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DOLPHIN MYSTERIES Unlocking the Secrets of Communication
By KATHLEEN M. DUDZINSKI TONI FROHOFF
YALE UNIVERSITY PRESS Copyright © 2008 Kathleen M. Dudzinski and Toni Frohoff
All right reserved.
Chapter One A Dolphin's Life
They say the sea is cold, but the sea contains the hottest blood of all. D. H. LAWRENCE, "Whales Weep Not!"
The sea churns with foam. From the surface emerge shimmering bodies as far as the eye can see. They are dolphins, leaping above the water, visiting our world for a moment before disappearing from view. Again and again they surface-thousands of sleek bodies pushing toward a destination we do not know....
This was my first view of dolphins in the wild. I was a student intern on a whale-watching boat off Cape Ann, Massachusetts. The sight of so many dolphins moving in unison was breathtaking. I almost forgot to record data, but I recovered and thus began documenting dolphin behavior for what will probably be a lifetime.-Kathleen
Common dolphins can travel in schools of thousands, even tens of thousands. These ocean mammals, true to their name, are found throughout the world's oceans, and people often see them in vast numbers. Yet our view from above the water's surface does not allow us to see or hear them in the three-dimensional ocean world in which they live.
When we see dolphins, it is typicallylike this: from a boat or from land, dolphins appear for a second or two, and the rest is left to our imagination. This can be exasperating for researchers, especially because dolphins exhibit what may be the most complex, unique, and intriguing communication systems of all animals. But, when we go beneath the ocean surface, where dolphins live, we can find out how they live, how they communicate and interact with others, and maybe even more about who they are as individuals. As we delve into the realm of dolphins, we learn that they are not just members of a group but unique individuals, each expressing a kaleidoscope of physical and behavioral characteristics.
Imagine for a moment that an alien scientist is examining an aerial view of people on a busy street sidewalk. The people all appear to look and act pretty much the same from this vantage point. Only if the alien approached and followed individuals would each person's physical and behavioral discreteness emerge. And if this observer did not understand our language or could not hear or see in the same frequency range as us, an understanding of our world would be even farther out of reach. As aliens to a fully aquatic lifestyle, we dolphin researchers are in a similar situation. It is not always easy to admit how little we know about dolphin life; then again, that is what keeps our work so perpetually inviting.
Dolphins live in an environment that is foreign, even hostile, to humans, making their study and collection of data on their activity difficult at best. What keeps us coming back for more is not only the quest to understand the puzzle of dolphin behavior and communication but the excitement of glimpsing the world of another social being and the possibility of understanding another type of mind.
We have both attempted to gain a broader and more representative picture of how dolphins live in their underwater world. Our research represents two sides of the same coin. Kathleen investigates how dolphins interact with one another, and Toni focuses on how they interact with human swimmers, divers, and boaters. Our work requires us to spend extensive periods in the water with dolphins, observing their actions using underwater video cameras, still cameras, and writing slates. Although we focus on slightly different topics, our observations complement each other. This is true whether we have observed different species or the same dolphins in the same geographic area.
In The Bahamas, for example, we have both studied free-ranging Atlantic spotted dolphins, which travel in much smaller groups than their "common" cousins. From above the water, we see them swimming side by side as they surface to breathe. The underwater scene, however, tells a different story. These aquatic athletes sometimes swim frantically around one another, coming together to surface and breathe in unison, only again to split off from one another to resume their underwater speed ballet. Tracking the same individuals underwater often reveals a scattered, zigzag pattern, which requires us to follow the same pattern with our eyes as well as our swimming! Dolphins are excellent mimics and move in effortless synchrony. It is hard to keep pace with them. If a dolphin does not want to be near you anymore, she or he can vanish in an instant. Toni has observed dolphins swimming with humans in a manner similar to the way they swim with one another. When a dolphin is patient, the human and dolphin movements can be almost perfectly synchronous except a swimmer's snorkel is breaking through the water's surface alongside a dolphin's blowhole. An interesting observation in this regard is that dolphins often seem to "accommodate" some human swimmers by letting the swimmers set the pace, even when the swimmers are much slower and less agile, and need air much more often. Similarly, Kathleen has noticed that dolphin mothers often accommodate their calves in a similar manner. The calves need to stay near the surface longer because they surface more often than mom to breathe. As calves mature, they develop the physique to dive deeper and to expel and inhale more air at the surface with each breath. But until they can do this, mothers often stay with their calves near the surface.
By merging our views from above and below the ocean surface, we forge the most complete picture of dolphin life. Looking at how they interact with humans and other species helps us understand how they communicate. Dolphins are highly social animals. They often care lovingly for their young for years and assist peers in distress in a manner exemplary even by human standards. Of course, there are exceptions: Kathleen has observed wild Indo-Pacific bottlenose dolphin moms who would not win any parenting awards for nurturing, attentive behavior. These mothers even had a higher calf mortality rate compared with other females in the group. The complexity of dolphin society is evident in how they fight with one another, as well as how they play, mate, feed, rest, and communicate.
Dolphins have long fascinated humans and are the focus of myths and fables in many cultures. Yet modern research has shown that many of these fantastical-sounding tales could in fact be true. And the complexity of dolphin society makes the facts even more fascinating than the myths. Some aspects of dolphin life are amazingly similar to that of other social animals-both aquatic and terrestrial, wild and domesticated. Observing them underwater allows us, as terrestrial social animals, to perceive their world through our senses. We eavesdrop on their lives and compare and contrast what we find to other social species, including humans. It is a moment where land and sea mammals meet ... if only for a short time.
With their modified anatomy and streamlined form, dolphins are supremely adapted to life in the sea. Like us, they are mammals: they breathe air, are warm-blooded, suckle their young, and have hair before birth. But all of these things occur differently for dolphins than they do for land mammals. Dolphins are cetaceans, members of the order Cetacea. The cetaceans-whales, dolphins, and porpoises-are the most highly evolved, fully aquatic marine mammals, and make up 2 percent of the 4,600 living mammal species. Dolphins belong to the suborder Odontoceti, or "toothed" cetaceans. Toothed whales are divided into ten families grouped into three "superfamilies": Delphinoidea, or oceanic dolphins, porpoises, and monodontids such as the beluga whale; Ziphoidea, or beaked whales; and Physeteroidea, or sperm, pygmy sperm, and dwarf sperm whales. The other suborder of cetaceans, Mysticeti, comprises eleven species of whales which have baleen plates instead of teeth. Toothed whales also differ from baleen whales in having a single (instead of a double) blowhole, a highly specialized echolocation system, and a pronounced forehead, or melon.
Toothed whales make up the vast majority of cetaceans. Approximately seventy-one diverse species range from the relatively tiny vaquita, or Gulf of California harbor porpoise, which weighs in at about 120 pounds (about 50 kg) and is roughly 5 feet (about 1.5 m) long, to the well-known bottlenose dolphin, white beluga whale, and magnificent killer whale (the largest dolphin) on up to the largest toothed whale, the sperm whale, which can reach 55 feet (18 m) in length. The terms porpoise, whale, and dolphin are often used interchangeably, but size (specifically length) is the criterion anatomists have generally used to apply the common name whale. Porpoises, members of the family Phocoenidae, differ from dolphins in several characteristics. Typically smaller, they also lack a pronounced rostrum (beak) and have shorter, spade-shaped teeth as opposed to dolphins' more conical, pointy teeth. (Scientific names of species mentioned in the text are listed at the back of the book.)
Dolphins of the family Delphinidae are found in all oceans, most seas, and some bays around the globe. Most species have a falcate (sickle-shaped) dorsal fin, cone-shaped homodont teeth, a pronounced beak or rostrum, and a gregarious social structure. They range in size from Hector's dolphin, about 4.5 feet (1.3 m) long, to the killer whale, about 30 feet (about 10 m) long. Dolphins are found in almost every aquatic habitat on the planet-from coastal to deep-water pelagic ocean zones and from fresh to marine environs. Of the thirty-three species of oceanic dolphins, the best-known and most studied is the bottlenose dolphin (think of "Flipper," of television fame). Bottlenose dolphins comprise the majority of captive dolphins in aquariums and are the species most often sighted along coastlines.
As social mammals, dolphins and humans share many traits. We are both highly sociable and communicative, predatory, and intelligent, and we exhibit a variety of complex social relationships. Similarly, the cognitive abilities of dolphins are highly advanced. For example, dolphins can recognize themselves in mirrors; only humans, some of the great apes, and elephants have been demonstrated to share this ability with dolphins. In other words, although humans and dolphins lack a common ancestor, they have evolved similar cognitive abilities, possibly for comparable social or communicative reasons.
There is growing evidence that cetaceans have culture, similar to that observed in humans and other terrestrial (such as chimpanzees and elephants) and avian (such as parrots, crows, and ravens) species. The complex vocalizations and behaviors studied in different killer whale populations are evidence of distinct orca cultures. A form of cultural coevolution has also likely occurred between dolphins and humans in some regions of the world. For example, scientists have documented cooperative fishing on several continents between indigenous peoples and dolphins that appears to have developed over time across many dolphin and human generations.
In an unexpected reversal of the typical path that humans and other terrestrial-animals followed, dolphins returned from land to the sea about fifty-five million years ago. There are numerous hypotheses why cetaceans resumed an aquatic lifestyle. The most widely accepted are that the ancestors of modern whales, dolphins, and porpoises returned to water to take advantage of an untapped ecological niche, to use and more readily find a prey resource not being exploited by other species, and to have access to another food source without competition from other land dwellers.
To get a sense of when and how dolphins obtained their unique and fascinating communication and related physiological systems, we must look far back in time. The cetacean branch of the tree of life starts out about fifty-five million years ago, when the ancestors of today's dolphins returned to the sea. From fifty-five to thirty-five million years ago, all ancient cetaceans are classified as Archaeocetes; at about thirty-five million years ago, the Mysticetes and Odontocetes-the two modern suborders of whales-first appeared. If you traveled back in time fifty-five million years, you would not recognize those early cetaceans as being similar to their modern relatives. Rather, the proto-cetaceans were on a genetic trajectory that would take them, over fifty-five million years, to the species we recognize today. In fact, current theory suggests that one of the modern dolphin's ancient ancestors might have looked like a cross between a modern wolf, a cow, and maybe an alligator. Dolphins have had their current torpedolike, streamlined shape for about five million years. It's hard to imagine this, considering that modern human beings have been around for only about two hundred thousand years. Perhaps this extensive time for adaptation to the sea is one reason why dolphins have developed such a sophisticated system for sharing information-that is, communication.
Of the six families of Archaeocetes, two were the Pakicetidae and Ambulocetidae. The pakicetids, the oldest members of the lineage, were probably more semiaquatic than fully aquatic and had hind limbs that were close to fully intact. The ambulocetids, the second oldest family, also had hind limbs that were much more than "limb buds," but they were probably more aquatic than the pakicetids. The hind limbs of ambulocetids seem to be modified for an aquatic existence. As you move from fifty-five to thirty-five million years ago, and from pakicetids and ambulocetids through the other four families of Archaeocetes, there is increased reduction of the hind limbs and a more fully aquatic lifestyle. Over time, about nine million years, these large feet became permanent flippers called a fluke, or tail, that was (and is) used to propel cetaceans through the water. The basilosaurids and dorudontids (not dinosaurs, though the names sound like it), now extinct, are the oldest ancestors of cetaceans to show solid evidence of fluke swimming. Loss of hind limbs did not occur overnight but was a gradual progression as these animals adapted to an aquatic way of life; reduction of the hind limbs matched whales' and dolphins' need for functional locomotion in the water.
Anatomical streamlining for life in the sea included other modifications to the evolving dolphin body plan. Most mammals have two joints in the thumb (if present) and three in each of the fingers. Dolphins have several elongated digits per finger, even though the external view of their "fingers" more closely resembles a mitten. Imagine your hand in a mitten, but place your thumb inside with all the fingers, so that your mitten is more of a "mitt." A dolphin's flipper is homologous to the typical mammalian forelimb, for example to the human arm and hand, but it is covered by a webbing of blubber and skin that helps it function as a paddle to assist with steering through the water. Evolution has also imparted cetaceans with an elongated, or telescoping, skull, as well as a skull that meets the spine at 180 degrees, unlike the 90 degrees of most terrestrial mammals. As the skull migrated from a right-angle connection, the cranial bones elongated, shifted, and migrated to different positions: for example, the nares (nasal openings) are now atop the skull, as opposed to in front of the skull, and act as a built-in snorkel. The dolphin's torpedolike shape reduces drag when swimming and indirectly helps reduce heat loss. In addition, modern dolphins show no distinction between the vertebrae of their lower spine, specifically the lumbar, sacral, and caudal vertebrae. They have significantly more vertebrae than most other mammals, which assist with trunk-generated, or axial, propulsion. This is a stark contrast to most mammals and is actually much more comparable to that of a snake.
Molecular DNA studies confirm that the cetaceans' closest living relative is the hippopotamus. Let's build some evolutionary perspective: think about hippos and their amphibious way of life. The hippo skull exhibits many traits in common with cetaceans: telescoping, upward positioned nostrils with flaps and a blubber layer under the chin for conducting sound. Hippos can produce and receive sounds amphibiously, that is, both above and below the water's surface. The hippo typically situates its ears, eyes, and nostrils above the water's surface, keeping its mouth and throat underwater. Researcher William Barklow distinguished nine categories of hippo sounds that were broadcast simultaneously in air and water. Behavioral responses to other hippos and to playback experiments suggest that these social animals react to both the underwater and the in-air components of amphibious calls. They probably use sound to mark their territories and to mediate social confrontation. The ability of each hippo to know the location and concentration of other hippos in an area probably facilitates efficient grazing and use of pools. A better understanding of how hippos use their sounds to coordinate social activity might provide insight into the mechanisms by which acoustic communication evolved in their modern-day oceangoing cousins.
Excerpted from DOLPHIN MYSTERIES by KATHLEEN M. DUDZINSKI TONI FROHOFF Copyright © 2008 by Kathleen M. Dudzinski and Toni Frohoff. Excerpted by permission.
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