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Dolphins, like humans, recognize names

Tuesday, May 9, 2006; Posted: 10:34 a.m. EDT (14:34 GMT)

A new study indicates dolphins recognize names even when voice cues are removed from the sound.

WASHINGTON (Reuters) -- Bottlenose dolphins can call each other by name when they whistle, making them the only animals besides humans known to recognize such identity information, scientists reported on Monday.

Scientists have long known that dolphins' whistling calls include repeated information thought to be their names, but a new study indicates dolphins recognize these names even when voice cues are removed from the sound.

For example, a dolphin might be expected to recognize its name if called by its mother, but the new study found most dolphins recognized names -- their signature whistles -- even when emitted without inflection or other vocal cues.

More than that, two dolphins may refer to a third by the third animal's name, said Laela Sayigh, one of three authors of a paper published in the Proceedings of the National Academy of Sciences.

"They are known to produce these individually distinctive signature whistles, like names," Sayigh said in a telephone interview. She said the researchers wanted to know what information in the whistles helped dolphins identify each other's names.

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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).

Turning to 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).

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Dolphins are widely believed to be amongst the most intelligent of all animals. It is sometimes said that dolphins are roughly as intelligent as a two-year-old human. [citation needed] However, experts in comparative psychology or animal cognition would be reluctant to make any such estimate, as quantitative comparisons of intelligence between species are notoriously difficult to make in principle.[citation needed] Straightforward comparisons of species' relative intelligence are complicated by differences in sensory apparatus, response modes, and nature of cognition; furthermore, the difficulty and expense of doing experimental work with a large marine animal mean that even such tests as can meaningfully be done have still not been done, or have been carried out with inadequate sample size and methodology. See the Dolphin intelligence article for more details.

Dolphins often leap above the water surface, sometimes performing acrobatic figures (e.g. the spinner dolphin). Scientists aren't quite certain about the purpose of this behavior, but it may be to locate schools of fish by looking at above water signs, like feeding birds. They could also be communicating to other dolphins to join a hunt, attempting to dislodge parasites, or simply doing it for fun. Play is a very important part of dolphins' lives and they can often be observed playing with seaweed or playfighting with other dolphins. They have even been seen harassing other creatures, like seabirds and turtles. Dolphins also seem to enjoy riding waves and are frequently seen 'surfing' coastal swells and the bow waves of boats.

They are also famous for their willingness to occasionally approach humans and playfully interact with them in the water. In return, in some cultures like in Ancient Greece they were treated with welcome; a ship spotting dolphins riding in their wake was considered a good omen for a smooth voyage. There are many stories of dolphins protecting shipwrecked sailors against sharks by swimming circles around the swimmers. A school of dolphins is also said to have pushed a fishing boat which was returning, back out to sea after sensing the underwater disturbances generated by the 2004 Asian Tsunami

Dolphins are social animals, living in pods (also called "schools") of up to a dozen animals. In places with a high abundance of food, schools can join temporarily, forming an aggregation called a superpod; such groupings may exceed 1000 dolphins. The individuals communicate using a variety of clicks, whistles and other vocalizations. They also use ultrasonic sounds for echolocation.

Membership in schools is not rigid; interchange is common. However, the animals can establish strong bonds between each other. This leads to them staying with injured or ill fellows for support.

Because of their high capacity for learning, dolphins have been employed by humans for any number of purposes. Dolphins trained to perform in front of an audience have become a favorite attraction in dolphinaria, for example SeaWorld. Dolphin/Human interaction is also employed in a curative sense at places where dolphins work with autistic or otherwise disabled children. The military has employed dolphins for various purposes from finding mines to rescuing lost or trapped persons. Such military dolphins, however, drew scrutiny during the Vietnam War when rumors circulated that dolphins were being trained to kill Vietnamese Skin Divers.

Reports of cooperative human-dolphin fisheries date back to Pliny. A modern human-dolphin fishery was reported in Laguna, Santa Catarina, Brazil in 1990. The transmission of this behavior appears to be matrilineal.

In May 2005, researchers in Australia discovered a cultural aspect of dolphin behaviour: Some dolphins (Tursiops aduncus) teach their offspring to use tools. The animals break off sponges and put them onto their mouths thus protecting the delicate body part during their hunt for fish on the seabed. Unlike the sharing among all of the group by simian primates, dolphins mostly hand their knowledge of how to use a tool from mothers to daughters. The technology to use sponges as mouth protection is not genetically inherited but a taught cultural behaviour.

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