistidae) have 2 resp. 5 species).

Most dolphins live in the ocean and the ocean water is too salty for them to drink. If they would drink sea water, they would actually use more water trying to get rid of the salt than they drank in the first place. Most of their water they get from their food (fish and squid). Also, when they metabolize (burn) their fat, water is released in the process. Their kidneys are also adapted to retaining as much water as possible. Although they live in water, they have live as desert animals, since they have no direct source of drinkable water. .

There are a number of dolphin species that live in fresh water. They all belong to the river dolphin families. These are: the Platanistidae (Ganges and Indus river dolphins), the Iniidae (the boto or Amazon river dolphin) and the Pontoporiidae (the baiji and the franciscana). There is one species that can be found both in fresh water (the Amazon river) and in coastal sea waters: the tucuxi (Sotalia fluviatilis). In general, salt water species don't do well in fresh water. They can survive for some time, but they will be come exhausted (since they have less buoyancy in fresh water) and after a while their skin will start to slough (like our own skin after spending a long time in the bathtub). source: P.G.H.Evans (1987) The Natural History of Whales and Dolphins. Christoper Helm Publishers, London.

The dolphin's fast cruising speed (a travelling speed they can maintain for quite a while) is about 3-3.5 m/s (6-7 knots, 11-12.5 km/hr). They can reach speeds of up to 4.6 m/s (9.3 knots, 16.5 km/hr) while travelling in this fashion. When they move faster, they will start jumping clear of the water (porpoising). They are actually saving energy by jumping. When chased by a speedboat, dolphins have been clocked at speeds of 7.3 m/s (14.6 knots, 26.3 km/hr), which they maintained for about 1500 meters, leaping constantly. Energetic studies have shown, that the most efficient travelling speed for dolphins is between 1.67 and 2.27 m/s (3.3-4.5 knots, 6.0-8.2 km/hr). There have been reports of dolphins travelling at much higher speeds, but these refer to dolphins being pushed along by the bow wave of a speeding boat. They were getting a free ride (their speed relative to the surrounding water was low). A recent study using based on the vertical speed during jumps showed maximum speeds for bottlenose dolphins of 8.2-11.2 m/s (16-22 knots, 29.5-40.3 km/hr) prior to a high jump. The maximum speed for wild bottlenose dolphins was 5.7 m/s (11 knots, 20.5 km/hr) and for common dolphins 6.7 m/s (13 knots, 24.1 km/hr). sources: D. Au & D. Weihs (1980) At high speeds dolphins save energy by leaping. Nature 284(5756): 548-550 J.J.Rohr, F.E.Fish and J.W. Gilpatrick, Jr. (2002) Maximum swim speeds of captive and free-rangings delphinids: critical analysis of extraordinary performance Marine Mammal Science 18(1):1-19 T.M.Williams, W.A.Friedl, J.A. Haun & N.K.Chun (1993) Balancing power and speed in bottlenose dolphins (Tursiops truncatus) in: I.L. Boyd (ed.) Marine Mammals - Advances in behavioural and population biology, pp. 383-394. Symposia of the Zoological Society of London No. 66. Clarendon Press, Oxford

The deepest dive ever recorded for a bottlenose dolphin was a 300 meters (990 feet). This was accomplished by Tuffy, a dolphin trained by the US Navy. Most likely dolphins do not dive very deep, though. Many bottlenose dolphins live in fairly shallow water. In the Sarasota Bay area, the dolphins spend a considarable time in waters that are less than 2 meters (7 feet) deep. Other whale and dolphin species are able to dive to much greater depths even. The pilot whale (Globicephala melaena) can dive to at least 600 meters (2000 feet) and a sperm whale (Physeter macrocephalus) has been found entangled in a cable at more that 900 meters (500 fathoms) depth. Recent studies on the behavior of belugas (Delphinapterus leucas) has revealed that they regulary dive to depths of 800 meters. The deepest dive recorded of a beluga was to 1250 meters. sources: F.G. Wood (1993) Marine mammals and man. R.B. Luce, Inc., Washington. E.J. Slijper (1979) Whales, 2nd edition. Cornell University Press, Ithaca, NY. (Revised re-issue of the 1958 publication: Walvissen, D.B. Centen, Amsterdam) R.S. Wells, A.B. Irvine & M.D. Scott (1980) The social ecology of inshore odontocetes. In: L.M. Herman (ed.) Cetacean Behavior. Mechanisms & functions, pp. 263-317. John Wiley & Sons, New York A.R. Martin (1996) Using satellite telemetry to aid the conservation and wise management of beluga (Delphinapterus leucas) populations subject to hunting. Paper presented at the 10th Annual Conference of the European Cetacean Society, March 11-13, 1996, Lisbon, Portugal.

If a single whale or dolphin strands, it usually is a very sick (and exhausted) animal. Such an animal often has some infections (pneumonia is almost always one of them) and a lot of parasites (worms in the nasal passages are very common). Sometimes these animals can be rehabilitated, but often they are so sick they won't make it. Some species of whales and dolphins occassionally strand in groups. A stranding of 2 or more animals is usually called a mass stranding. There are a number of theories that try to explain the occurrence of mass strandings. No theory can adequately explain all of them. In some cases it will be a combination of causes. The most common explanations are: * deep water animals (the species that most often are the victim of mass strandings) can not "see" a sloping sandy beach properly with its sonar. They detect the beach only when they are almost stranded already and they will panic and run aground. source: W.H. Dudok van Heel (1962) Sound and Cetacea. Neth. J. Sea Res. 1: 407-507 * whales and dolphins may be navigating by the earth's magnetic field. When the magnetic field is disturbed (this occurs at certain locations) the animals get lost and may run into a beach. source: M. Klinowska (1985) Cetacean live stranding sites relate to geomagnetic topography. Aquatic Mammals 11(1): 27-32 * in some highly social species, it may be that when the the group leader is sick and washes ashore, the other members try to stay close and eventually strand with the group leader. source: F.D. Robson (?) The way of the whale: why they strand. (unpublished manuscript) * when under severe stress or in panic, the animals may fall back to the behavior of their early ancestors and run to shore to find safety source: F.G. Wood (1979) The cetacean stranding phenomena: a hypothesis. In: J.B. Geraci & D.J. St. Aubin Biology of marine mammals: Insights through strandings. Marine Mammal Commission report no: MMC-77/13: pp. 129-188

The maximum age for bottlenose dolphins is between 40 and 50 years. The average age a dolphin can get (the life expectancy) can be calculated from the Annual Survival Rate (the percentage of animals alive at a certain point, that is still alive one year later). For the dolphin population in Sarasota Bay, the ASR has been measured to be about 0.961. This yields a life expectancy of about 25 years. For the population in the Indian/Banana River area, the ASR is between 0.908 and 0.931. This yields a life expectance between 10.3 and 14 years. So the actual life expectancy differs per region. Spotted dolphins don't do well in captivity and because a wild study hasn't been done long enough to tell exactly how long they live we have to guess based on what we do know so far. Generally speaking, the larger the dolphin species, the longer it lives. The orca whale is the largest dolphin yes it's a dolphin!) and can live for 80-90 years. Keep in mind that these are estimates and are based on ideal conditions. Sources: R.S. Wells & M.D. Scott (1990) Estimating bottlenose dolphin population parameters from individual identification and capture-release techniques. Report International Whaling Commission (Special Issue 12): 407-415 S.L.Hersch, D.K.Odell & E.D.Asper (1990) Bottlenose dolphin mortality patterns in the Indian/Banana River System of Florida in S. Leatherwood & R.R. Reeves: The Bottlenose Dolphin, pp. 155-164, Academic Press

Bottlenose dolphins eat several kinds of fish (including mullet, mackerel, herring, cod) and squid. The compostion of the diet depends very much on what is available in the area they live in and also on the season. The amount of fish they eat depends on the fish species they are feeding on: mackerel and herring have a very high fat content and consequently have a high caloric value, whereas squid has a very low caloric value, so to get the same energy intake (calories) they will need to eat much more if they feed on squid than if they feed on mackerel or herring. On average an adult dolphin will eat 4-9% of its body weight in fish, so a 250 kg (550 lb) dolphin will eat 10-22.5 kg (22-50 lb) fish per day.

To able to see colors, the retina must have at least 2 different kinds of cones, with different sensitivities. Most mammals have 2 types of cones: L-cones (sensitive to long-wavelength light, red to green) and S-cones (sentitive to short-wavelength light, blue to violet or near UV). Humans and some other primates have 3 types of cones, giving them a better color vision. Only a few landmammals have only one type of cone, which means they are colorblind. All these landmammals are essentially nocturnal animals. Whales and dolphins (as well as seals and sea lions) have only one type of cone: the L-cones. Although these cones are more sensitive for short-wavelength light than the L-cones of terrestrial mammals, they still have a very low sensitivity for blue light. And because there is only one type of cone, they are essentially colorblind (although in theory it is possible that there is a very limited form of colorvision in some light conditions, when both the rods and the cones are active). Reference: L. Peichl, G. Behrmann & R.H.H. Kröger (2001) For whales and seals the ocean is not blue: a visual pigment loss in marine mammals European Journal of Neuroscience, vol. 13: 1520-1528

To able to see colors, the retina must have at least 2 different kinds of cones, with different sensitivities. Most mammals have 2 types of cones: L-cones (sensitive to long-wavelength light, red to green) and S-cones (sentitive to short-wavelength light, blue to violet or near UV). Humans and some other primates have 3 types of cones, giving them a better color vision. Only a few landmammals have only one type of cone, which means they are colorblind. All these landmammals are essentially nocturnal animals. Whales and dolphins (as well as seals and sea lions) have only one type of cone: the L-cones. Although these cones are more sensitive for short-wavelength light than the L-cones of terrestrial mammals, they still have a very low sensitivity for blue light. And because there is only one type of cone, they are essentially colorblind (although in theory it is possible that there is a very limited form of colorvision in some light conditions, when both the rods and the cones are active). Reference: L. Peichl, G. Behrmann & R.H.H. Kröger (2001) For whales and seals the ocean is not blue: a visual pigment loss in marine mammals European Journal of Neuroscience, vol. 13: 1520-1528

Your breathing is controlled by parts of your brain called the medulla oblongata and the pons - they are located deep in your brain-stem down at the base of your brain. These little guys are in control of a lot of very important things that you do, including keeping your heart beating. And, you have them to thank every time you sneeze, swallow or blink - they control it all! Every second of every hour of every day the medulla oblongata and the pons are working hard to make sure that your body keeps trucking along. They never sleep - even when other parts of your brain do. We can, of course, take over conscious control of our own breathing - try it by holding your breath while you listen to this podcast. You have just relieved the medulla oblongata and the pons of their breathing duties. But, they are poised and ready to resume control of your breathing whenever you decide need them to. Isn't it nice to know that they will always be there for you? Here's an unsettling fact: for dolphins, the medulla oblongata and the pons do NOT control their breathing. Ever! In the dolphin brain, breathing is controlled consciously - that means that a dolphin has to think about every breath it wants to take before it takes it. This makes a lot of sense really - since dolphins spend their entire lives underwater, they need to think about and time exactly when they go up for air, so there is no real need for an involuntary breathing mechanism. But, that raises the following question: if a dolphin has to be awake and thinking about every breath it takes, how on earth do they sleep? A major flaw with this conscious breathing system is that if a dolphin ever really did fall asleep, it would simply stop breathing and die. The solution: never fall asleep! Or, at least in the case of dolphins, never sleep both halves of your brain at the same time. Dolphins, just like humans, have brains divided into two halves or 'hemispheres'. Over the years, they have evolved a neat little trick where they can put one half of their brain to sleep while the other half stays awake. The awake-half will then be able to control breathing and swimming, and other behaviors. For humans and dolphins, each eye is wired to the brain on the opposite side of the head. So the left eye is controlled by the right half of the brain and vice versa. When dolphins are resting, they sometimes close one eye - if you see a resting dolphin with her left eye closed, you can assume that the right side of her brain is asleep. But, the left half of her brain will be awake; controlling her breathing and making sure she doesn't suffocate or drown. And, quite literally, keeping one eye out for sharks. When dolphins rest, they usually swim quite slowly not too far from the surface, making it easier to swim up for a breath. Each brain half will get a chance to rest for a while before swapping with the other half. Generally, dolphins will rest like this for about 8 hours a day. Luckily for dolphins, the medulla oblongata and the pons are still in control of their heartbeat. Imagine how tiring it would be if you had to think about making your heart beat all day long. Some yoga masters claim to be able to control their heartbeat, but as for me - well, I am glad I am neither a dolphin nor a yoga master; I am happy to let the medulla oblongata and the pons run the whole show when I am asleep. Thanks guys! I'm also pretty happy I don't have to worry about sharks nibbling on me when I decided to take a nap.

If you are a regular listener to the Dolphin Pod, then you'll be aware of the power and versatility of a dolphin's echolocation system. If you are inclined to be jealous of the sensory systems of other animals, you could do worse than to envy dolphin biosonar. It is pretty cool stuff. At least, you can rest assured that humans outshine dolphins when it comes to vision, right? Not so fast my simian friend - while it is true that humans and other primates do have well-developed visual systems, our dolphin friends are not far behind. This episode will provide you with a detailed look at dolphins' sense of vision by focusing (get it, focusing?) on the structure of the eyeball. It is a head-to-head battle between the human and the dolphin eyeball to see who will earn the title of 'coolest eyeball ever'!

The Human Eye

In order to judge the merits of our two eyeball contestants, we first need to know a little more about eyeballs in general. It is important to note that not all eyeballs are created equal - each species on this planet that is able to receive sensory information through photosensitive cells organizes their hierarchy of tissue in slightly different ways. In fact, the eye, and other organs that function like eyes, has evolved at least 40 different times during the course of evolution. Dolphins and humans share a common mammalian ancestor more than 65 million years ago. Still, they are both built on more or less the same plan. The basic process for humans and dolphins works like this: light enters the eyeball by first passing through the cornea. The cornea is the outer layer of the eye, the shiny surface that you can touch with your finger, but that you shouldn't touch with your finger. The light then travels through the pupil, the pitch black opening in the center of your eye, and the lens - a kind of clear, rugby-ball-shaped tissue lurking just behind the pupil. The lens helps to focus light rays that pass through to the interior of the eye. The interior chamber of the eyeball is filled with a kind of liquid. Lining the back of the eyeball is a collection of cells that are capable of turning light into electrical impulses that travel to your brain. This layer of cells is called the retina. The process of allowing light in through the cornea and then the iris/pupil, and focusing it with the lens onto the retina, is basically how humans and dolphins are able to see. The real work of turning these electrical impulses into images that you actually use to see is done by your brain, and this is where things start to get complicated. Luckily for you, and for me, I will skip over this part for now, though wait for a future podcast that will focus on the brain and cognition.

Okay, now that you are an eyeball anatomy expert, it is time to learn how the dolphin eyeball differs from the human eyeball. First and foremost, there is a major difference in where the eyeball is located on a dolphin's head versus the human head. Humans have two eyes positioned in parallel at the front of our head; this is a typical position for the eyes of a hunting animal that requires depth perception. That is, 3D vision comprised of one visual field occupying about 180 degrees of visual space. Dolphins have their eyes placed laterally - on the sides of their heads. They can move each eye independently, which allows them to have two fields of vision. This is the kind of setup that most high-school teachers would love to have as it would allow them to keep one eye on the blackboard and the other focused on the classroom. This is just what dolphins can do; they can look in two different directions at the same time. Dolphins have 300-degree panoramic vision. This might sound strange, but it isn't that hard for the brain to process two separate visual fields coming from each of the two dolphin eyes at the same time. If one of your eyes should happen to fall out of your head, but you were still able to see with it, then you too would be able to see two visual fields at the same time. It probably would not be a very pleasant experience, but your brain would eventually get used to it. Brains are resilient. For example, in a few famous psychological experiments from the late 19th century, subjects were made to wear strange glasses that made them see the world flipped upside down. At first, this made them quite ill, but after a few hours, or in some cases a few days, the subjects started to see the world right side up again, even when wearing the glasses. Their brain(s) compensated for this weird information and made the world go back to normal. So, dolphins have the ability to see two visual fields at the same time, but they can also move their eyes so that these visual fields overlap, just like human vision. This likely gives them 3D (or bi-scopic) vision. The best position for dolphins to get bi-scopic vision is when they tilt their heads up and look underneath themselves, which is why you may often see dolphins tilting their heads upwards to get a good look at you with both eyes. Or, seeing them swimming upside down as they follow flying fish that are above the water's surface.

Dolphins are able to see under water quite well, thanks to a few handy adaptations for living in an underwater environment. In humans, the cornea helps to refract or bend light as it passes through the eye. It accomplishes this simply by the fact that light traveling in air bends as it enters the cornea, which, like the rest of the eye, is essentially filled with liquid. You will likely have seen what happens to light as it enters liquid if you have ever dangled your feet in the pool. You will notice how the strange bending of light makes your feet distorted, usually larger than they look in air. This is because the light is being bent (refracted) in funny ways as it hits the water, just like what happens when it hits the cornea. But for dolphins, the cornea doesn't bend the light at all because the light is already traveling in a liquid. It is the lens (just behind the pupil) that does all of the bending. A dolphin's lens is not shaped like a rugby-ball as is the human lens, it is much more spherical - like a little ball. This shape allows it to refract light much more dramatically, compensating for the lack of refraction that happens at the cornea. When humans swim under water, we have a difficult time seeing things clearly. This is because our cornea is used to bending light that hits our eyes directly from air, not from water. You might think that when a dolphin sticks its head out of water it might have the same problem in reverse, but this is in fact not the case. Even though their cornea is made for accepting light from water, the lens is able to compensate for this sudden shift from water to air - it moves back and forth in the eye, allowing a dolphin to focus in air almost as well as it can in water. This same kind of back and forth movement of the lens is what helps a dolphin focus under water, as well.

The pupil is that little black hole in your eye. If you have ever watched ER or any other medical emergency show, you will have seen doctors shine a light into a patient's eyes to see if the pupil changes size when exposed to the light (a sign that all is well with the hapless patient's brain). The human eye has an automatic mechanism that changes the size of the pupil, allowing in more light when it's dark and less light when it is bright outside. Dolphins have something much stranger going on with their pupil. Instead of a fancy mechanism that makes the hole larger or smaller, dolphins have a flap above the eye called an operculum. When light levels are high, the flap is pulled down over the eye, resulting in two dark spots on either side of the eye and not just one spot in the middle like in humans. And dolphins, like cats and dogs, have a layer of reflective cells behind their retina, called a tapetem lucidem, which reflects lost light back out past the retinal cells a second time. This makes it easier for dolphins to see in low light levels.

What about color vision? Well, there haven't been any experimental tests actually proving conclusively that they do or do not have color vision. But scientists have examined the kinds of cells found in a dolphin's retina and concluded that they are unlikely to have very good, if any, color vision. For animals that can see color, a special type of cell called a 'cone' cell can be found in the retina. Cone cells are sensitive to light occurring in different color spectrums. Humans have three different types of cone cells, which gives us pretty good color vision. Other animals that have color vision have as few as two types of cone cells. But poor old dolphins only have one type of cone cell, so if they have any color vision at all, it is likely limited to colors in the blue-green spectrum. Given that water absorbs colors like red and yellow easily, but lets blue and green though, it makes sense that dolphins only really need to see things in blue and green - the ocean is a blue/green world.

Well, this has been a close contest; the human and the dolphin eyeball have both proven worthy competitors. Humans certainly have the upper hand when it comes to cone cells, beating the dolphin eyeball hands down when it comes to color vision. But, the extra weird features of the dolphin eye give them a coolness factor that humans lack (like the ability to move each eye independently). In an eyeball competition, it is hard to say who would come out the winner. In fact, I think I am going to call this competition a tie. (boo) Hey! I call 'em as I see 'em.

Further reading:

Mass, A. M. and A. Y. Supin (2002). Vision. Encyclopedia of Marine Mammals. W. F. Perrin, B. Wursig and J. G. M. Thewissen. San Diego, Academic Press: 1280-1293.

Mass, A. M. and S. A.Ya (1995). "Ganglion cell topography of the retina in the bottlenosed dolphin, Tursiops truncatus." Brain Behav Evol. 45(5): 257-265.

van der Pol, Bert A.E., Jan G.F. Worst, and Pek van Andel. "Macro-anatomical Aspects of the Cetacean Eye and Its Imaging System." In Sensory Systems of Aquatic Mammals, edited by R.A. Kastelein, J.A. Thomas, and P.E. Nachtigall, pp. 409-414. Woerden, The Netherlands-. De Spil Publishers, 1995.

Mass, Alla M. and Alexander Ya. Supin. "Retinal Resolution in the Bottlenose Dolphin (Tursiops truncatus)." In Sensory Systems of Aquatic Mammals, edited by R.A. Kastelein, J.A. Thomas, and P.E. Nachtigall, pp. 419-425. Woerden, The Netherlands: De Spil
Publishers, 1995.

Ridgway, S. H. (1990). The Central Nervous System of the Bottlenose Dolphin. The Bottlenose Dolphin. S. Leatherwood and R. R. Reeves. San Diego, Academic Press, Inc: 69-97.

Have you ever wondered what the word for ‘dolphin’ was in other languages? Well, I’ve got a dictionary in front of me that provides simultaneous translations in 26 languages. Let’s have a quick look through, shall we? Let’s see… English: dolphin French: dauphin Italian: delfino Spanish: delfin German: delfin Dutch: dolfijn Swedish: delfin Lithuaina: delfina Hungarian: delfin Hey hold on a second, I think there might be a bit of a pattern here. The word ‘dolphin’ is pretty much the same in all of these languages. How can this be? Where did the word ‘dolphin’ come from that it became almost universal? In today’s episode, we will dig a bit deeper into this mystery to shed light on the ancient history of the word ‘dolphin’. The study of the science of language is called linguistics, but the study of the origin and history of words is called etymology. This is not to be confused with the word entomology, which is the study of insects. I suppose the study of the origin of the word insect would be entoetymology. Or that the study of the origin of the word for insects living on the planet Endor would be endorentoetymology … But, I digress... In our quest to solve the mystery of the origins of the word ‘dolphin’, our first step is to look up the word in a dictionary of Old English. Old English (otherwise called Anglo-Saxon) is the language spoken over 1,500 years ago in parts of what is present-day England. According to my dictionary, the Old English world for dolphin was … Delfin. Great. Well, this shows that “dolphin” has a root that is at least 1,500 years old in English, but that still doesn’t tell us where it came from originally. Incidentally, the world for dolphin in the many Celtic languages that were spoken at that same time in the British isles is not at all related to the word ‘dolphin’. In Early Irish, the word for dolphin is ‘muc mara’, and one of the words meaning ‘dolphin’ in Modern Welsh is ‘morwch’ (moruch). Both of these words translate into English as ‘sea pig’– a perfectly descriptive, though not very poetic, word for a dolphin. In fact, many of the world’s languages use a phrase that means ‘sea pig’ to describe dolphins - for example, ‘iruka’ in Japanese, and ‘hai tun’ in Chinese. The English word ‘porpoise’ also comes from Germanic roots meaning ‘sea pig’ or ‘pig fish’. So, where do those crazy Angles and those nutty Saxons get the word dolphin? And, what does it mean? Since our Old English dictionary was a bust, let’s have a look at an etymological dictionary – this should provide us with a detailed history of the word. The Online Etymological Dictionary gives the following definition: c.1350, from O.Fr. daulphin, from Middle Latin dolfinus, from Latin delphinus "dolphin," from Greek delphis (gen. delphinos) "dolphin," related to delphys "womb," Ahah! So, it looks like the Angles and the Saxons borrowed the word ‘dolphin’ from the Ancient French, who borrowed the word from the Medieval Latin speakers, who apparently borrowed the word dolphin from the Ancient Romans (those are the guys speaking classical Latin), who in turn borrowed the word from the Greeks. The word was then handed down across the ages as each of these languages evolved and blended in to each other. So, it was the Ancient Greeks that originally gave us the word dolphin! This means that the word ‘dolphin’ has been kicking around since about 1,200 BC (Homer used it in both the Iliad and the Odyssey). According to this explanation, the ancient Greek word for dolphin is related to the word delphys (delphus) meaning ‘womb’. In fact, in ancient Greek, the word ‘delphus’ means both dolphin AND womb. Womb? What on earth do dolphins have to do with wombs? A little snooping around, and I managed to find a variety of theories about the relationship between a womb and a dolphin. I say “theories” because once you starting looking at words that are over 3,000 years old, a lot of etymology turns into guesswork. There are simply no 3,000-year-old Greek people who we can ask, so the history of a word must be pieced together from the times we see it written down, or derived from what we do know about the elements that make up that word in modern usage. In this case, we know that the Greeks derived the word for those funny animals that they saw splashing around in the Mediterranean from the word meaning ‘womb’, although it is possible that people even more ancient than the Greeks first used a word like ‘womb’ to describe a dolphin. In any event, I’ve found a variety of possible explanations as to why this association exists: The first, that is the one that most dictionaries tend to favor is the relationship between the shape of a womb and the shape of a dolphin. That is, that a dolphin got its name by virtue of it resembling a womb. Maybe long long ago, an ancient Greek guy who was, for whatever reason, intimately familiar with the shape of internal organs, spied a dolphin frolicking in the waters and thought to himself “wow! That animal bears a striking resemblance to a uterus! I will tell all of my friends that and from now on this animal shall henceforth be known as ‘uterus’!” Well, it could have happened. The second explanation is the relationship between the word dolphin and the idea that the word “dolphin/womb” was used to describe fraternal associations in human relationships. The word Adelphi means ‘of the same womb’ – a reference to the idea that two brothers once shared their mother’s womb and hence a strong bond. This is the same word root that you will find in the word Philadelphia, the city of brotherly love. This explanation suggests that it was the fraternal and friendly behavior of the dolphins that caused the ancients to describe them as animals ‘of the womb’. On a similar note, another explanation would consider the dolphins to be ‘our brothers of the sea’, an idea that dolphins and humans share a special bond. There is no doubt that the ancient Greeks had special affinity for the friendly dolphin; they appear in Greek art and mythology. Also, note that the temple of Delphi – that most ancient of oracle – is renamed after the dolphin because of the temple’s association with Apollo, a powerful Greek god who often took the form of a dolphin and who took control of the temple that now bears his nickname. Lastly, there has been speculation that the Greeks called a dolphin a ‘womb fish’ for the simple reason that it was a kind of fish that had a womb, which is, of course, a uniquely mammalian organ. And also, that the reference to the womb is tied up with the idea that dolphins give birth to live young. But, these are just some of the many explanations for the link between womb and dolphin that are circulating out there. As any avid Google-searcher knows, the internet is awash with a plethora of wild ramblings, musings, speculation, and unsubstantial gobbledygook. Armchair bloggers are free to invent any old explanation that they want in order to explain the connection between womb and dolphin. One explanation I found claimed that the ancients called dolphins ‘wombs’ because of their connection with The Greys. The Greys are those iconic big-eyed aliens associated with Roswell and various autopsy videos who, in this theory, are born of the watery heavens, hence the reference to the womb. It so goes that The Greys are in fact descendants of ancient dolphin species – a ‘dolphin-based life form’. Since the dolphins are associated with the gods and the Grays are related to dolphins and dolphin means womb … oh never mind, I don’t know what the heck is going on with the explanation, but you get the idea. The point is that the word ‘dolphin’ is clearly related to the ancient Greek word ‘womb’ - for whatever reason. If you find that this association is too strange for you, feel free to switch over to the Celtic descriptions and call them ‘sea-pigs’.

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Check out our podcast episode on this topic.

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If you’ve been following the news lately, you might have seen a little story about elephants that can recognize themselves in mirrors. This is a rather major discovery for animal scientists – elephants now join dolphins as the only animals other than the great apes and humans that can recognize themselves in mirrors. Many scientists use the mirror self-recognition experiment as a test of an animal’s capacity for self-awareness – a trait often linked with cognitive complexity and intelligence. The mirror self-recognition test was pioneered by Gordon G. Gallup, Jr. – a psychologist from the University of Albany. In 1970, Gallup contributed a ground-breaking article to the journal Science showing that chimpanzees were able to recognize themselves in a mirror. His experiment, which has been used in modified forms ever since, works like this: you first allow the test subjects a few days to familiarize themselves with a mirror. It is during this time that, if the animal is up for the task, it will come to realize that the mirror is a reflection of its own image. Most animals will display ‘social’ behaviors at the mirror – as if they were encountering another animal, but if the animal manages to catch on to the concept of a mirror, these behavior will stop. After the animal is familiar with the mirror, researchers will give the animal some kind of visible mark on its body. If the animal appears to inspect the mark on its body by using the mirror, then voilà – you have mirror self-recognition. This has been tried successfully on elephants, all of the great apes species (like humans, chimpanzee, gorillas and orangutans), and, of primary interest to this podcast, dolphins! In 2001, Diana Reiss and Lori Marino performed the mirror self-recognition test on two dolphins at the New York aquarium. Similar to Gallup’s original experiment, the dolphins were marked with a temporary black ink after first having been exposed to mirrors. When marked, the dolphins twisted and turned and tried to look at the mark in the mirror – exhibiting behaviors similar to chimpanzees when inspecting their marks. In the 2006 study of elephants at the Bronx zoo, the elephants also spent a significant amount of time inspecting the marks in the mirror. The conclusion here: both dolphins and elephants can recognize themselves in mirrors. So, what’s all the fuss about? Well if you have ever seen a cat, dog, or bird attack its reflection in the mirror, you will realize that figuring out what mirrors are all about is usually considered beyond most animals. But the behaviors discovered in these experiments might be the result of something more important than just an ability to figure out what a mirror does. Many psychologists think that recognizing yourself in a mirror is the first step in a chain of abilities that leads to a Theory of Mind. Theory of Mind is a psychological ability that works like this: I know that I have my own mind with my own thoughts, beliefs and desires and consequently you must have your own mind with your own thoughts, beliefs and desires. Having a Theory of Mind is a powerful thing – it allows an animal to predict and manipulate the behavior of other animals, something at which humans are fantastically good. It also leads to advanced social emotions like empathy. So if an animal like a chimpanzee, elephant or dolphin can recognize itself in a mirror, this might mean that it is aware (or conscious) of itself. If it’s aware of itself, then it may be aware that it has its own thoughts, which means it might also be aware that other entities may also have their own thoughts: a Theory of Mind. Of course, it might not mean this it all – it could simply mean that the animal figured out some basic properties of mirrors without making any giant cognitive leaps. This is currently a topic of debate in the field of psychology. These experiments have provided important pieces of this puzzle. It is probably an important fact that all of the animals that have managed to perform this test so far; the great apes, dolphins, and now elephants – are all large-brained social animals; the most obvious candidates for benefiting from a Theory of Mind, and self-awareness. No matter how you interpret it, the results of these experiments are certainly remarkable.

As you may be aware, dolphins are able to use a special kind of sonar called echolocation or biosonar. In fact, all toothed cetaceans, that is - all of the whales, dolphins and porpoises that have teeth - are able to echolocate. Echolocation is the primary sense for most of these species; more important even than vision. And, if you think about it, that makes a lot of sense. You don't have to dive very deep in the ocean until light levels all but disappear. Many cetaceans live and hunt for food in a pitch-black environment. But, how does echolocation work? Well, would you be shocked to learn that dolphins echolocate by slapping their nostrils together? I thought so. However, I think this statement needs a bit of clarification. Here's a quick overview of the echolocation process for dolphins. A dolphin is able to produce click sounds, which are sent out into the water. Once these sounds hit an object, echoes are created; the dolphin then listens to these echoes and is able to form a kind of mental image of the object. But, how do nostrils fit into this process? Well to answer that question, I'll provide a not-so-quick overview of the echolocation process: A dolphin produces these click sounds using a structure in its head called the phonic or sonic lips. Humans, like nearly all mammals, produce sounds using their vocal cords. Dolphins do not have functional vocal cords; what's left of their vocal cords, called vocal folds, lost their ability to produce sound millions of years ago during their evolution from land animals. Instead, these phonic lips were evolved from what was once the dolphin's nose. Evolution has provided dolphins with a single opening at the top of its head through which it breathes - this opening is called a blowhole. The phonic lips (the former nostrils) are tucked just underneath the blowhole in the nasal cavity. By sending pressurized air past these lip-like structures, they are sent into vibration, and click sounds are produced. There are a series of nasal sacs in the dolphin's head that allows them to shuttle air back and forth across the phonic lips. Scientists studying dolphin echolocation were, for many decades, completely baffled as to how a dolphin managed to produce these clicks. No-one was sure exactly where in the dolphin's head these clicks were originating. The scientists thought possibly the clicks came from down in the larynx, in the nasal cavity, or maybe even from their blowhole. Thanks to a few relatively recent studies, scientists are now reasonably sure that the phonic lips are the source of clicks, although it is still a mystery as to exactly how pushing air across these lips results in the clicks themselves. Our best guess is that the lips (the former nostrils) slap against other fatty bodies in the dolphin's nasal cavity, which then transfer the sounds through the dolphin's head and out into the water. Since dolphins have two sets of phonic lips (having evolved from each of the two nostrils), they are able to produce two sets of click sounds simultaneously. This means that they can produce two sets of click sounds simultaneously, as well as whistle sounds which are produced in the larynx. Dolphins are great multi-taskers when it comes to sound production! Click sounds are very short in duration - between 40 and 70 microseconds, but they can be very very loud; around 220 decibels for bottlenose dolphins. Dolphins usually produce clicks in a rapid series called a 'click train'. These click trains can consist of hundreds, sometimes even thousands of clicks per second. Here is an example of a dolphin's echolocation click train. (Play Sound) These click sounds contain very high frequencies - some of them well above the range of human hearing, above 120 kHz. You can learn more about dolphin hearing range in a previous episode of The Dolphin Pod called So High it Hertz. Although high frequencies don't travel as far as low frequencies, these high frequencies with very short wavelengths allow a dolphin to echolocate on small objects and pick out fine detail - the higher the frequencies, the better the detail. This allows a dolphin to locate and track tiny prey species. The sperm whale, a toothed cetacean that is also able to echolocate, relies on its echolocation during deep dives into pitch black waters in order to locate and track much larger prey. The sperm whale can use its louder, lower frequency echolocation clicks to locate giant squid and other prey over long distances - possibly even several kilometers. But, back to dolphin echolocation: click sounds produced by a dolphin are directed out through the front of the dolphin's head. They first pass through special fatty tissue called the melon. This is that lump you see at the front of a dolphin's head that looks like a big rounded forehead. The melon is filled with a kind of lipid called acoustic fat, which has the same density as seawater. The dolphin can change the shape of her melon as the click sounds pass through it - in this manner, the melon acts as an acoustic lens: the click sounds are formed into a kind of cone-shaped beam that extends out in front of the dolphin. This is very loosely a bit like a flashlight beam. The dolphin can direct this beam of sound toward objects that it is investigating, like a human diver, for instance. As each of the clicks hits the diver and bounces off, a click echo is produced, which then heads back toward the dolphin. A dolphin actually receives sound through its lower jaw. A dolphin's jaw is filled with the same kind of acoustic fat that is found in the melon; this allows for sounds to be transmitted up the jaw and toward the dolphin's middle ear. The echolocation process - sending out clicks and listening to the click echoes - is what produces a kind of mental image of the object that a dolphin is investigating with clicks. We know that the changes in the structure of the click echoes are what a dolphin uses to form this mental image, although it is still an unsolved mystery exactly how they manage to accomplish it. This echolocation 'image' is unlikely to be something that a human being could imagine simply because people can't echolocate. But, this "mental image" is currently the best analogy we've got. Scientists have learned from experiments with dolphin echolocation that their acoustic image is quite detailed, and allows a dolphin to do some pretty amazing things. Some experiments into what is called cross-modal matching have revealed that dolphins are able to identify an object using vision that they had previously only been able to learn about using echolocation, and vice-versa. Cross-modal matching is something you can test for in humans, too - you can try it yourself, here's how. Blindfold your friend and give them an object to inspect with their hands, like an orange. Your friend will then be able to form a kind of mental image of the orange using the tactile sensory information sent to their brain from their hands. Now, take the orange away from them and remove the blindfold. Hold up both the orange, and another object - like a spoon, and ask your friend which object they were just holding. Your friend will likely be able to say that it was the orange. Even though they never saw the orange, they formed a kind of mental image of the orange using the information from another sense or modality (touch, in the case of the orange). Dolphins can do something just like this, but across the senses of vision and echolocation. What's unique and handy about echolocation is that a dolphin can use it to sense the density of objects, as well as discriminate between objects of differing compositions. Echolocation clicks can penetrate soft structures like the sand … and maybe even the diver's body! This is about as close to X-ray vision as any animal is going to get! If you have ever had the chance to swim with dolphins, you might have been able to feel a dolphin's echolocation on your skin. For species like bottlenose dolphins, you can usually hear their echolocation underwater - but not always. Sometimes the clicks they use are too high in frequency to hear. You can usually tell when a dolphin is echolocating, however. They often move their heads slowly back and forth as they scan with their echolocation. This is called 'head-scanning' - as they change their head position, the click echoes also change structure, which helps the dolphin to get an image of what it is looking at. Or, do I mean listening at? So, there you have it, A not so quick overview of dolphin echolocation. There is, however, much more to be said about this subject, and we will explore this amazing dolphin sense in more detail in upcoming episodes of The Dolphin Pod. In the meantime, you can impress your friends by telling them that dolphins produce echolocation clicks with their nostrils. Surely that is a useful bit of information for your next cocktail party.

Have you ever had that feeling where you are talking to someone at a party and you are sure that you have met them before but you just can’t seem to place them? Did you meet them at your cousin’s wedding last summer maybe? Did they go to elementary school with you perhaps? This can be frustrating. Now take that feeling and multiply it by about a million, and you will have a pretty good idea what it feels like as a scientist trying to identify individual dolphins. Dolphins, unlike humans, rarely wear nametags, they never style their hair into a unique coiffure that make them easy to pick out in a crowd, and you won’t ever be able to recognize a dolphin because of the shoes it is wearing. For scientists studying wild dolphin populations, being able to identify individual dolphins is a vital component of their research. Studies gathering information about individual dolphins are used for research on population size estimations, migration patterns, social structure, group movements, life histories, and behavior. For example; researchers may be interested in learning how often individuals within a group interact with other individuals – patterns of association. Scientists may want to learn what kinds of behaviors are being produced by the adults, the juveniles, the males, the females and so on – all of this requires the scientist to know and recognize which individual dolphins they are observing. To do this, researchers rely on a variety of identification or “ID” techniques. The most popular technique is photographing the dorsal fin of the dolphin as it breaks the surface to breathe – this is often called photo-ID. Dorsal fins can function a lot like human fingerprints – the notches and nicks along the edge of the fin allow researchers to recognize and categorize individuals. This technique is very handy for species that don’t really like the presence of boats – researchers can use telephoto lenses to capture a picture of a dorsal fin from a greater distance. There is even some pretty fancy computer software that will help researchers search through scanned dorsal fin images to try and match photographs to the fins of previously identified dolphins. Some dolphin species will have natural markings or coloring patters that are visible when they surface, and these can be used for ID as well. For those scientists able to actually enter the water to film or photograph wild dolphins under water, or for those using an underwater camera from their boat, it is possible to identify dolphins based on a variety of body features. Sometimes deformities like missing fins or a prominent under-bite can be used to ID individuals. Wild dolphins accumulate a huge variety of scars and marks throughout their lifetime: everything from shark bites to cuts and scratches from contact with rocks, and even injuries resulting from fights with other dolphins. If the dolphin is unlucky enough to have a nasty scar, or a chunk missing from its fluke, a scientist will have a relatively easy time re-identifying this individual based on underwater video or still photos. For the Indo-Pacific bottlenose dolphins that the Dolphin Communication Project studies around Mikura Island, scars from shark bites are all too common. One shark in particular, the cookie cutter shark, is known for taking a nasty circular bite out of the dolphin’s flesh – it leaves a prominent scar that makes it very easy to recognize specific individuals. For images of cookie cutter and other shark bite scars from the Mikura dolphins, check out The Dolphin Pod website for links. Shark bite images Cookie cutter shark bite images The trick is of course finding scars that are going to stick around for a few years – many species of dolphins are covered in ‘rake marks’ – these are shallow scars caused by the teeth of other dolphins, and they occur when dolphins are fighting or playing with each other. Since rake marks are often shallow, they will only be visible for a few weeks to a few months, and are not a reliable way to identify individuals over longer periods of time (i.e., between years). Some species of dolphins, like spotted dolphins, develop spots as they age. If researchers remain vigilant and keep clear records of the development of these spots over years, these distinctive spot patterns will allow them to reliably recognize individuals. The key to being able to identify individual dolphins is keeping good records – well organized photographic and video records are invaluable. Many scientists will keep a book with sketches of individual dolphins that can be easily updated as dolphins accumulate new scars. Individual dolphins are typically assigned names and/or numbers. To learn about some of the research groups working on identifying individual dolphins as part of their research, visit The Dolphin Pod website for links. There is even a link to an online test to see how skilled you are at identifying individual dolphin dorsal fins. http://www.cbmwc.org/research/photo_id_interact.asp Of course, these kinds of ID techniques could be used to avoid the predicament described at the start of this episode. Imagine how handy it would be if, when you came across that person at the party who you just couldn’t place, you pulled out your photo-ID book and flipped through until you found out who they were. “Ah yes, your name is Todd Johnson – I lasted sighted you on June 15 at the Henderson’s housewarming party. You were seen associating with an adult female and two juvenile males. How have you been, Todd?”

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Did you know that a killer whale, otherwise known as an orca, is actually a dolphin? Orcas are in fact the largest dolphin species in the world today. So, why are they called whales and not killer dolphins? Which, by the way, sounds downright terrifying? Well, that is a good question, and there is no easy answer. So instead of an easy answer, here is a complicated one: There are around 35 species of oceanic dolphin. All of these species can be correctly referred to as dolphins because they are in the scientific family known as delphinidae. Species in this family all have cone shaped teeth, a single blowhole on the top of the head, among other morphological traits that separate them from the other families. What makes this a little confusing is that the common name for many of these dolphin species as the word whale in the name. The killer whale is a fine example. But there are more, including the melon-headed whale, the pygmy killer whale, the false killer whale, the long-finned pilot whale, and the short-finned pilot whale. To complicate the issue even further, all of the species I just listed are sometimes called blackfish, although they are of course not actually fish, and not really whales, but simply dolphins. You think that us confusing? Try figuring out how the word porpoise fits in. In North America, many people refer to dolphins (the species in the family delphinidae) as porpoises. They may even call a bottlenose dolphin, the most famous dolphin of all, simply a porpoise. This term came about from fisherman who call most dolphin species a porpoise to differentiate between them and the dolphin fish, otherwise known as mahi-mahi. Now the problem is that science recognizes the porpoise as a different kind of animal altogether. There is a scientific family known as phocoenidae that contains 6 species of what are officially known in science as porpoises. So to be scientifically proper, a porpoise is an animal belonging to the phocoenidae family, and the term porpoise should only be used to describe one of those 6 species. Unless of course you are a fisherman and you want to call a melon-headed whale a porpoise, which you might do, even though it is actually a blackfish or officially a dolphin. But let us return to the first question: what us a whale? Well according to official scientific terminology, there is no such thing as a whale at all. Science does not formally use the standalone word whale to refer to any of the animals found in the scientific order cetacea; that is the order containing all animals commonly referred to as whales, dolphins and porpoises. The term whale is usually used in the common name of the largest of the animals in the order cetacea, including the blue whale, the sperm whale and the beluga whale. That is because the word whale in English was in use for many centuries before scientists came on the scene and tried classify all of the cetaceans, and it was probably applied rather indiscriminately to most large animals seen swimming in the oceans. Nowadays, a scientist might refer to animals like the blue whale (the species with baleen instead of teeth and grooves on their throats) as rorquals, or they might call the Sperm whale by the name Physeter. Because common names often vary from place to place and language to language, the only way to be sure of what animal you are talking about is to use its scientific name. In English, a Killer Whale therefore was probably originally referred to as a whale simply because it is large; it otherwise has very little in common with an animal like the Blue whale. As we now know, science recognizes the Killer Whale as a dolphin because it is in the delphinidae family. But here is one more snag: there are 5 species of freshwater river dolphins that are NOT in the dolphin family, but in separate families altogether. These river dolphins are nonetheless correctly referred to as dolphins. As you can see, it us not easy to tell a dolphin from a whale. When in doubt, you can always just shout 'hey, look - there's a cetacean! ' Maybe that us cheating, but at least you will be correct! Wouldn't it be easier if we all just spoke Latin?

You may be aware that dogs have a hearing range well above that of human beings - they are capable of hearing high frequencies that humans simply are not able to hear. But, did you know that dolphins have a hearing range that far exceeds that of humans and even dogs? In fact, dolphins are able to hear, and to produce, some of the highest frequency sounds of all mammals. Let's put this into perspective. Humans have a hearing range of around 20 Hz to 20kHz. (that is, 20,000Hz) The Hertz scale is a measure of how many times a second a sound wave is produced.. Here is an example of a 60 Hz sound [play sound] - that is, 60 sound wave cycles per second. The human voice produces a range of frequencies when we speak, but the main frequencies are between 500Hz and 2 kHz. Here is an example of a 1 kHz tone [play sound] - a tone that is pretty easy for humans to hear. The top range of human hearing is up around 18 or 20 kHz - depending on your age and gender. As humans get older, we begin to lose our ability to hear these higher frequencies. I will now play an example of a 15kHz tone [play sound]. Did you hear it? If not, it might be an indication that you are getting on in years. Of course, it is possible that your speakers or headphones are not able to produce a tone that high, so for now, let's blame it on the speakers. So what about dogs? Well, dogs are able to hear frequencies more than twice as high as humans - up around an impressive 45 kHz. But dolphins can do even better than that! For the species whose hearing has been researched the most, the bottlenose dolphin, we know that they can hear frequencies as high as 150kHz. Yes, that's right - 150kHz! If a jump from 1 kHz to 10 kHz sounds like this [play sounds], can you imagine how much higher 150kHz must be? Dolphins use high frequency click sounds as part of their echolocation, producing and listening to sounds in these high frequency ranges. These clicks can sometimes be heard by the human ear because they contain frequencies below 20kHz, but the loudest frequencies produced in a click are up around 120 kHz. These high frequencies help a dolphin to pick out fine detail when is uses its echolocation to investigate an object. There is one other mammal that can best the dolphin when it comes to producing and hearing high frequencies: the bat. Bats can produce and hear frequencies as high as 250kHz! Now that is a frequency response that not even the most expense 5.1 surround sound home cinema would be able to cope with.

Can dolphins kill or stun prey with loud sounds? It certainly seems that way if you believe following headlines: Dolphins' killer sonar confirmed from ABC Science Online February 2001. Killer clicks from New Scientist 1 January 2001. These are, of course, thrilling headlines and far more interesting than the contents of the research papers that they describe. Why quote the following tedious academic prose: "The propagation of click echoes vis-�-vis the contours and composition of the ensonified object must also be considered when conceptualizing efficacious listening positions" When you can say Mysterious monsters are killing fish with murderous death beams as appeared in The Santa Cruz County Sentinel. However, sometimes reality can indeed live up to the hype - 'stunning prey with a blast of sound' is something that happens every day in the ocean. The diminutive snapping shrimp is capable of producing a 200 dB blast using its specially designed claw, rendering unconscious any unsuspecting prey that happen to be passing by. But, can dolphins do something similar? The hypothesis that dolphins can use loud bangs or deafening click sounds to debilitate, stun or even kill their prey has been kicking around the scientific world since the 1980s. It is known as the 'acoustic prey debilitation' hypothesis, and was first introduced in a popular article by Ken Norris and Bertel Mohl that appeared in The American Naturalist in 1983. This hypothesis addressed the question of how sperm whales, with their flimsy looking jaws, were able to capture and eat the fearsome giant squid that kept turning up in their stomachs. These squid typically had no teeth marks on them at all, which begs the question; how did these whales manage to catch and then swallow an entire giant squid seemingly without a struggle? One possible explanation was that they used loud sounds to debilitate the squid so they could slurp them up without a fight. This hypothesis became very popular with the media (as we have seen), but actual real live scientific evidence to support it was strikingly absent for decades. Nobody had ever actually seen a sperm whale or dolphin do anything like this! 20 years later or so, a group of scientists led by Ken Marten published an article in the journal Aquatic Mammals detailing some initial evidence that dolphins might be making a variety of sounds to stun their prey before gobbling them up. But, conclusive proof was still lacking. However, new evidence from a paper just published in August 2006 in the Journal of the Acoustical Society of America provides some rather convincing evidence that seems to blow the acoustic prey debilitation hypothesis (also known as the prey stunning hypothesis) out of the water - so to speak. A research team led by Kelly Benoit-Bird performed a series of simple experiments: herring, cod and sea bass - some of the favorite food of dolphins - were placed in water tanks with video cameras recording their every movement. Click sounds recorded from real dolphins; both orcas and bottlenose dolphins, were played back to the fish at varying intensity levels and repetition rates. The result: no matter what the researchers threw at them, the fish didn't seem in the least bit bothered by all the fuss. Even with clicks being played back at the highest volume that dolphins are capable of producing, the fish didn't even flinch. It seems that dolphin sounds simply don't have the oomph to rightfully be called a 'killer licks. Is this the final chapter in the 'killer sonar' book? Probably not. Although this latest paper seems to prove that dolphins can not stun or kill their prey with sound, you never know when someone will dig up new evidence to prove that they can. That's the beauty of science! It isn't the nail in the coffin just yet, but it is certainly seems that Killer Clicks are not all that they're cracked up to be.