sábado, 27 de octubre de 2007

Culture of the Sea

Culture of the Sea

Whales and dolphins strut their social stuff for scientists

Bruce Bower

On a November day 9 years ago, Christophe Guinet and his coworkers stood transfixed on the beach of an isolated island in the southern Indian Ocean. They watched as a killer whale and her 5-to-6-year-old female calf, cruising a short way offshore, abruptly stopped and together turned to face an elephant seal pup moving slowly in shallow water.


Guinet, a zoologist at the National Center of Scientific Research in Villiers en Bois, France, trained a video camera on the animals and recorded the ensuing scene.

With a determined flip of the tail, the calf moved toward the young seal. The older whale followed right behind, giving her offspring a push. With deadly precision, the calf clamped her jaws around the startled pup. Meanwhile, the mother moved closer to shore, preventing the youngster from going in too far and stranding herself on the beach.

Prey firmly in mouth, the whale calf laboriously turned around. She arched her back, flapped her flippers, and dragged her belly through the soggy sand. Her attentive mother then gave her a push out to deeper waters.

Over four seasons of field work on the island not far from Antarctica, Guinet had observed the same calf or another young killer whale on numerous occasions almost stranding itself on the beach and struggling back to sea. Their mothers and adult female relatives had kept a close watch on them and swum to their aid when they got stuck. On a few occasions, one or the other of the two calves had also followed as the mother attacked seal pups near the shore.

Finally, however, Guinet felt that he had witnessed a developmental milestone. After extended observation and practice, a calf had nabbed a seal largely on its own.

This confirmed his suspicion that the whales' dangerous practice of intentionally entering shallow water in search of prey reflects neither a blind instinct nor the trial-and-error discoveries of one creature at a time. Instead, female killer whales take their offspring under their fins, so to speak, and spend years showing them how to hunt seals according to local custom.

Prior to Guinet's work, an Argentinian research team published a report describing female killer whales that tutored their offspring in seal hunting.

"I'm convinced that killer whales transfer group knowledge socially through teaching and apprenticeship," Guinet says.

His killer whale observation, published in 1995, and the Argentinian report were among the first in a rapidly growing body of research that supports the existence of cultural traditions among whales and dolphins. These practices include social learning, which researchers define as adopting behaviors from others in the group. This line of research challenges the traditional view of culture as a uniquely human pursuit.

Even if evidence for obvious teaching remains rare, most scientists who study whales and dolphins in the wild agree that these creatures live in social groups that somehow transmit learned behavior from one generation to the next. The same cultural capacity may hold for wild chimpanzees, which live in groups that pass on distinctive forms of tool use and social grooming (SN: 6/19/99, p. 388).

"I think we'll find cultural transmission in many animals that are capable of social learning," says biologist and dolphin researcher Vincent M. Janik of Woods Hole (Mass.) Oceanographic Institution.

Making waves

Whales and dolphins, known collectively with porpoises as cetaceans, have begun to make waves with their penchant for learning from each other. Cetacean researchers presented their latest findings in August at a Chicago symposium on animal social complexity and intelligence. Luke Rendell and Hal Whitehead of Dalhousie University in Halifax, Nova Scotia, will publish a synthesis of cetacean research in an upcoming Behavioral and Brain Sciences.


Carrying a harbor seal carcass after a successful hunting foray, a transient killer whale cruises through the Pacific Ocean near Canada.
Robin W. Baird

The Dalhousie biologists portray the four best-studied cetacean species—the bottlenose dolphin, the killer whale, the sperm whale, and the humpback whale—as generators of group-based, cultural systems of communication, feeding, mating, and raising their young.

Still, the concept of culture is a moving target that scientists can't seem to agree on. Broad definitions emphasize the acquisition of behaviors by succeeding generations through social learning of any kind, such as adopting an activity after seeing it performed many times by many different individuals. Strict definitions focus on traditional behaviors cultivated solely through teaching or one animal imitating another.

Cetacean evidence generally meets the broad definition of culture and, in some instances, satisfies the strict criteria, Rendell and Whitehead say. For instance, male humpback whales in breeding populations from Hawaii to Mexico produce nearly identical sequences of vocalizations, or songs, at any given time, and their songs change from year to year. An as-yet-unknown means of learning enables humpback whales to keep singing in unison despite the changes, the researchers argue. The humpbacks' song learning and sharing stand as cultural achievements in the broad sense, the scientists hold.

Innovative feeding methods also spread rapidly within humpback groups. When first studied in 1991, members of a whale population commonly enveloped schools of fish in clouds of bubbles by exhaling underwater; they then gulped down the trapped prey. At the same time, a few individuals took a different approach to wrapping fish in bubbles. Each of these innovators would slam its massive tail flukes onto the water just before diving for a snack.

Over the next 9 years, many other whales in the population, and especially juveniles just coming into their own as independent feeders, adopted the tail-slam maneuver, reported a team led by Mason Weinrich of the Whale Center of New England in Gloucester, Mass.

This trend likely depended on imitation, say Rendell and Whitehead.

Like other cetaceans, fluke-flopping whales appear ill suited for one aspect of human culture: tool use. However, an intriguing example of simple tool use may occur among bottlenose dolphins in Shark Bay, Australia. In a group of more than 60 of these animals, 5 adult females regularly carry sponges in their mouths as they search for food, perhaps to scoop prey out of hiding places on the sea floor, says psychologist Janet Mann of Georgetown University in Washington, D.C.

These devout sponge carriers forage alone, as do several of their juvenile daughters who also carry sponges.

Other female dolphins at Shark Bay only occasionally carry sponges, according to Mann. These females usually forage in groups that don't use sponges.

Male dolphins at Shark Bay haven't been observed carrying sponges. These dolphins generally gather food with one or two compatriots.

Distinct populations

Cultural practices stand out among killer whales that live in the Pacific Ocean around Vancouver Island, off the coast of Canada and Washington State, according to Rendell and Whitehead. There, whales of a single species operate in two culturally distinct populations.


A dolphin mother nurses her calf in Shark Bay, Australia. Calves there nurse for 3 to 6 years.
Janet Mann

Resident pods, which each contain 10 to 25 animals, are organized around sets of closely related females. Members of these pods primarily eat salmon and other fish. Over more than 20 years of research, scientists have yet to observe a killer whale moving from one resident pod to another.

In contrast, transient pods of these killer whales each consists of three to six whales. Members of these pods are often not close relatives, and some of the whales occasionally travel with other transient groups. Transients, who appear to be more typical of killer whales in other parts of the world, prefer a diet of seals and other marine mammals.

Vocalizing may provide an important avenue for cultural expression among the resident killer whales. Each of their pods uses its own vocal dialect, according to analyses of underwater recordings directed by biologist John K.B. Ford of the University of British Columbia in Vancouver. A single pod shares a set of between 7 and 17 discrete calls emitted by all of its members, Ford's team reported in 1991. These vocal dialects persist for at least six generations of killer whales.

Some pods share parts of their vocal dialects, thus creating what Ford refers to as vocal clans. Pods in the same vocal clan don't necessarily mingle with each other more than they do with pods from different clans, members of Ford's group reported at the Chicago symposium.

However, vocal clans tend to consist of pods that contain some closely related adult females, the researchers say. Killer whales may minimize inbreeding by avoiding potential mates who use a dialect similar to their own, the researchers theorize.

Sperm whales, like killer whales, display dialects, Whitehead says. Each group of females emits a typical pattern, or coda, of 3 to 12 clicks, which partially overlaps with the codas of neighboring groups.

Researchers have recorded instances in which two female sperm whales from different pods jointly modify their codas into identical click patterns, in a kind of vocal duet. Sperm whales may learn to match codas in this way as a sign of friendliness, Whitehead proposes.

However, definitive experiments confirming that whales learn to imitate codas or other behaviors will probably never be conducted, he notes. Such demonstrations would require raising and studying groups of the huge animals in captivity.

Compelling examples

The most compelling examples of imitation in cetaceans come from research on dolphins. "Captive dolphins are fantastic imitators of human sounds," says biologist Peter L. Tyack of Woods Hole Oceanographic Institution. These animals also accurately reproduce patterns of tones within seconds of hearing them.


Like her mother, a 14-year-old female dolphin at Shark Bay carries a sponge, apparently while foraging for food. Researchers have seen her engage in this behavior since she was 1 1/2 years old.
Janet Mann

In the wild, it's now clear that bottlenose dolphins frequently imitate the learned whistles of other members of their particular social group, Woods Hole's Janik reports in the Aug. 25 Science. In underwater settings where the field of vision is typically limited, so-called whistle matching enables dolphins to address each other from a distance, Janik suggests. An individual dolphin might echo another's call as a friendly greeting in some situations and as a hostile warning in others.

Janik used underwater microphones to record the vocalizations of dolphins that periodically gather off the coast of Scotland. During 7 different days, he recorded 39 instances in which the same whistle was emitted by two dolphins within 3 seconds. Whistle matching occurred over distances of up to one-third mile and usually in the presence of 10 or more dolphins.

Whistle matching adds to the impressive mental skills exhibited by bottlenose dolphins, Janik says.

In the Feb. 1999 Animal Learning & Behavior, Louis Herman of the University of Hawaii in Honolulu, who has directed research on these abilities, summarized the evidence on the intellectual feats of captive dolphins. For instance, with training, captive dolphins readily apply learned rules to new situations, grasp abstract concepts, and understand an artificial, grammar-based language.

Still, researchers haven't observed any examples of one dolphin teaching another any behavior, such as whistle matching, Janik remarks. He regards the isolated observations of alleged instruction in seal-hunting techniques among killer whales with skepticism.

"Something fascinating is going on with killer whales, but I don't know if it's teaching," comments psychologist Bennett G. Galef of McMaster University in Hamilton, Ont., who has long criticized reports of cultural behavior in chimps.

Rendell and Whitehead, in contrast, accept Guinet's conclusion that female killer whales teach their young how to hunt seals.

Cultural lives

Researchers have described 17 cetacean behaviors that may be cultural, according to Rendell and Whitehead's tally. The four best-studied cetacean species possess biological attributes that prime them for cultural lives, the researchers propose. These traits include long life spans (60 to 90 years), advanced mental abilities, and prolonged periods of rearing young.

What's more, these animals operate in underwater environments that often undergo rapid and substantial changes, Rendell and Whitehead say. Cultural learning may increase the chances of a species' survival in changeable settings.

Whitehead further argues that the spread of cultural traits in some whale species has altered their genetic evolution. Mitochondrial DNA samples from killer and sperm whales contain far fewer random changes and rearrangements than comparable genetic samples from many other cetacean species, he reported 2 years ago.

Killer and sperm whales live in groups headed by related females who possess distinctive cultural traits, Whitehead argues. Offspring who adopt their mothers' cultural traits survive and reproduce better than those who don't, leading to reduced genetic diversity, in his view.

There are other explanations for the genetic finding, however. For example, extensive human hunting of some killer whale populations may largely account for the animals' low genetic diversity, according to Mann.

"Still, social learning clearly seems to be important in many cetacean species," Mann says.

Chimp researcher Frans B.M. de Waal of Emory University in Atlanta agrees. De Waal listened with great interest to presentations by cetacean researchers at the recent Chicago symposium.

"It was a real eye-opener to see what cetaceans are capable of," he remarks. "Some scientists might argue about whether the word culture applies here, but cetaceans are clearly investing their intellectual energy in social knowledge and its transmission."


Herman, L.M., and R.K. Ukeyama. 1999. The dolphin's grammatical competency: Comments on Kako (1999). Animal Learning and Behavior 27(February):18.

Janik, V.M. 2000. Whistle matching in wild bottlenose dolphins (Tursiops truncatus). Science 289(Aug. 25):1355-1357. Available at http://www.sciencemag.org/cgi/content/full/289/5483/1355.

Rendell, L., and A. Whitehead. 2001. Culture in whales and dolphins. Behavioral and Brain Sciences 24(April):309-324. Abstract . Preprint available at http://www.bbsonline.org/documents/

Tyack, P.L. 2000. Dolphins whistle a signature tune. Science 289(Aug. 25):1310-1311. Summary available at http://www.sciencemag.org/cgi/content/summary/289/5483/1310.

Further Readings:

Bower, B. 1999. Chimps employ culture to branch out. Science News 155(June 19):388. References and sources available at http://www.sciencenews.org/pages/sn_arc99/6_19_99/fob1ref.htm.

Connor, R.C., J. Mann, et al. 1998. Social evolution in toothed whales. Trends in Ecology and Evolution 13(June 1):228-232. Abstract available at http://dx.doi.org/10.1016/S0169-5347(98)01326-3.


Louis M. Herman
Kewalo Basin Marine Mammal Laboratory
1129 Ala Moana Boulevard
Honolulu, HI 96814

Vincent M. Janik
Biology Department
Woods Hole Oceanographic Institution
Woods Hole, MA 02543

Luke Rendell
Department of Biology
Dalhousie University
Halifax, Nova Scotia B3H 4J1

Peter L. Tyack
Biology Department
Woods Hole Oceanographic Institution
Woods Hole, MA 02543



From Science News, Vol. 158, No. 18, Oct. 28, 2000, p. 284.

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