Cetacean intelligence

Cetacean intelligence denotes the cognitive capabilities of the cetacean order of mammals and especially the various species of dolphin. Cetaceans include whales, porpoises, and dolphins, and while all are broadly considered intelligent, dolphins have generated the most attention as their capabilities appear to be of a different order than that of their relatives.

Conclusions about the nature and magnitude of dolphin intelligence have not yet been reached. There are many different species of dolphin (see the cetacea article for a full list) and generalisations can be easily misapplied; cognitive differences between dolphin species may be as marked as differences between humans and the great apes.

Brain characteristics

While there is no physiological characteristic that unequivocally indicates intelligence in animals, scientists naturally focus on brain size and structure. Absolute brain size does appear to correlate to intelligence,[1] but it is a crude measure, given that animal species vary in size over many orders of magnitude. Brain-to-body ratio is considered a more precise benchmark, particularly for species that are otherwise similar in size (the larger the species, the smaller the brain-to-body mass ratios as a general rule). Comparing a land-based species and water-based species introduces a further complication because their habitats make hugely differing demands. Even accepting these caveats, dolphin brain characteristics appear positive indicators of advanced intelligence.

Bottle-nosed dolphins (Tursiops truncatus) have an absolute brain mass of 1500-1700 grams. This is slightly greater than that of humans (1300-1400 grams) and about four times that of chimpanzees (400 grams) [2].
The brain-to-body ratio in dolphins is less than half that of humans: 0.9% versus 2.1%.[3] This comparison appears more favourable if we leave aside the large amount of blubber (15-20% of mass) dolphins require for insulation. Humans and dolphins rate first and second, respectively, for animal brain-to-body ratio, among all animals weighing over one kilogram.
At birth, dolphins have a brain mass that is 42.5% of an adult dolphin's brain mass (in comparison with 25% for human newborns). By eighteen months, the brain mass of Bottle-nosed dolphins is roughly 80% of that of an adult dolphin. Human beings generally do not achieve this figure until the age of three or four (ibid).

Regarding brain structure and the complexity of neural connections, dolphins continue to compare favourably to humans.

A cerebral cortex 40% larger than human beings, with "wrinkles" of near equivalent complexity [4].
A similarly developed frontal lobe (ibid).

Differences from other mammalian brains

Although dolphins are themselves mammals, their brains are constructed and act differently from those of most mammals. Unlike most mammalian brains, which have six neocortical layers, dolphins have five. While most sleeping mammals go through a stage known as REM sleep, dolphin studies have not shown any brain wave patterns associated with REM sleep. Unlike terrestrial mammals, dolphin brains contain a paralimbic lobe, which may possibly be used for sensory processing. The dolphin is a voluntary breather, even in sleep, with the result that veterinary anesthesia of dolphins is impossible, as it would result in asphyxiation. Ridgway reports that EEGs show alternating hemispheric asymmetry in slow waves during sleep, with occasional sleep-like waves from both hemispheres.^{[citation needed]} This result has been interpreted to mean that dolphins sleep only one hemisphere of their brain at a time, possibly to control their voluntary respiration system or to be vigilant for predators.

Dolphin brain stem transmission time is faster than that normally found in humans, and is roughly equivalent to the speed found in rats. As echo-location is the dolphin's primary means of sensing its environment -- analogous to eyes in primates -- and since sound travels four and a half times faster in water than in air, scientists speculate that the faster brain stem transmission time, and perhaps the paralimbic lobe as well, support speedy processing of sound. The dolphin's dependence on speedy sound processing is evident in the structure of its brain: its neural area devoted to visual imaging is only about one-tenth that of the human brain, while the area devoted to acoustical imaging is about 10 times that of the human brain. (This is unsurprising: primate brains devote far more volume to visual processing than almost any other animals, and human brains more than other primates.) Sensory experiments suggest a high degree of cross-modal integration in the processing of shapes between echolocative and visual areas of the brain. Unlike the case of the human brain, the cetacean optic chiasm is completely crossed, and there is behavioral evidence for hemispheric dominance for vision.

The neocortex of the cetacean brain has a highly developed layer I and VI, which is a pattern that has been labeled "archaic" or phylogenetically primitive and superficially similar to that of hedgehogs.^{[citation needed]} Therefore the evolutionary development of the cetacean brain has taken a different route than that of advanced terrestrial ones.

Behavior

See also animal behavior for a broader view.

Researching the behavior of dolphins in the wild is a difficult task. However, several researchers have examined the social behavior of dolphins and tried to extract an understanding of the level of communication between individuals, which in turn is interpreted as a measure of intelligence.

Pack characteristics

Dolphin group sizes vary quite dramatically. River dolphins usually congregate in fairly small groups, from 6 to 12 in number. Researchers believe that the individuals in these small groups may well know and recognise one another.^{[citation needed]} Other species such as the oceanic Pantropical Spotted Dolphin, Heaviside's Dolphin and Spinner Dolphin travel in large groups of hundreds of individuals. It is extremely unlikely that every member of the group is acquainted with every other. However, there is no doubt that such large packs can act as a single cohesive unit - observations show that if an unexpected disturbance, such as a shark approach, occurs from the flank or from beneath the group, the group moves in near-unison to avoid the threat. This means that the dolphins must be aware not only of their next-door neighbours but also of other individuals nearby - in a similar manner to which humans perform "Audience waves". This is achieved by sight, and possibly also echolocation. One speculative hypothesis proposed by Jerison (1986) is that the pack of dolphins are able to share echolocation results between each other to create a better understanding of their surroundings.^{[citation needed]}

Resident orcas living in British Columbia, Canada, and Washington, USA live in extremely stable family groups. The basis of this social structure is the matriline, consisting of a mother and her offspring, who travel with her for life. Male orcas never leave their mother's pod, while female offspring may branch off to form their own matriline if they have many offspring of their own. Males have a particularly strong bond with their mother, and travel with them their entire lives, which can exceed 50 years. It is an interesting notion, as they do not benefit from this except perhaps in hunting techniques, although they could join other groups to hunt. There are two interesting examples of this familial bond in males. Two male sons, known scientifically as A38 and A39, constantly accompany their mother A30, despite that she needs no protection and they can all hunt by themselves, and rarely leave her side. Researchers have noted that if one son does wander off, one always remains with the mother. Another example are the brothers A32, A37 and A46, whose mother (A36) died. Instead of the family disbanding, the three brothers remain constantly together.

Relationships in the orca population can be discovered through their vocalizations. Matrilines who share a common ancestor from only a few generations back share mostly the same dialect, making up a pod. Pods who share some calls indicate a common ancestor from many generations back, and make up a clan. Interestingly, the orcas use these dialects to avoid in-breeding. They mate outside the clan, which is determined by the different vocalizations. On one occasion, an orca's mother and father were determined to be in the same clan, although in different pods.

In bottlenose dolphin studies by Wells in Sarasota, Florida, and Smolker in Shark Bay, Australia, females in a community are all linked either directly or through a mutual association in an overall social structure known as fission-fusion. Groups of the strongest association are known as "bands," and their composition can remain stable over years. There is some genetic evidence that band members may be related, but these bands are not necessarily limited to a single matrilineal line. There is no evidence that bands compete with each other. In the same research areas, as well as in Moray Firth, Scotland, males form strong associations of two to three individuals, with a coefficient of association between 70 and 100. These groups of males are known as "alliances," and members often display synchronous behaviors such as respiration, jumping, and breaching. Alliance composition is stable on the order of tens of years, and may provide a benefit for the acquisition of females for mating. There is evidence that males in alliances are not related, and that males tend to disperse from their natal area. Connor reports that alliances may form temporary alliances known as "super-alliances" or second-order alliances, primarily for the purpose of acquiring females from other alliances or super-alliances. Current research is attempting to determine if these examples of cooperation are remembered for the purpose of reciprocation, because the recruited first-order alliances do not seem to acquire the female for themselves. It is notable that second-order alliances in bottlenose dolphins are one of the most hierarchically complex social structures observed in the animal kingdom, excluding the human species. ^{[citation needed]}

Complex play

Dolphins are known to engage in complex play behavior, which includes such things as producing stable underwater toroidal air-core vortex rings or "bubble rings"[5]. There are two main methods of bubble ring production: rapid puffing of a burst of air into the water and allowing it to rise to the surface, forming a ring; or swimming repeatedly in a circle and then stopping to inject air into the helical vortex currents thus formed. The dolphin will often then examine its creation visually and with sonar. They also appear to enjoy biting the vortex-rings they've created, so that they burst into many separate normal bubbles and then rise quickly to the surface. [6] Certain whales are also known to produce bubble rings, or even bubble-nets for the purpose of foraging. Many dolphin species are also known for playing by riding in waves, whether natural waves near the shoreline in a method akin to human "body-surfing", or within the waves induced by the bow of a moving boat in a behavior known as bow-riding.

Creative behavior

Not only have dolphins exhibited the ability to learn complex tricks, they have also demonstrated the ability to produce creative responses. This was studied by Karen Pryor in the mid-sixties at Sea Life Park in Hawaii, and was published as "The Creative Porpoise: Training for Novel Behavior" in 1969. The two test subjects were two rough-toothed dolphins (Steno bredanensis), called Malia (a regular show performer at Sea Life Park) and Hou (a research subject at adjacent Oceanic Institute). The experiment tested when and whether the dolphins would identify that they were being rewarded (by fish) for originality in behaviour. So the trainer would reward the dolphin for a novel behaviour, but would not if the same behaviour was repeated. The experiment was highly successful. Malia finally learned what was expected after a few days, and from the fifteenth session produced an original behaviour to get a reward. Hou took thirty-three sessions to reach the same stage. On each occasion the experiment was stopped when the variability of dolphin behaviour became too complex to make further positive reinforcing meaningful.

The same experiment was repeated with humans, and it took the volunteers about the same length of time to figure out what was being asked of them. After an initial period of frustration or anger, the humans realised they were being rewarded for novel behaviour. In dolphins this realisation produced excitement and more and more novel behaviours - in humans it mostly just produced relief. [7]

Captive orcas have often displayed interesting responses when they get 'bored' with activities. For instance, when Dr Paul Spong worked with the orca Skana, he researched her visual skills. However, after performing favourably in the 72 trials per day, Skana suddenly began consistently getting every answer wrong. Dr Spong concluded that a few fish were not enough motivation. He began playing music, which seemed to provide Skana with much more motivation.

Use of tools

As of 2005, scientists have observed limited groups of bottle nose dolphins around the Australian Pacific using a basic tool. When scavenging for food on the sea floor, many of these dolphins were seen tearing off pieces of sponge and wrapping them around their "bottle nose" to prevent abrasions; illustrating yet another complex cognitive process thought to be limited to the great apes.[8]

Communication

Dolphins emit two very distinct kinds of acoustic signals, which we call whistles and clicks.

Clicks - quick broadband burst pulses - are used for echolocation, although some lower-frequency broadband vocalizations may serve a non-echolocative purpose such as communication; for example, the pulsed calls of Orcas. Pulses in a click train at intervals of ~35-50 milliseconds, and in general these inter-click intervals are slightly greater than the round-trip time of sound to the target.
Whistles - narrow-band frequency modulated (FM) signals - are used for communicative purposes, such as contact calls, the pod-specific dialects of resident Orcas, or the signature whistle of bottlenose dolphins.

There is strong evidence that some specific whistles, called signature whistles, are used by dolphins to identify and/or call each other; dolphins have been observed emitting both other specimens' signature whistles, and their own. A unique signature whistle develops quite early in a dolphin's life, and it appears to be created in an imitation of the signature whistle of the dolphin's mother. [9]

Xitco reported the ability of dolphins to passively eavesdrop on the active echolocative inspection of an object by another dolphin. Herman calls this effect the "acoustic flashlight" hypothesis, and may be related to findings by both Herman and Xitco on the comprehension of variations on the pointing gesture, including human pointing, dolphin postural pointing, and human gaze, in the sense of a redirection of another individual's attention, an ability which may require theory of mind.

The environment where dolphins live makes experiments much more expensive and complicated than for other species; additionally, the fact that cetaceans can emit and hear sounds (which are believed to be their main means of communication) in a range of frequencies much wider than humans' means that sophisticated equipment, which was scarcely available in the past, is needed to record and analyse them. For example, clicks can contain significant energy in frequencies greater than 110 KHz (for comparison, it is unusual for a human to be able to hear sounds above 20 kHz), requiring that equipment have a sampling rates of at least 220 kHz; MHz-capable hardware is often used.

In addition to the acoustic communication channel, the visual modality is also significant. The contrasting pigmentation of the body may be used, for example with "flashes" of the hypopigmented ventral area of some species, as can the production of bubble streams during signature whistling. Also, much of the synchronous and cooperative behaviors, as described in the Behavior section of this entry, as well as cooperative foraging methods, likely are managed at least in part through visual means.

Whilst there is little evidence for dolphin language, experiments have shown that they can learn human sign language. Akeakamai, a bottle nosed dolphin, was able to understand both individual words and basic sentences like "touch the frisbee with your tail and then jump over it" (Herman, Richards, & Wolz 1984).

Self-awareness

Self-awareness shows highly-developed, abstract thinking. Self-awareness is the precursor to more advanced processes like meta-cognitive reasoning (thinking about thinking) that are typical of humans. Scientific research into self-awareness has suggested that bottlenose dolphins possess self-awareness.^{[citation needed]} Dolphins differ markedly, so an assessment can not be made for all species, some of which have much smaller brain sizes and presumably different structures.

The standard test for self-awareness in animals is the mirror test, developed by Gordon Gallup in the 1970s, in which a temporary dye is placed on an animal's body, and the animal is then presented with a mirror. Most animals react to a mirror as if it is another animal. However, like great apes, dolphins have been shown to recognise the mirror image as themselves, by examining the marking on their body. Evidence for mirror recognition by dolphins was anecdotal until the 1990s, when the scientific studies carried out by researchers Marten and Psarakos (1994, 1995) and Reiss and Marino (1998) claims it has succeeded in the confirmation.

Some scientists still disagree with these findings, arguing that the results of these tests are open to human interpretation. This test is far less definitive than when used for primates, because primates can touch the mark or the mirror, while dolphins cannot, making their alleged self-recognition behaviour less clear. Critics argue that behaviours that are said to identify self-awareness resemble existing social behaviours, and so researchers could be mislabelling social responses to another dolphin. The researchers counter-argue that the behaviours shown to evidence self-awareness are very different to normal responses to another dolphin, including paying significantly more attention to another dolphin than towards their mirror image. Dr. Gallup called the results "the most suggestive evidence to date" of mirror self-recognition in dolphins, but "not definitive" because he was not entirely clear that the dolphins were not interpreting the image in the mirror as another animal.

As a further response to these criticisms, in 1995, Marten and Psarakos used television to test dolphin self-awareness. They showed dolphins real-time footage of themselves, recorded footage, and another dolphin. They concluded that their evidence suggested self-awareness rather than social behaviour. This study has not been repeated since then, however, so the results remain unverified.

Comparative Cognition

The area of the comparative cognition (see animal cognition) of the dolphin is one of the primary avenues of the investigation of cetacean intelligence.

Examples of cognitive abilities investigated in the dolphin include concept formation, sensory skills, and the use of mental representation of dolphins. Such research has been ongoing since the late 1970s, and include the specific areas of: acoustic mimicry, behavioral mimicry (inter- and intra-specific), comprehension of novel sequences in an artificial language (including non-finite state grammars as well as novel anomalous sequences), memory, monitoring of self-behaviors (including reporting on these, as well as avoiding or repeating them), reporting on the presence and absence of objects, object categorization, discrimination and matching (identity matching to sample, delayed matching to sample, arbitrary matching to sample, matching across echolocation and vision, reporting that no identity match exists, etc.), synchronous creative behaviors between two animals, comprehension of symbols for various body parts, comprehension of the pointing gesture and gaze (as made by dolphins or humans), problem solving, echolocative eavesdropping, and more. Some researchers include Louis Herman, Mark Xitco, John Gory, Stan Kuczaj, Adam Pack, and many others.

While these are largely laboratory studies, field studies relating to dolphin and cetacean cognition are also relevant to the issue of intelligence, including those proposing tool use, culture, fission-fusion social structure (including tracking alliances and other cooperative behavior), acoustic behavior (bottlenosed dolphin signature whistles, sperm whale clicks, orca pod vocalizations), foraging methods (partial beaching, cooperation with human fishermen, herding fish into a ball, etc.). See: John Connor, Hal Whitehead, Peter Tyack, Janet Mann, Randall Wells, Kenneth Norris, B. Wursig, John Ford, Louis Herman, Diana Reiss, Lori Marino, Sam Ridgway, Paul Nachtigall, Eduardo Mercado, Denise Herzing, Whitlow Au.

In contrast to the primates, cetaceans are particularly far-removed from humans in evolutionary time. Therefore, cognitive abilities generally cannot be claimed to derive from a common ancestor, whereas such claims are sometimes made by researchers studying primate cognition. Any common ancestors of cetaceans and humans were almost certainly of distinctly inferior cognitive abilities than their modern descendants.

References and external links

Cetacean Brain

Brain facts and figures.
The dolphin brain a scholarly page at the University of Colorado, Boulder.
The Dolphin Brain Atlas A collection of stained brain sections and MRI images.
Bottle-nose dolphin brain from the comparative mammalian brain collection.
Dolphin brains, an AAAS Science Netlinks feature.
Brains, Behaviour and Intelligence in Cetaceans (Whales, Dolphins and Porpoises) A review of scientific literature in the field which was originally written for a conference on "ethical whaling practices" and later published in the British tabloid "New Scientist". (Caveat: This article purports to be a fair look at dolphin intelligence, yet entirely omits any mention of the decades of published findings by Dr. Louis M. Herman and others at the Univ. of Hawaii Kewalo Basin Marine Mammal Lab).

Popular Media

Deep thinkers Article from the Guardian about dolphin intelligence
Google group post on theories of dolphin brain size by "draygon@aol.com", a junior level biology (zoology) student at the University of Texas at El Paso Will be useful for article
Prologue to encounters with Whales and Dolphins Interesting article mainly on research difficulties with whales and dolphins
Dolphins as dimwits Recent research suggests dolphins are actually less intelligent than many species

Scientific or Academic Sources

BAYWATCH.(bottlenose dolphins research) Article on research into dolphins at Sarasota Bay
Memory for recent actions in the bottlenose dolphin (Tursiops truncatus): Repetition of arbitrary behaviors using an abstract rule Research study examining ability of dolphins to remember, learn and abstract.
Modern Reinforcement-Related Learning Theories Summary of research
The Dolphin Insitute Affiliated with Louis Herman's Kewalo Basin Marine Mammal Laboratory. See also their dolphin publications list for cognitive and sensory research.
Science News Article about usage of tools.

Self awareness research

Evidence of self-awareness in the bottlenose dolphin Academic study on dolphin self awareness by Marten and Psarakos(1994)
Using Self-View Television to Distinguish between Self-Examination and Social Behavior in the Bottlenose Dolphin (Tursiops truncatus) Another study by Marten and Psarakos on self reflection using TV (1995)
Mirror self-recognition in the bottlenose dolphin: A case of cognitive convergence Academic study on self awareness by Reiss and Marino (1998)
Hey, That's Me! Measuring a Dolphin's Intelligence with a Mirror Popularized article on Reiss and Marino study on self awareness.
Dolphin Self-Recognition Mirrors Our Own Another article on Reiss and Marino study
Research suggests dolphins capable of self-recognition Article on two studies on self recognition in dolphins

Other or Uncategorized

Towards Communication with Dolphins Project using computer software to try to understand dolphin communication
Open source software for researching dolphin communication using emission and recognition of underwater whistles
Vladimir I. Markov and Vera M. Ostrovskaya: [http://www.dauphinlibre.be/markovhtm.pdf