In this week’s episode, we will review breaking Dolphin News from around the world, focus our Science Spotlight on dolphin communication, and in our Kids’ Science Quickie, we’ll discuss cookie cutter sharks.
Men convicted of harassing a dolphin
The two British men accused of harassing Dave, a friendly dolphin often sighted off the coast of Kent, have been convicted by a British court. The two men reportedly swam with Dave early in the morning while returning home from an evening of drinking. They continued to swim with Dave even after authorities arrived and told tem to leave the water. Video of the incident shows Dave behaving aggressively toward the men, and showing signs of distress. Expert marine mammal witnesses testified that Dave was likely traumatized by the event. The two men were convicted of intentionally or recklessly disturbing a wild animal, and each were fined 350 pounds and sentenced to 120 hours of community service.
Listen to the science spotlight on dolphin communication:
Introduction to Communication
Before we discuss the many ways in which dolphins communicate, it is first important to get straight exactly what communication is. Quite simply, communication is the transmission of information . This is a broad definition that covers all of the many ways that the word ‘communication’ is used, not just in terms of living organisms. Modern technology is based on communication protocols that allow printers to communicate with computers, web browsers to communicate with web servers, GPS systems to communicate with satellites, etc. Each of these systems relies on a structured communication protocol that allows these computer devices to receive and understand instructions.
Animals too rely on structured communication systems to help transmit information. In fact, the ability to communicate information is ubiquitous in the animal kingdom : all life on this planet is able to communicate, both with other individuals of the same species, and with individuals of different species. The methods used for communication are varied and complicated, and are not limited to vocalizations. Ants for example share large amounts of information with other members of the colony through chemical trails and pheromones. Bees are known to communicate complicated information about the location of flower patches by engaging in an intricate ‘dance’ that lets other bees know the distance and direction of tasty nectar-rich flowers. (Bee Audio)
The bee waggle dance:
But communication need not necessarily always be thought of in these complex terms – sometimes messages are much simpler. A large bull moose, for example, grows enormous antlers that convey a relatively straight forward message: I’m big and strong – don’t mess with me! Communicating these kinds of simple messages is not restricted to the animal kingdom however. Flowers too communicate –many species of flowers demonstrate this ability when we take a special photograph using ultraviolet photography equipment. What may look like a beautiful solid-color yellow primrose or dandelion to the naked eye looks completely different when viewed in ultraviolet lighting conditions: intricate patterns and stripes lead into the center of the flower where the pollen is located. These patters evolved specifically to attract the attention of animals that see ultraviolet light – chiefly bees. (Bee Audio) In fact, much of a flower’s structure is designed to communicate information specifically with insects. (Bee Audio) OK, enough with the bees!
A flower photographed in ultraviolet light:
Complex multi-cellular organisms like bees (Bee Audio) hey!, flowers and humans rely on communication systems at the cellular level to function properly. Communication occurs between your brain and your muscles through tiny electrical currents flowing through your nerves. Cells in your body communicate information with other cells by releasing and receiving various proteins, and a breakdown in these communication channels leads to devastating problems like cancer and diabetes.
In fact, the ability to communicate is so commonplace for living beings that scientists are convinced that if alien life does exist, it too will have the ability to communicate. What’s more, scientists think that intelligent life, if there is any in the universe, will probably have developed mass communication abilities similar to that of humans, likely involving radio waves. The governments of the world are so sure of this idea that they have funded the multimillion dollar SETI project (Search for Extra Terrestrial Intelligence), which has spent 24 hours a day for the past few decades listening to the background noise of space with giant radiotelescopes hoping to hear something that resembles a communication signal from alien life forms. (Sci-Fi noise) So far, this is all they’ve heard. (Static)
Carl Sagan explains SETI:
So what then is language? In a previous episode of The Dolphin Pod , we discussed what the difference is between language and communication, so I won’t go into detail here. In brief, human language is a system of combining small meaningful elements into larger elements, forming phonemes, words and sentences that allow humans to convey infinitely complex amounts of information. After many years of study, scientists now think that some animals may possess small parts of this system within their own communication systems that allow them to generate some basic forms of human language-like communication, but nearly everyone agrees that only humans are able to learn and use language to the complicated extent that we know as ‘language’. The idea that we can plop a translation device onto a dolphin and turn their whistles into something akin to human language – like Darwin the Dolphin from Sea Quest – is science fiction (Darwin Audio)
Instead of human language, animals possess their own communication systems that allow them to transmit information. Scientists often define animal communication as follows: Bradbury & Vehrencamp (1998) provided this definition: “communication involves the provision of information (via a signal) by a sender to a receiver, and subsequent use of this information by the receiver in deciding how or whether to respond. As we have already discussed, these signals occur in many forms: a moose’s antlers signal that it is big and dangerous, changing the behavior of smaller moose – possibly discouraging them from entering into a fight. Bees transmit signals that tell other bees where flower patches are, influencing their behavior by encouraging them to fly out and have a look. These signals occur in different channels: for example, visual signals, auditory signals, chemical signals, etc. Scientists sometimes call these ‘modes’ of communication.
Dolphins produce a vast number of signals in a variety of modes which we will discuss here. The different channels or modes include: vocal signals, non-vocal auditory signals, visual signals and tactile signals. It is unlikely that dolphins transmit olfactory signals – those are signals that involve the sense of smell. Dolphins’ sense of smell is likely extremely restricted or entirely vanished, and their ability to smell underwater is probably non-existent. (Listen, Do you Smell Something ) There is a possibility that they may use taste to some extent – for example, dolphins may release chemicals into the water (e.g., from feces) that transmit information about arousal levels or reproductive status. But scientists aren’t too sure if this is the case.
Dolphin Communication – Vocal Cues
So let’s start by covering the most obvious form of communication that dolphins use: vocal signals. Dolphins produce two kinds of vocal signals: pure tones and pulsed sounds. Pure tones can take the form of whistles (Whistle), chirps (Chirp), screams (Wilhelm Scream) sorry – screams (Scream) and other continuous sounds that you are likely familiar with.
Scientists refer to these as ‘frequently modulated sounds’, which means that the pitch of the sound changes with time – rising and falling.
Scientist have leaned that dolphins are amazing vocal mimics – able to reproduce manmade whistle structures with precise accuracy. Dolphins produce whistles during social situations, when separated from friends, when excited, when happy and when panicked. Different whistles are produced in different situations, and scientists have been attempting to catalog and categorize whistles from study populations for some time. This is an extremely complicated process, and much has been written about how various species develop and use whistle communication. The whistles and other vocal calls of orca have received considerable attention, and scientists have discovered that family groups appear to reliably produce distinct categories of whistles and other calls that are stable across time, and that appear to be taught to new members of the group. These calls are so distinct that researchers are able to distinguish different family groups just by listening to their calls.
Here is an example of Orca Call Type N47 used almost exclusively by the A30 Matriline. (Orca Calls Here)
Scientists studying bottlenose dolphins have proposed the idea that each individual dolphin produces its own ‘signature whistle’ – a stable unique whistle structure that a dolphin develops during the first year of its life. Dolphins appear to be able to produce their own signature whistle quite reliably, but also the signature whistle of their friends. Isolated or lost dolphins appear to frantically produce signature whistles, apparently calling out to their friends. The jury is still out on the exact nature of the signature whistle however – some scientists believe that the whistles may not be all that stable – changing over time throughout a dolphin’s life. And it may be, like the orca, that these signature whistles are simply variations of shared whistles within a group. Regardless of the details, it is clear that whistles form an important basis from which much acoustic communication takes place between individuals. It should be noted however that there are a number of dolphin species which do not in fact produce any whistles whatsoever. These species are thought to communicate vocally using only pulsed sounds
Unlike whistles, pulsed sounds are brief sounds (called clicks) that occur in rapid succession at regular intervals. A series of clicks together is called a ‘click train’. Usually scientists classify these as either echolocation clicks, or ‘bursts pulses’. Echolocation clicks are used for sonar purposes (check out our episode on echolocation for more information ), and generally a dolphin will make a click and then wait for the echoes from that click to return before producing the next click. Echolocation is not a form of communication, but rather a method of ‘seeing’ the world through sound. By listening to the information coming back in the click echoes, dolphins can get a mental image of objects in their environment.
Burst pulses occur when dolphins release clicks so rapidly that it is not believe that they are able to gain any sonar information from the returning click echoes. Clicks can be released as high as 200 a second and still likely yield information for echolocation – but clicks released over that rate, and extending as rapidly as 2000 clicks per second – are thought to be communication signals, not echolocation signals. Dolphins of many species release bursts pulses when they are excited or angry, and burst pulses are thought to convey information about a dolphin’s emotional state. Some scientist have found a very specific burst signal produced by bottlenose dolphins that appears to be a ‘play’ signal – indicating to other dolphins that ‘it’s time to for games, so I’m not really being aggressive’. Burst pulses can be extremely loud, and dolphins may use them during aggressive encounters – possibly to hurt the ‘ears’ of other dolphins. Burst pulse sounds are often seen in social situation where males are herding female dolphins, where burst pulses are directed at the genital region of the fleeing females. They have also been observed when a mother emits a loud burst pulses directed at a misbehaving calf. Different kinds of burst pulse sounds used during aggressive encounters have been given names like ‘squawks’ and ‘barks’ – these click trains are often produced so rapidly that to the human ear, they sound like a continuous sounds, but in reality that are a series of tightly packed clicks. It’s not always easy to tell the difference between a burst pulse and an echolocation click train, and scientists are just now learning about how dolphins use burst pulses in social situations.
One interesting sound that we’ve discussed on previous episodes of the dolphin pod is the pop-creak sound that has been recorded from the Indo-Pacific dolphins around Mikura Island Japan. It sounds like a pop followed by what can be described as a bouncing ping-pong ball, and is often heard during aggressive chase encounters. Some scientists have described a similar pop sounds for other species as well – here is an example.
Non Vocal Acoustic Cues
Dolphins also produce a number of non-vocal sounds that they use for communication. Non-vocal in this sense means any sound that is not produced using the organs within a dolphin’s vocal area (e.g., air sacs, the larynx, etc) that nonetheless produce sound. For a human, screaming is a vocal sound, whereas clapping your hands together is a non-vocal sound. Here’s a list of non-vocal sounds that many species of dolphins use on a regular basis:
Tail slaps (or lob tailing): dolphins often hit the surface of the water with their tail (flukes), producing a very loud booming sound that can transmit great distances in the water. Often a tailslap is a sign of aggression, but this need not always be the case. Tail slaps may mean many things in many situations – for example, a signal that it is time to leave the area. It may simply be a means of getting the attention of friends who are some distance away. Some dolphins and whales also slap their tails as a means of hunting fish – stunning the fish with a powerful blow. This of course is not communication.
Flipper slaps: just like they would do with their tails, dolphins slap their flippers (that is, their pectoral fins) to sound. They may slap their flippers on the surface of the water, or onto their own body (e.g., their belly). This likely produces a similar effect to the tail slap.
Jaw claps and jaw pops: dolphins can produce extremely loud sounds by rapidly clamping their jaws together. This behavior bangs their teeth together, producing an acoustic signal that transmits large distances. Jaw claps are generally understood to be an aggressive signal, used as a threat. But jaw clapping also occurs during play – the difference between real aggression and play aggression is often very subtle, just like in the case of humans.
Chuffs: dolphins exhale rapidly, and you can often hear the sound of an exhaling dolphin if you happen to by nearby when they break the surface. Dolphins may also exhale rapidly through their blowhole as a communicative signal, producing a loud sound called a ‘chuff’ – a chuff is another signal thought to denote aggression.
Breaches: Many cetacean species engage in breaching behavior which includes part of the body or the entire body leaving the water before crashing back into the surface. Some Breaches produce loud sounds (sometimes called percussive sounds) with many low frequencies that travel long distances. Breaching may occur for a variety of reasons – possibly it is a method of removing remoras or other parasites, but more than likely it is a communicative signal. Breaching may produce sounds that convey information about emotional or motivations states, or the sound produced may tell distant friends about a dolphin’s position and the direction it is moving. Breaches may help herd prey during hunting situations. Spinner dolphins produce dramatic spinning leaps which also produce loud sounds upon re-entry – given that many of these leaps are performed at night, these may be leaps whose primary purpose is the generation of noise. Scientist have just begun to classify the subtle differences between types of breaching behavior, and are beginning to understand how small changes in the structure of the breach may in fact communicate vastly different information in various situations.
Humpack Whale Breaching:
Bubbles: dolphins often blow bubble streams and bubble clouds in a variety of social situations, and while these are primarily visual signals, the production of a large bubble cloud also produces a distinctive noise that can likely be heard over short distances.
Although humans generally tend to think of communication occurring with sound (thanks in part to our reliance on language), much communication happens within the visual modality – both for humans and for dolphins. Visual cues include everything from gestures to movements to coloration. Let’s explore some of the common visual signals used by dolphin species:
Body coloration, spots and stripes: many species of dolphins have evolved complicated body markings that communicate information. For example, Atlantic spotted dolphins slowly develop spots as they age, with adult dolphins being covered in mottled spot patterns – this quickly conveys information about a dolphin’s age. Many color patterns – like counter-shading and the distinctive black and white markings of orcas – are likely used for camouflage or to help when hunting prey species. However, some of the markings also help species to quickly tell the difference between animals belonging to the same or different species. Some species of dolphin like Risso’s dolphin, accumulate scars and bite marks after a lifetime of fighting with other animals, and the amount of scarring seen may indicate to others that the animal is either a veteran fighter, or low on the totem pole.
Sexual dimorphism: for many dolphin species, there is an obvious difference between the males and females of the same species. In general for most species, males are larger and bulkier, although specific body parts for species often differ between males and females, for example longer rostrums, darker colors, etc. Sometimes these signals evolve as a means of competition between males – larger males are larger because they need to fend off competition from other males. Male Amazon river dolphins accumulate scars all over their body which turns their skin bright pink, making it easier to pick out males from females. Male narwhals usually have a single long tusk – unlike females who rarely develop a tusk. This may be a signal to other males about the size and power of the individual sporting the biggest, manliest tusk. For the harbor porpoise, the female is actually larger than the male – but for the sperm whale, males are as much as three times larger than the females. These differences between the sexes signal vital information that individual use to determine how to approach social situations.
Postures: aside from static visual signals like coloration and body size, dolphins produce a number of visual signals. They can signal other dolphins with body postures – for example, by forming their body into an S-shape posture they convey anger or aggression. Some scientists speculate that this S posture is in fact an imitation of the S shaped posture assumed by sharks – something that also conveys aggressions for sharks. So in essence, dolphins may be pretending to be an angry shark. During aggressive encounters, dolphins will also flare out their pec fins in an attempt to make themselves look larger, and open up their jaws – a threat signal. We have witnessed an interesting behavior in Japan where a dolphin adopts a vertical position in the water, and slowly sinks to the sea floor without moving its body at all – the precise meaning of this position and behavior unknown.
Two dolphin groups fighting – pec flares, etc:
Bubbles: dolphin often release bubbles from their blowhole when making whistle sounds, although the release of bubbles does not always coincide with the production of whistles. Bubbles appear to be an extra communicative signal, and can take a variety of forms: bubble streams, bubble clouds, and bubble rings. A large bubble cloud is a conspicuous signal, and often is produced as a threat.
Dolphin blows a bubble cloud:
Gestures: dolphins of course do not have arms or hands, and yet they produce a number of subtle movements that could be understood to be meaningful gestures. For example, a dolphin shaking its head back and forth rapidly, an open jaw, or dipping its head during a frontal approach is often a sign of aggressions. Looking or swimming away, as well as flinching may be a sign of submission.
Dolphin jaw threat:
Synchronous behavior: dolphins have an unusual ability to imitate the behavior of other dolphins, as well as human researchers. In the wild it is thought that mirroring the behavior of your dolphin friends is a signal to other dolphins that the you are in a close relationship with your partners. Male alliances in Shark Bay Australia can synchronize their movements perfectly, breaking the surface and taking a breath at exactly the same time, and executing turns and twists underwater with perfect precision. This synchronous swimming displays constitute a strong visual signals to anyone who is watching. When groups of dolphins are stressed or threatened, they often group together and synchronize their behavior – perhaps to display solidarity and group cohesion.
Aerial Displays: We’ve already discussed how jumping out of the water created a percussive sound when the dolphin land on the water’s surface, but it also produced an impressive aerial display when the dolphins are airborne. These displays can be viewed both from above and below the water, and may be used to convey information about the direction of travel, location of food or general excitement levels. They may also serve to reinforce social bonds, and may also be effective in herding fish. Some have speculated that impressive aerial displays may also occur during contents – where individuals try to out-do each other.
Spinner dolphins jumping:
Object Carrying: Some dolphins in Australia have been observed using sponges as foraging tools – not a communicative signal at all, but in the Amazon River, the Boto (or animal river dolphin) has been seen carrying sticks and rocks in its mouth apparently as a visual display meant to wow potential mates. Males will collect objects and often swim out of the water holding the rocks or sticks in the air before slowly sinking back into the water. These object carrying displays may signal to the females that she has a hunky, strong male on her hands that is worth mating with.
A Boto carrying seaweed:
Poop: There is even one suggestion that dolphins might use poop as a visual signal! A few colleagues of ours from Japan have tested the idea that dolphins may poop directly in the path of human swimmers and other dolphins as a kind of warning signal. This ideas is still in the early stages of development, but it’s certainly worth noting!
Perhaps one of the most important modes of signaling in a dolphin’s world is the use of touch. Dolphins have skin that is quite sensitive to even the lightest touch – much like the skins of human beings. Dolphins are know to rub their bodies up against each other, but also to engage in intricate rubbing behaviors using the pectoral fins. Dolphins will rub their fins into the fins of other dolphins, engaging in a behavior that looks a lot like holding hands. They will also rub the bodies of their friends, moving their fins rapidly over the face, flank or genital region, producing what is likely to be a pleasurable sensation. Sometimes dolphins will seek out rubs by positioning their bodies under the fin of their friend. Researchers have observed a behavior where dolphins will rest their fin on the back of their friend, holding it in place for hours at a time – likely a signal to other dolphins of their friendship. Most all of the tactile behavior I mention here is thought to be a sign of friendly, affiliative contact.
But not all contact behavior is friendly. During aggressive encounters, dolphins can body slam each other, butt heads and ram each other with their rostrums. They also smack each other with their powerful flukes, and have even been observed leaping out of the water each other and slamming into each other while airborne. With sensitive skin, these kinds of aggressive contacts surely must hurt, and these are clearly aggressive signals.
Some people suggest that dolphins are able to share complex 3D images with each other using their echolocation, and often label this something like ‘holographic communication’. At present, there is no evidence that a dolphin’s echolocation ability is able to transmit anything like an image to other dolphins, so this suggestions is purely fanciful at this point. However, it has been shown that a dolphin who is positioned close to their friend can overhear the click echoes that are produced by their friend who may be echolocating on an object. By listening to these echoes, a listening dolphin might get a mental image of the object even though he/she is not engaging their own echolocation. This is not necessarily a form of communication – unless of course dolphins purposely echolocate on objects because they know that their friend will be receiving the click echoes. In this case, it may be something like communication – there is not yet any evidence that this is the case, although scientists are actively researching this area to learn just how dolphins use their echolocation in the wild.
There is of course much more that could be said about the ways in which dolphins communication, and I could talk for hours about this subject. But the information presented here should serve as a brief overview – enough to whet your appetite. For more information, have a look around the Dolphin Communication Project website, and listen to previous episodes of the Dolphin Pod where we cover some of these topics in more detail.
Kids’ Science Quickie: Cookie cutter sharks
Dolphins and sharks are by no means friends. In fact, after humans, sharks are probably the #1 killer of dolphins in the wild. But not all sharks are deadly – and some species of shark , like the cookie cutter shark, would prefer that their dolphin victims stay alive after an attack. The cookie cutter shark is a relatively small shark, and it makes its living by biting off small chunks of its victim’s flesh – usually in a circular pattern. By taking out a painful but not necessarily fatal plug of flesh from a dolphin, the shark will get its meal, and the dolphin will live to see another day, and possibly provide a second meal to the shark the next time it gets hungry. To see images of a cookie cutter shark and a dolphin with a cookie cutter shark bite, visit thedolphinpod.com
Cookie cutter sharks:
Cookie Cutter Shark Bite on a Dolphin:
Name a species of dolphin that does not produce any whistle sounds
The winner of last week’s quiz was voyager, who correctly stated that hind limbs can be seen in a developing dolphin embryo – these limbs will disappear by the time the dolphin is born. Now, for this week’s quiz: name a species of dolphin that does not produce any whistle sounds. Think you know the answer? Winners will randomly be chosen from the correct answers, and will be announced on next week’s show.
That’s it for this week’s edition of The Dolphin Pod – thanks for tuning in. If you would like more information about the stories from this week’s episode, check out thedolphinpod.com. If you’ve got questions or comments about this week’s podcast episode, please contact us through the website. Why not consider signing up for the Dolphin Communication Project’s online community? You’ get access to a forum where you can discuss the The Dolphin Pod with other listeners. The DCP website offers a chance to adopt one of our dolphins from the Bahamas, as well as learn more about volunteer, internship and ecotour opportunities.
Don’t forget to join us next week for more dolphin science news and info. And remember, the dolphin pod is only a click away.