It is of interest to note that while some dolphins are reported to have learned English—up to fifty words used in correct context—no human being has been reported to have learned dolphinese.
ATTRIBUTED TO CARL SAGAN
Esteban had Alita in his sights. She was the newest female in the group and the only one who was very pregnant. Try as he might to wiggle his way past the other females of the group, they simply would not let him pass. Esteban’s frustration was mounting, as evidenced by his whistles, clicks, and jerky movements around Gracie, Rita, Mrs. Beasely, GeeGee, and Cedena—Alita’s elite guard against Esteban’s amorous intent. Suddenly, Esteban did a sharp U-turn, stopped vertical in the water column not more than 6 feet (2 m) from me, and began clapping his jaws together in my direction! It is not every day that a large male bottlenose dolphin jaw claps at you. Jaw claps from adult males are often considered a sign of aggression, a distinct signal to “back off” or “get out of the way.” My reaction could not have been more opposite: I kept filming and did not budge. Esteban jaw clapped for about thirty seconds and then zoomed out of sight. Hindsight had me rethinking my response, and I have revisited the action in my mind. Esteban was so frustrated, I think, that he needed to express his irritation at the nearest being, me. That is, he seemed to be “venting” about his situation before leaving to pursue some other behavior.1 In Esteban’s situation, his jerky movements and vocal signals were likely intended to send a message to the adult females barricading him from Alita. He wanted access to Alita. But could the same be said for his jaw claps at me? Was Esteban trying to send a message to the first being he encountered after being rebuffed? Or was he just “letting off steam”?— Kathleen
Communication is the cement that binds all animal societies. Every day we share information with family members, friends, and business associates, not to mention numerous strangers in stores, gas stations, and other places. I (Kathleen) believe that Esteban was trying to communicate with Alita and the other female dolphins, though I cannot say the same for his actions toward me. That is, Esteban’s jaw claps seemed more like the phrases my husband utters in my direction when his attempts to fix a “sensor error” on our car go awry. This is more “self-communication” or expression than an attempt to share information with another being.
Conversely, I (Toni) have interpreted this same dolphin jaw clap behavior somewhat differently, as a threat or warning, albeit in different situations than that which Kathleen describes. I have observed instances of dolphins jaw clapping at another dolphin or person, though I have not yet been the recipient of this behavior. In a few of my observations, the jaw-clapping dolphins also directed forceful, intentional physical impact (such as biting or ramming) toward a recipient, that is, the other dolphin or person. When these aggressive behaviors followed jaw claps, the recipient did not retreat or back down (which I think makes Kathleen a lucky person). I have also seen a young wild beluga clap her jaws toward a human swimmer who didn’t know better, thought the behavior was “cute,” and did not retreat. If the behavior was a threat, the beluga did not follow through, but she did leave the area shortly thereafter. So perhaps when signals are meant as threats, the threats are not always followed through . . . or, maybe they are bluff and bluster. And as Kathleen suggests, sometimes dolphins that exhibit this behavior are really exhibiting frustration or stress rather than conveying an intentional signal. The question remains, how do we as observers, and other dolphins, know the difference?
What would life be like if we could not communicate our wants and feelings to others? It would certainly be immeasurably more complicated and difficult, if not impossible. Social behavior is organized into patterns of coordinated behaviors and activities. To understand communication in a particular animal or species, we need to learn what, how, when, and why certain signals are used. In other words, we must discover and analyze as many basics of animal communication as we can get our hands, eyes, and ears on.
Some basic building blocks will help clarify the nuances of communication and the study of how other social animals use information to survive the murky waters of society.2 Three pieces of information are critical in the study and comprehension of communication: the signal, the signal sender, and the signal receiver. The signal is the vehicle (the “what” and “how”) by which the sender and the receiver exchange information. The sender and receiver must exchange signals accurately to avoid missing the message, which would cause miscommunication. Signals can be subtle, such as an animal’s display of a unique color pattern or a slight change in body position. Or signals can be more dramatic. Think of a lion’s loud roar or a dolphin slapping its tail to warn an intruder. Signals are often accentuated by other behaviors, and sometimes the sum may be more than the total of its parts. Play behavior in dogs and other animals includes bites and growls combined with play bows—without the play bow, the associated actions could perhaps indicate the opposite of play. When we see a growling dog with bared teeth, it might also have its tail straight and not wagging, and the hair along its back might be standing on end. Taken together, the meaning of these signals would be hard to misinterpret, even across species.
A signal can be modified based on location, distance between participants, past experience, age, sex, reproductive status, environmental factors, presence of peers, quality and history of relationship with others, and other factors, including the “mood” of the senders and receivers. Therefore, the meaning that a signal conveys relies on contextual cues that are crucial to imparting the correct message. A signal given in one context could result in a different meaning in another: a “jaw pop” from a dolphin might be used to threaten an intruder in one situation or reprimand a youngster in another circumstance.3 A dolphin’s leap out of the water may signal to other dolphins that fish are nearby whereas a slightly different breach may signify play. A signal conveys both a message and a meaning—the nuts and bolts of a communication exchange, so to speak. The message is the information provided by the sender, whereas the meaning is the significance attached to that signal by the receiver and varies by context.
Many species throughout the animal kingdom are capable of sophisticated communication. Through what is referred to as a “waggle dance,” bees signal the presence, abundance, and location of food to other members of the hive.4 Researchers Joyce Poole and Cynthia Moss have noted combinations of elephant matriarch vocal rumbles associated with actions that appear to communicate the direction of travel for the group. Poole suggests that these vocalizations may constitute a word as defined by primatologist Sue Savage-Rumbaugh.5
When we study communication, the signal is the most discernible part of the exchange, but how the receiver perceives and responds to a signal is just as important. The message and meaning of a signal are not always the same; different receivers may acknowledge very different information from the same signals, and contextual cues play an important role. To give an example in human communication, consider walking through an airport terminal. You see people waving to or hugging other people. Are they saying “good-bye” or “hello, welcome home”? The mechanism for miscommunication is similar (same bolts) yet different (nuts). For example, a man who is wearing a new suit hears a good friend tell him that he looks “unusually handsome” and takes it as a compliment; in contrast, if a competitor at work says the same thing to him, he may interpret the remark as an insult—even if it was intended as a compliment. The social context of the latter session could lead to misinterpretation. In evolutionary terms, these are everyday signals that humans use to strengthen bonds between friends and family members. Most signals have evolved to address specific problems or meet certain needs in social behavior, such as finding a mate and coordinating efforts in searching and capturing prey. Senders choose from multiple sensory abilities to encode a specific signal, while receivers use their own diverse sensory set to decipher the meaning of each signal.
Communication can occur via a single sensory mode or by a combination of multiple sensory modes. These can include visual, acoustic, gustatory, tactile, and olfactory signals. For humans, gestures or postures, such as standing with one’s hands on hips or shaking a pointed finger at someone, can modify a verbal message or even convey one on their own. A handshake, hug, or pat on the back following a conversation often conveys more about the relationship between the individuals and their intentions than the conversation itself. Touch occurs with any body part, but some areas have special significance.
How might dolphins use their pectoral fins to share information? When one dolphin places its flipper on another’s side between the dorsal fin and the tail, it may be requesting something. The actual “favor” being asked depends on the context, but the touching dolphin initiates the request with its flipper. To appease an excited youngster, adult dolphins will often rub the young animal’s melon (forehead) with a flipper. Young spotted and bottlenose dolphins often swim excitedly around peers and humans, only to be curbed by an adult with the placement of a flipper on the youngster’s head. In 1993, I (Kathleen) watched an adult female spotted dolphin that had been “babysitting” a group of youngsters keep her pectoral fin on her calf’s melon for several seconds after a particularly swift game of keep-away with several other young dolphins. Flipper-to-flipper rubs appear to function as greetings like handshakes or hugs among people.6 The situation often dictates the specific function or meaning of the flipper contact, be it a touch or a rub between individuals. Pectoral fin contact may also signal affection to another dolphin.
Individuals might use their flippers to touch or emphatically rub a body part of another dolphin. These flipper contacts are often modified by other signals, such as posture or vocalizations, to make the point even clearer. Mutual flipper rubs might be a signal to renew a friendship whereas use of a single pectoral fin by one dolphin patting a second may signify appeasement.7 The latter behavior is especially evident to human observers when the sender is an adult and the receiver a younger dolphin. Compare flipper rubs with handshakes or pats on the back in humans: the meaning varies, even if slightly, depending on the context as well as the age and sex of the participants. So, messages can be sent by a variety of methods, and for many species, actions often speak louder than words.
One thing that has become abundantly clear is that dolphins use their flippers to exchange many types of messages with peers. But could use of the flipper to share information be extended to a human being? More specifically, could pectoral fin rubs be used by a dolphin greeting a person? From 1991 until 1995, I (Kathleen) spent each summer studying the communication patterns of Atlantic spotted dolphins in The Bahamas. I returned briefly in 1997 and then, after a two-year absence, resumed research there in 2000. Although it would be hard to test or prove scientifically, I secretly wondered if the dolphins would remember me. If so, how would I know? Many dolphins that I had identified previously had aged and gained more spots; some had offspring of their own. It felt as if my family was growing up! What surprised me most, however, was how closely the older ones—and their young born during the two years that I was away—approached me. A couple of dolphins even rubbed their flippers against my body! Had they remembered me? Had the young dolphins been told about the “two-legged being (me) with the green tube” (my camera system)? We have no way to prove this or even to ask dolphins what they mean when they rub a human. But considering that dolphins use flipper rubs and other rubbing contact as greetings in certain contexts, and considering that these dolphins rubbed me when I saw them for the first time that season, a meaning of “hello” or “nice to see you” might not be far-fetched. Of course, the rubbing could also simply have been an artifact of the increased tolerance and habituation to human swimmers by newer generations of Atlantic spotted dolphins. Something to ponder on the boat ride home … or when watching the videos over and over at the lab.
Research on dolphin acoustics suggests that these animals use tonal whistles of mid- to high frequencies (or pitches) primarily when socializing.8 These whistles appear unique to dolphins, and they vary across species as well as within species across geographic locations, social groups, populations, and even individuals of different gender and age.9 Pulsed broadband tones in the form of echolocation clicks are associated more commonly with nonsocial activities, such as foraging or short-range investigation.10 Burst-pulse sounds—short broadband vocalizations—vary in intensity and encompass squawks, squeaks, moans, barks, groans, and yelps, to name a few.11 Although they are used in social contexts, these sounds have not been studied as extensively as other dolphin vocalizations.
How have we been able to learn about the sounds that dolphins produce? Have we been able to decipher why dolphins use certain sounds for particular reasons?
Dolphins have been held in captivity since the 1800s, but not until the early 1950s were scientists able to document and record sound underwater: the first hydrophones were used by David and Melba Caldwell at Marine Studios in Saint Augustine, Florida, to document dolphin whistles and clicks. We have learned much since that discovery. Although dolphins have vocal folds (homologous to our vocal cords), they are modified and probably not used in sound production.12 In the early 1990s, Ted Cranford, Mats Amundin, and Kenneth Norris used MRIs and CAT scans to study the dolphin skull and began to illustrate how dolphins might create their repertoire of sounds.13 They examined forty individuals from nineteen species of dolphins, porpoises, and other toothed whales, generating the currently accepted hypothesis that toothed whales have a “biosonar signal generator” in the nasal complex located approximately behind and below the blowhole in the head. This biosonar signal generator (or MLDB complex) consists of two structures: the dorsal bursae and the phonic lips (nicknamed “monkey lips” because they apparently resemble the lips of a chimpanzee). The passage of air over these structures creates the pulses that produce echolocation, or dolphin biosonar, which has a signal at about 120 kHz—a value significantly greater than the sound frequency a person could either make or hear. The fatty acoustic lens tissue in the melon gives dolphins a way to direct these pulsed sounds. Scientists once thought that dolphins used echolocation only to detect prey and in short-range navigation and that whistles, or frequency-modulated pure tones, were the primary vocal signal used in dolphin communication. But not all dolphins whistle, which suggests that echolocation, as well as other pulsed sounds, might also be used in communication.14
As most people know, dolphins breathe through a single blowhole. Less well known is that they have two openings in their skull, just as terrestrial mammals do. Through evolution the left nostril has become the blowhole and the right has been modified into four sets of air sacs that reside above the skull, behind the melon, and below the blowhole. Dolphins are believed to make their whistles by passing air back and forth between these sacs, which is not to be confused with the MLDB complex, where sonar is produced. If this is hard to imagine, think of a balloon that you would inflate using your lungs. Blow up the balloon but don’t tie off the end; instead, pinch the end flat and let the air escape. The resulting sound is a good imitation of a dolphin whistle!
The dolphin melon acts like a lens and helps direct the pulsed sounds that are echolocation. Dolphins receive sounds (that is, they hear) through their lower jaw, which is hollow and filled with the same fatty lipid that makes up the melon. Whistles are generated by air being passed back and forth between four sets of air sacs behind and below the blowhole.
If an animal is going to use sound to communicate, then it should be able to receive and understand the acoustic signals used. Hearing, in its most simple definition, is the detection of sound. Technically, acoustic waves are the propagation of a mechanical disturbance through a specific medium; sounds are waves, just like light, but their structure is different. Think about a thunder and lightning storm. We see the lightning before we hear the thunder (unless the storm is directly overhead), but we also feel the rumbling of the thunder as it approaches. This is because we can feel sound waves over parts of our bodies, but we use our ears to capture the sounds, which are then transported to our brain for deciphering. Even though dolphins lack external ear pinnae, they have an internal ear bone structure at least comparable to most terrestrial mammals (including humans).15 The middle ear is essentially isolated and insulated from the rest of the skull by the ecto-tympanic membrane and is connected to the skull by one small piece of cartilage.16 This isolation reduces interference from the echolocation waves produced in the cranium. The tympanic membrane (eardrum) is attached to the ecto-tympanic membrane by a narrow membrane on one end and the hammer (malleus) on the other. It has the appearance of a folded umbrella, which is very different from that of land mammals.17 The ossicles—what humans generally call the hammer, anvil, and stirrups of our middle ear—are also somewhat different in shape relative to those of terrestrial mammals, but the same general configuration exists.18 The muscles of the middle ear are greatly reduced, having been replaced by a thick collection of veins and arteries. This plexus of blood vessels is probably an adaptation for deep diving. The plexus might be inflated to reduce airspace in the middle ear cavity, thus increasing pressure to match ambient pressure when at depth.19
If the ear is more adapted as a diving mechanism and we know that acoustic signals are one of the most efficient methods of sharing information in the oceans, then what might be the most likely way for a dolphin to receive sound? Here’s a hint: although their smile is probably one of the most recognizable traits of all dolphins, it is also functional. Dolphins receive sound with their lower jaw.20 Their lower jaw is actually hollow and filled with a lipid nicknamed acoustic fat. This same acoustic fat that fills the dolphin lower jaw also resides as a sort of lens in the melon, the dolphin’s forehead. The lipid lens in the melon helps direct sounds passing from the dolphin to the environment. The lower jaw acts sort of like human outer ears to help the dolphin receive sounds and get information about the direction from which a sound originates. The overall blubber layer, which is great for warmth, stream lining, and energy stores, also insulates dolphins from being bombarded by sounds from every direction. Unlike dolphins, when we humans are in the water, we tend to “feel” the sounds more than actually hear where they come from. One reason for this is because sounds travel about four and a half times faster underwater than in air, and we are built to identify the direction of a sound source only through air. Over time, dolphins evolved to a social life in the sea; they have developed adaptations that allow them to take advantage of their environment and optimize its properties to facilitate information sharing—communication—among group members.
Why would sharing information be important to social life? As we mentioned earlier, a coordinated social life relies heavily on information sharing among individuals of a group. The ability to share information within a group requires complex social coordination that is learned at a young age. Think about our own species and how much play can resemble fighting from a distance. The behaviors of animals engaged in play or fighting are remarkably similar. Play is often characterized by mock fighting behaviors like biting, hitting, chasing, and growling or other loud, harsh sounds, but subtle cues remind those involved (as well as those observing) that the activities are not truly aggressive. Play in young animals benefits the formation of long-term social attachments; through play, the young are learning the meaning and proper use of the signals within their social structure.21 Think of puppies or dogs, kittens or cats, or your younger brothers or sisters as they play and learn what is proper etiquette within the rules of the game. I (Kathleen) have often marveled how young spotted and bottlenose dolphins always seem energized by a good game of chase or underwater keep-away. I’ve watched a group of juvenile and subadult spotted dolphins play keep-away with a sea cucumber. They seemed like children on a playground zipping to and fro with their toy. Learning a set of communication skills, or acquiring knowledge of the signals appropriate for sharing information with peers about a specific topic, will benefit each individual as he or she grows and becomes a member of the adult community. The sea cucumber likely served as a bonding tool, or toy, for the dolphins during play that helped them establish their budding friendships.
Coordinated feeding behavior is one of the most important learned skills among dolphins that requires an efficient exchange of information. What dolphins eat as their primary prey often depends on where they live: dolphins generally eat squid, octopus, shrimp, some invertebrates, and fish. The bulk of a dolphin’s diet is fish: dolphins hunt both solitary and schooling fish from within the water column, near or far from shore, from above the water surface, and deep in the ocean. Dolphins forage for prey through a variety of strategies that require coordination and communication among individuals, including hunting cooperatively or in groups, crater feeding (named for the crater depression in the sand after a dolphin pulls out a fish that was buried there), chasing fish onto mud banks and beaches, stunning fish in the shallows by whacking or kerpluncking them with their flukes, and corralling fish with bubbles.22 Beach hunting, also known as strand feeding, is one strategy employed by killer whales and bottlenose dolphins in different geographic regions. Individual members of some killer whale populations in the North Pacific, South Atlantic, and Indian Oceans will beach themselves to hunt amphibious mammal prey such as sea lions. In this method, the hunters patrol the shoreline from a moderate distance while remaining silent. They strike with speed and agility when they identify their unsuspecting prey. Adults teach this strategy to young killer whales both by example and with direction: to this end, an adult may actually toss a caught sea lion to a juvenile when class is in session. Transmission of this foraging tactic is cultural and has been documented among generations of these leviathans.23 The young orcas must practice their beach approach as well as their shimmy to get back in the water and avoid becoming truly stranded. As with many human skills acquired during youth, practice makes perfect.
When dolphins fight, there is no affectionate contact or rubbing action. They approach each other at right angles or head to head.
When dolphins play, they will often “wrestle” over each other and approach each other at oblique or odd angles, even from behind. They will also rub each other often when playing.
Another form of beach or strand feeding is practiced by bottlenose dolphins along the East Coast and in Australia. Along the muddy shores of Georgia and South Carolina, bottlenose dolphins will chase mullet onto the beach by creating a pressure wave that the fish ride and from which they leap.24 In Perth, Western Australia, however, only four adult female bottlenose dolphins and their calves from among the larger population feed in the shallows along the Cape Peron beaches.25 In contrast to the coordinated efforts of U.S. East Coast mud bank feeders, the Cape Peron beach hunters rely on the incoming tide to avoid permanent stranding and are mostly solitary in their efforts. At Cape Peron, only calves of beach hunters have exhibited this behavior, and they are also at least a year or two old when attempting their first beach hunts. These observations suggest that the calves learn this behavior from their moms.
Two more accounts of foraging bottlenose dolphins illustrate the diversity and breadth of their hunting strategies, as well as the level of coordination and apparent communication involved with these activities. Dolphins generally swallow their fish whole, usually headfirst; it was thus believed that dolphins do not share fish. Where is the exception to this rule? In 2003, Sharlene Fedorowicz and her colleagues in Costa Rica saw two bottlenose dolphins (an adult male and an adult female) sharing a fish.26 The female was accompanied by a calf, but her calf never touched the fish. Both adults were identified as part of the study population for a few years. The fish changed “hands” eleven times before it was consumed, and neither dolphin attempted to escape with the fish before the duet was complete. Although the function of this exchange is not yet fully understood, a minimum level of signal exchange between these two dolphins was required. And perhaps more—maybe the male was courting the female with a fish present? This behavior may represent a form of courtship display that we have yet to observe fully or understand. We hope one day we’ll know the answer.
Off Cedar Key, Florida, Stephanie Gazda and her colleagues examined group hunting by two groups of bottlenose dolphins that exhibited role specialization. That is, these dolphins practiced a division of labor during coordinated foraging.27 Individually identified dolphins assumed the role of “driver” while other dolphins in the group acted as a “barrier” to the fish. The driver chased fish to the barrier, and all took turns eating fish. The only other nonhuman animal for which a division of labor has been witnessed during foraging is the African lioness.28 Females coordinate their hunts with center and peripheral roles. Success during coordinated hunting is higher when each female occupies a specific role, as compared with solitary hunting strategies. But how does each dolphin (or lioness for that matter) select his or her specific role? Are the roles assigned by hierarchy or skill? Also, what signals do they use to coordinate their foraging bouts? These questions remain unanswered to human observers, but one thing is certain: these individuals must communicate intent and action with their group mates if they are to engage in a division of labor for coordinated hunting.
The social life of various species and populations of dolphins bears various similarities with other animal groups. The family Canidae comprises roughly thirty-seven species, including African wild dogs, which hunt cooperatively, as well as other canids that share food and provide care for sick pack members and dependent young.29
Most dolphins live in a fission-fusion society. What does this mean? A fission-fusion social structure is characterized by individuals who associate in small groups that change in composition and size hourly, daily, seasonally. Bottlenose dolphins are a classic example of the variety in social structure found among delphinids. Researchers have ongoing, active projects studying bottlenose dolphins intensively in Sarasota Bay, Florida; in Monkey Mia, Shark Bay, Western Australia; along the Texas and California coastlines; in Moray Firth, Scotland; in the Black Sea; in The Bahamas; and in the waters of Japan, to name only a few locations.30 Some dolphin communities, such as the populations studied in Sarasota Bay and Shark Bay, seem to be matrilineal, consisting of females and their accumulated offspring or sisters and other females. Calves within these groups will often develop stable relationships with one another over a period of years.31
The strongest bond between any two individuals for bottlenose dolphins has been confirmed as the association between mothers and their calves. Maternal investment ranges from two to four years in most studied bottlenose dolphins: the calf spends all of its time in the first year of life with mom, and occasionally with her adult female companions (often older female siblings of the calf or female siblings of the mother). Time with mom represents a period of learning and development. Calves are born with the ability to vocalize, to echolocate, and to whistle.32 Calves must, however, still learn when and for what reasons it is appropriate to use the signals in their repertoire. They can practice these signals in the relative safety of the company of their moms in their natal group. In these situations dolphins often share babysitting or “calf-sitting” duties, in which some adult mothers watch several calves while the others forage in deeper water. This environment offers a setting for calves and other juvenile dolphins to learn from one another as well as to be directed by adults in their use of vocal, behavioral, and tactile signals. Stan Kuczaj and his students at the University of Southern Mississippi provided evidence that dolphin calves learn signals or innovate new behaviors more quickly in the presence of peers, specifically other calves of similar age.33 The adult babysitters seem to oversee the activity of the calves and may intercede if a wrong signal is used, but association and interaction with similarly aged individuals, whether dolphins or humans, seems to offer a productive learning environment. The youngsters get to practice the signals that will form the foundation for all their communicative exchanges and to form social bonds that will endure a lifetime.
In the bottlenose dolphin social groups in Sarasota Bay and Shark Bay, subadult males usually leave their natal groups and form “bachelor” groups that often remain together indefinitely.34 In these two study populations, sexually mature males often form partnerships or coalitions with other males and move between the female groups primarily for the purposes of reproduction. The level of association in these male friendships rivals the strength observed in the bonds between mothers and their calves.
Killer whales are the biggest species in the family Delphinidae. Northeast Pacific resident and transient orcas are sympatric populations—that is, diverse foraging and social strategies have resulted in separate stocks.35 As a species, killer whales have a diverse diet, a strong matriarchal social structure, and acoustic behavior that includes dialects and other vocal cues that can be used to identify family pods.36 (A pod is a group of genetically related individuals. Thus, even though you often hear about dolphin pods in movies, on television, and in books, only orcas actually live in pods. Other dolphins are found in schools or, more generically, in groups.)
Dolphins, much like many primates, live in a fission-fusion society. They spend a lot of time in small groups, come together to form larger groups for foraging or socializing, and then split up into smaller groups again. Membership in groups formed before and after the big group is created can change or stay the same.
Dolphins are exceptionally tactile and are often found in physical contact with one another. Calves especially stay close to mom as they develop in their first two to three years of life.
Killer whale society and maybe even orcas’ relatedness are defined better by their vocal dialects than by their social behavior or travel associations. In this way, orcas are one of the most elegant examples of the importance of communication as a key to social structure and survival. The significance of vocal repertoire and dialect for society and culture is most easily observed in the highly stable “resident” orca groups of the northeastern Pacific.37 The basic level of their social hierarchy is the matrilineal group, which typically persists over the animals’ lifetimes—calves remain with their moms for life. The bonds among individuals of these matrilineal groups are so strong that it is unusual to see members of a pod apart from the group for more than a day. With the exception of some human populations, killer whales are the only mammals in which both genders remain with their maternal group for life. African elephant and lion females often remain with their matrilineal groups, much like many dolphin species, but the males leave the group at least occasionally, if not permanently.38
Within a matriline, the most stable level of social organization is the pod, consisting of one or more females and their offspring. Members of each resident pod share the same call repertoire and only occasionally share calls with other pods. The next level of cohesion is the clan: clans contain pods with similar vocal dialects, and it is believed that each clan originated from one pod.
Like other dolphins, killer whales produce three forms of vocalizations: clicks, whistles, and pulsed calls. In resident orcas, the vocalizations, or call types, within matrilineal groups are distinctive dialects. The calls of individuals within these groups can also be identified: each member has the same “accent,” so to speak.39 (Think of the distinctive accents of people from Boston, New York, Alabama, and Texas.) Dialects have also been confirmed in killer whales from northern Norway, and as more data are gathered, dialects will probably be found in other orca groups.40 These dialects provide information on individual and pod identity not only to other orcas but to human observers. Recognizing individuals from your family group by voice is important if you live in water with limited visibility, as do the resident Pacific Northwest killer whales. The overlapping pods of this region of the Pacific sometimes form superpods for mating and other social activities. The varied dialects allow orcas to identify family and nonfamily members during these large social gatherings. The dialects also help orcas in collaborative hunting: whistles help to coordinate activity, whereas echolocation is used primarily to locate prey.
Orcas form a matriarchal society, with all offspring remaining with mom for life. The pod contains one or two adult females and all their descendants. A clan represents pods with similar vocal dialects. The killer whale pods in the Pacific Northwest have been studied for several decades, and some researchers can recognize the pods by their dialects.
Resident killer whales rely heavily on their different calls to share information when engaged in a variety of behavioral contexts. In the Pacific Northwest, the transient population of killer whales has a range that extends farther offshore and much farther south than resident pods. These transients live in smaller groups and partake in a very different set of foraging tactics.41 Vocalizations, as with other dolphins, are important to transient orca communication, but differences exist. Transients have adapted to more silent hunting practices and developed other methods for information sharing while pursuing their prey. This makes sense—they are hunting mammals with similar hearing and vocal ranges. Using echolocation or other vocal cues to stalk their prey would be akin to announcing their intent and presence: hunger would likely follow. As separate subspecies, resident and transient orcas have each learned to adapt and maximize the resources of their niches.
When killer whale pods join, they engage in vocal and behavioral greeting ceremonies. African elephants have similar practices. When feeding, individual elephants will range over large distances. When they later prepare to regroup, individuals will signal vocally with a rumble and a special posture.42 When in visual range but still at a distance from group members, individuals may raise their heads, lift and spread their ears, tuck their chins, and then rumble loudly while flapping their ears. Individual elephants or groups meeting may first raise their trunks in the air to smell or continue rumbling, head lifting, and ear spreading. They may press heads together and gently click or even intertwine tusks, sometimes while rumbling. This tusk entwining varies from tusk-to-tusk battle observed when males, especially those in musth, are competing.43 I (Toni) have observed such elaborate greeting ceremonies firsthand in two very different environments: orcas in the waters near my home in the Pacific Northwest and elephants in Africa. Some of the elephant sounds I heard during a greeting sounded as if the earth was purring like a giant cat. One of the things that struck me the most was that I could feel some of their low-frequency sounds. I felt what prompted Katy Payne to investigate their sounds. I can’t imagine what people thought when feeling these sounds without knowing they came from elephants. Perhaps they thought there was an earthquake?
Mutual flipper rubbing between dolphins is usually a tactile greeting behavior.
Although the greeting ceremonies among killer whales and elephants represent more vocal and postural salutations between individuals and groups, touch is used as a greeting in many species, as discussed previously. I (Kathleen) have observed flipper-to-flipper rubs in spotted and bottlenose dolphins used as greetings between individuals that have been apart in time or space, as well as possibly to greet human swimmers who have been absent for a few seasons. I believe that dolphins readily recognize peers, and maybe even individuals from other species, though data on the latter are currently lacking. I have seen adult females both in The Bahamas and around Mikura Island swim toward one another without a sound to exchange pectoral fin–to–pectoral fin rubs. This greeting always reminds me of the handshakes or hugs exchanged by people outside the baggage claim area in airports. Touch is a great reassurance, a reminder of a friendly relationship between individuals, no matter the species.
The method scientists use to identify distinct whistles is spectrographic analysis. A spectrogram is a picture of the sound we hear. This picture is actually a graph of sound frequency versus time. The plot of each whistle forms a line that is either straight or curved. Whistles are narrow-band, frequency-modulated sounds that usually last from a tenth of a second to three seconds with fundamental frequencies that range from 5 to 20 kHz.44 A whistle’s energy concentrates in a thin band on a spectrogram, forming a distinctive pattern called the whistle contour. This contour is what has been described as distinctly characteristic for specific dolphin whistles. In the scientific community, there is much controversy about the nature and function of dolphin whistles.
Dolphins produce two broad categories of sound: pulsed or click sounds and whistles. This spectrogram is a visual picture of a dolphin whistle. Time is on the x-axis and frequency is on the y-axis. This whistle has harmonics and several inflection points or loops and was produced by an Atlantic spotted dolphin in The Bahamas.
In the 1950s, Carl Essapian and David and Melba Caldwell made the first recordings of dolphin whistles, which led them to suggest that individual bottlenose dolphins might produce distinctive whistles.45 The Caldwells termed these calls “signature whistles,” which, by definition, represent 90 to 100 percent of a dolphin’s vocal repertoire and were easily discernible from the signature whistles of other dolphins.46 At about the same time, with different animals, William Dreher and William Evans reported that dolphins shared a large repertoire of signals, with particular whistles used in specific situations or to convey different emotional states.47 Intriguingly, the production of some whistle types was attributed to all four species examined by Dreher and Evans, whereas other whistle types were produced exclusively by a single species. This is the crux of the scientific debate over signature whistles: Is a dolphin’s vocal repertoire made of fewer specific and individually distinct whistles or of a larger set of more varied whistles? Two competing hypotheses feed this debate.
The signature whistle hypothesis postulates that signature whistles remain distinguishable and stable over years for each individual.48 This hypothesis also stipulates that variation in some acoustic features in the whistle, such as duration, intensity, and number of whistles produced per minute, would change in different behavioral contexts and so provide information other than individual identity. Still, the main information conveyed by each whistle is individual identity. Spectrographic analysis is used almost universally in the study of animal sounds: elephants, birds, whales, dolphins, and even humans. Dolphins produce additional whistles in their repertoire that are not signatures: these whistles appear in low numbers and have been called “aberrant.”
In contrast, the whistle repertoire hypothesis stipulates that dolphins share a large repertoire of whistles with other individuals. This hypothesis advocates that information concerning individual recognition of an animal could be represented in subtle differences in the acoustic features of each whistle contour, similar to the voice cues found in primates. Researchers Brenda McCowan and Diana Reiss argue that by calling whistles that are different from signature whistles “aberrant” or variant, previous studies may have suppressed the function or position of these whistles within the dolphin vocal repertoire.49
Both hypotheses are based on results from work conducted on captive dolphins, though both also have support from observations of dolphins in the wild. In Monkey Mia, vocalizations exchanged within mother-calf pairs were recorded when they were separated.50 The calves seldom produced whistles when in contact with their mothers but whistled often when apart from mom. The whistles were individually distinct. In a study in Sarasota conducted for more than fourteen years, the vocal exchanges between mothers and their calves were recorded. One major difference between this study and the one conducted in Australia is that the dolphins in Florida are temporarily held with nets in shallow water.51 During the time span of the study, the signature whistles of individual dolphins did not change. Even calves, recorded as young as one or two years old, used stable signature whistles. Although these studies discovered important aspects in the communicative aspects of whistles, they share a major drawback. They did not record dolphins during complex social interactions. Instead, the calves produced whistles while leaving or returning to their mothers or in isolation from peers. Dolphin society is an intricate, fluid assembly of fission-fusion interactions. To record a complete repertoire of dolphin whistles, one would need to record them in a variety of social contexts. In all animal communication systems, individuals are more likely to convey messages, to share information or probe for it, when in the presence of other individuals. Therefore, these studies likely presented a small part of these dolphins’ normal whistle repertoires.
The vocal data from spotted and bottlenose dolphins that I (Kathleen) have collected over the years at first led me to reject the signature whistle hypothesis. With my recording system, I am able to match sounds to individual dolphins and their actions for about 40 percent of all my data. At all of my field sites, I have never had the same number of distinct vocalizations as there are number of dolphins. And besides, why would dolphins, accepted as highly evolved and intelligent beings, swim around all the time whistling only their name? The data I gathered, from socially interacting groups from underwater, with dolphins almost always in visual range of peers, showed no support for individually distinct whistles per identified dolphin. That is, I recorded about ten categories of whistle contour patterns that several dolphins produced. It would be safe to say that I was solidly in support of the whistle repertoire hypothesis for about a dozen years. Then I began studying dolphins in captivity along with my work on wild populations. I chatted with trainers about the distinct whistles emitted by specific dolphins that the trainers readily recognized. I heard these whistles myself. I began to rethink my archive of data and my interpretation in light of my recent observations. I now believe the hypothesis proposed by Vincent Janik and Peter Slater, which suggests that individually distinct whistles are likely used to maintain group cohesion or contact among individuals separated by distance.52 That is, dolphins out of sight of friends or group members use a specific whistle (defined by us with a spectrographic contour pattern) to remind their buddies that they are nearby or that they want to regroup. My data then made sense: signatures or individually distinct whistles would be hugely underrepresented in my data, since the dolphins that I observe are always in view of their peers.
Reciprocally altruistic behaviors between nonrelated animals require that individuals be able to recognize one another individually. This is particularly important when all animals within a given group are not genetically related. The ability to recognize individuals in large social groups facilitates cooperative alliances and other associations.53 Individually distinct whistles could be very useful for maintaining individual bonds and social hierarchies within the fission-fusion society characteristic of many dolphin species.
Vocal learning—the ability to modify one’s vocalizations in response to auditory experience—has been confirmed in only a few mammal species, for example, humans, chimps, elephants, and dolphins.54 A flexible and open communication system is enabled by vocal learning; animals may also learn to imitate signals that are not species typical.55 Dolphins can imitate a trainer’s whistle, and an African elephant demonstrated an ability to imitate truck noises.56 Vocal learning is an evolutionary response to maintaining relationships in a fluid fission-fusion society. Learning to imitate peers is a communication tool for the maintenance of individual-specific bonds. In many instances, vocal learning is also considered evidence of higher cognitive processing.
For many species, nonvocal communication is an important component of information exchange. Visual displays or signals include body postures, coloration patterns, and elaborate sequences of behaviors—anything that can be seen. Visual signals can indicate the species or individual identity, age, sex, or reproductive status. Visual cues such as postures or behaviors are likely to signal intent and demeanor of a sender, as well as provide insight to the meaning concluded by a receiver. Land mammals exchange much information through subtle or overt kinesic (gesture or movement) expressions, including changes in facial expression (a dog’s snarl), irregularities in respiration, and overall body movement. When fighting, many animals have the ability to make themselves seem larger. Elephants will flare out and flap their ears when agitated.57 Bears rear up when attacking or defending their young. Birds fluff out their feathers and cats fluff their fur. Dolphins flare their pectoral fins while producing bubbles during a fight. In 1994, I (Kathleen) observed a group of spotted dolphins fighting in small gangs: groups of three to four individuals were going head to head, vocalizing loudly, ramming and hitting one another, and producing large amounts of bubbles (streams, trails, and clouds). I have no idea what they were fighting about. The dolphins that were vertical and head up below another group produced more bubbles and flared their pectoral fins more than the dolphins above them. Based on this scene and many other observations, I believe dolphins engage in the art of intimidation. If you can bluff another individual away with bluster or bubbles and flipper flaring, then you might avoid the more energy-consuming actions of a true fight. And you stand a better chance of not getting injured!
A group of spotted dolphins is tightly formed and circled against a single bottlenose dolphin who tried to infiltrate the group … possibly for mating or maybe for play.
The spotted dolphins are successful in fending off the bottlenose dolphin in this instance.
Dolphins also use synchronous behavior to signal to peers and opponents, depending on the context. Some male bottlenose dolphins form friendships that last a lifetime; they are rarely, if ever, seen apart.58 These male pairs may work with other male pairs to herd females or compete for access to female dolphins for mating. Within each pair, the male dolphins often engage in highly synchronous actions, often surfacing to breathe, leaping, diving deep, or traveling in perfect unison. This synchronous behavior is a form of communication, not only to each member of the pair but also to potential opponents or even to the pursued female. The males are using this nonvocal behavior to illustrate their bond and camaraderie. Their synchrony showcases their ability to coordinate closely and work together toward a goal. Competing male dolphins, as well as the female being pursued, know that the synchronous pair is a solid team. In this way, by their harmonized movements, the male dolphin pair is honestly signaling their intent, either toward the female or toward the competition.
Communication between individuals is not always honest and forthright, and the transmission of misleading information is used to deceive and manipulate the behavior of others. Deception is observed in a variety of land animals, including vervet monkeys, great tits, and chimpanzees.59 Human beings fib, fabricate, and tell lies to further their cause. Think of the sweetly smiling boy who asks for dessert without having finished his peas, hiding them under the last scoop of mashed potatoes. Why else would we learn at a young age to lie about the source of the spilt milk or blame the dog for the dirt tracks on the living room carpet? Given the highly developed communication systems of dolphins, it is likely that they also employ deceptive signals. Because of the relative lack of detailed studies on dolphin communication, as compared with terrestrial mammals, however, it is not surprising that deception among dolphins has not yet been conclusively demonstrated.
Evolution may have contributed in a variety of ways to geographic variation in whistle characteristics within and among dolphin species. Acoustic variation in habitats affecting sound transmission properties may influence the vocal qualities of some dolphins. Over time, habitat differences can affect the genes of populations or species so that they are able to produce different types of vocalizations. The distinct dialect of each resident Pacific Northwest killer whale pod cannot be attributed to reproductive isolation, since these pods not only share much of the same habitat but also socialize frequently. The impact of geographic distribution and cultural selection has also been explored in the freshwater and marine subspecies of the tuxuci dolphins.60 In this case, some individuals within the two subspecies inhabit different ecological niches, whereas others overlap. In this and other dolphin species, habitat and genetic differences may always be an influence, but as in the case of the resident orcas of the Pacific Northwest, variation in vocalization, as well as other behaviors, are more likely attributable to social learning and cultural transmission across generations.
