Cetacean intelligence


Cetacean intelligence is the overall intelligence and derived cognitive ability of aquatic mammals belonging in the infraorder Cetacea, including baleen whales, porpoises, and dolphins. In 2014, a study found that the long-finned pilot whale has more neocortical neurons than any other mammal, including humans, examined to date.

Brain

Size

was previously considered a major indicator of the intelligence of an animal. However, many other factors also affect intelligence, and recent discoveries concerning bird intelligence have called the influence of brain size into question. Since most of the brain is used for maintaining bodily functions, greater ratios of brain to body mass may increase the amount of brain mass available for more complex cognitive tasks. Allometric analysis indicates that in general, mammalian brain size scales at approximately the or exponent of body mass. Comparison of actual brain size with the size expected from allometry provides an encephalization quotient that can be used as a more accurate indicator of an animal's intelligence.
Spindle cells have been discovered in the brains of the humpback whale, fin whale, sperm whale, orca, bottlenose dolphins, Risso's dolphins, and beluga whales. Although spindle cells initially attracted significant interest because it was believed that they were restricted to other highly encephalized or socially complex species such as humans, great apes, and elephants, this was revised by later research which discovered spindle cells in a wider range of mammalian species and taxa, including domestic sheep, cows, the pygmy hippopotamus, and white-tailed deer, suggesting a more basal function. Other researchers have questioned whether the spindle cells discovered in non-hominid species such as dolphins correspond to the specialized-stick-corkscrew-cells described by von Economo as distinct from the more commonly found spindle cells.

Structure

brains also show a complexity similar to dolphin brains, and are also more convoluted than that of humans, and with a cortex thicker than that of cetaceans. It is generally agreed that the growth of the neocortex, both absolutely and relative to the rest of the brain, during human evolution, has been responsible for the evolution of human intelligence, however defined. While a complex neocortex usually indicates high intelligence, there are exceptions. For example, the echidna has a highly developed brain, yet is not widely considered very intelligent, though preliminary investigations into their intelligence suggest that echidnas are capable of more advanced cognitive tasks than were previously assumed.
In 2014, it was shown for the first time that a species of dolphin, the long-finned pilot whale, has more neocortical neurons than any mammal studied to date including humans.
Unlike terrestrial mammals, dolphin brains contain a paralimbic lobe, which may possibly be used for sensory processing. It has also been suggested that similar to humans, the paralimbic region of the brain is responsible for a dolphin's self-control, motivation, and emotions. The dolphin is a voluntary breather, even during sleep, with the result that veterinary anaesthesia of dolphins 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. 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.
The dolphin's greater dependence on 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 as large. Sensory experiments suggest a great degree of cross-modal integration in the processing of shapes between echolocative and visual areas of the brain.

Brain evolution

The evolution of encephalization in cetaceans is similar to that in primates. Though the general trend in their evolutionary history increased brain mass, body mass, and encephalization quotient, a few lineages actually underwent decephalization, although the selective pressures that caused this are still under debate. Among cetaceans, Odontoceti tend to have higher encephalization quotients than Mysticeti, which is at least partially due to the fact that Mysticeti have much larger body masses without a compensating increase in brain mass. As far as which selective pressures drove the encephalization of cetacean brains, current research espouses a few main theories. The most promising suggests that cetacean brain size and complexity increased to support complex social relations. It could also have been driven by changes in diet, the emergence of echolocation, or an increase in territorial range.

Problem-solving ability

Some research shows that dolphins, among other animals, understand concepts such as numerical continuity, though not necessarily counting. Dolphins may be able to discriminate between numbers.
Several researchers observing animals' ability to learn set formation tend to rank dolphins at about the level of elephants in intelligence, and show that dolphins do not surpass other highly intelligent animals in problem solving. A 1982 survey of other studies showed that in the learning of "set formation", dolphins rank highly, but not as high as some other animals.

Behavior

Pod characteristics

Dolphin group sizes vary quite dramatically. River dolphins usually congregate in fairly small groups from 6 to 12 in number or, in some species, singly or in pairs. The individuals in these small groups know and recognize one another. Other species such as the oceanic pantropical spotted dolphin, common dolphin and spinner dolphin travel in large groups of hundreds of individuals. It is unknown whether every member of the group is acquainted with every other. However, large packs can act as a single cohesive unitobservations 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 near neighbors but also of other individuals nearby in a similar manner to which humans perform "audience waves". This is achieved by sight and possibly echolocation. One hypothesis proposed by Jerison is that members of a pod of dolphins are able to share echolocation results with each other to create a better understanding of their surroundings.
Southern resident orcas in British Columbia, Canada, and Washington, United States, live in extended family groups. The basis of the southern resident orca social structure is the matriline, consisting of a matriarch and her descendants of all generations. A number of matrilines form a southern resident orca pod, which is ongoing and extremely stable in membership, and has its own dialect which is stable over time. A southern resident calf is born into the pod of their mother and remains in it for life.
A cetacean dialect is a socially–determined vocal tradition. The complex vocal communication systems of orcas correspond with their large brains and complex social structure. The three southern resident orca pods share some calls with one another, and also have unique calls. Discussing the function of resident orca dialects, researchers John Ford, Graeme Ellis and Ken Balcomb wrote, "It may well be that dialects are used by the whales as acoustic indicators of group identity and membership, which might serve to preserve the integrity and cohesiveness of the social unit." Resident orcas form closed societies with no emigration or dispersal of individuals, and no gene flow with other orca populations. There is evidence that other species of dolphins may also have dialects.
In bottlenose dolphin studies by Wells in Sarasota, Florida, and Smolker in Shark Bay, Australia, females of 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.
The complex social strategies of marine mammals such as bottlenose dolphins, "provide interesting parallels" with the social strategies of elephants and chimpanzees.