Dolphins sing 'Batman' theme
Source: Jennifer Viegas, Discovery News
Monday, 3 October 2005
Dolphins are the only mammals other than humans to recognise rhythms and reproduce them vocally.
Scientists have taught dolphins to combine both rhythm and vocalisations to produce music, resulting in an extremely high-pitched, short version of the Batman theme song.
The findings, outlined in two studies, are the first time that nonhuman mammals have demonstrated they can recognise rhythms and reproduce them vocally.
"Humans are sensitive to rhythms embedded in sequences of sounds, but we typically consider this skill to be part of processing for language and music, cognitive domains that we consider to be uniquely human," says Professor Heidi Harley, lead author of both studies.
"Clearly, aspects of those domains are available to other species."
The studies will be presented at the joint meeting of the Acoustical Society of America and NOISE-CON 2005, which runs from 17 to 21 October in Minneapolis.
Learning to sing
Harley, who is associate professor of social sciences at the New College of Florida in Sarasota, says that both studies tested dolphins at Disney's Epcot Center in Florida.
The researchers first had an adult male bottlenose dolphin position itself in front of an underwater sound projector, called a hydrophone, that produced six different 14 kiloherz, 4 second rhythms.
The dolphin was rewarded for performing a certain behaviour to each rhythm. For example, when rhythm 1 played, it waved its pectoral fin and when rhythm 2 played, it tossed a ball.
The various rhythms were played at different frequencies and tempos to ensure the dolphin was recognising rhythms instead of just frequencies or sound durations.
Another adult male was trained to produce similar rhythms using a pneumatic switch, essentially a small, air-filled ball connected to a computer that then generated sounds whenever the dolphin pressed the switch.
"The dolphin was reinforced for producing a specific rhythm to a specific object," says Harley.
"For example, when we presented him with a Batman doll, he received a fish for producing a specific rhythm, in this case, a short sound and then a long one."
"If you recall the original Batman TV series musical intro you'll probably remember the way they sang 'Bat-maaaaaaaan'," she adds.
The dolphin spontaneously vocalised to the rhythms, so the researchers started to reward the male with fish whenever it matched its 'singing' to the rhythms.
By the end of the studies, the scientists could show an object, such as the Batman doll, which represented a certain rhythm-vocalisation combo to the dolphin, and it would create the correct sounds both vocally and using the switch.
Gordon Bauer, associate professor of psychology at the New College of Florida who did not work on the studies, says, "This is the first report, to my knowledge, of a nonhuman mammal's ability to discriminate rhythmic patterns."
But Bauer doubts that dolphins realise they are producing what people consider 'music'.
"I think music is a human construct," he says. "I doubt that it has pertinence to animals, although the elements of music, such as pitch, time, timbre, rhythm, etc, may be incorporated into animal communication."
Harley agrees, and hopes the everyday vocalisations of dolphins will be analysed in terms of their rhythmic content.
In the near future, she and her team are planning to test the dolphins on their ability to recognise recordings of their own rhythms by having them associate their own sound creations with identifying objects similar to the Batman doll.
All about dolphins and sound
Ancient Greek mariners listened to the sounds of dolphins through the hulls of their ships.
People have been fascinated by dolphin sounds for millennia. Yet, we still don't know what 'they' are talking about!
Dolphin sounds fall into several main categories:
Whistles: which are unique to each individual animal - much like our own voices. It appears that dolphins use these 'signature whistles' like we use names. You often hear a loud whistle from a nearby dolphin, followed by a similar sounding whistle from another dolphin. Sort of like a sound 'handshake' or greeting.
Clicks: which are generally used for some form of echolocation. Echolocation works like 'radar' and is used by dolphins to find food - like schooling fish. The dolphin makes a 'click' which travels through the water, bounces off an object like a fish, and then hears the echo.
Chirps: which are tones of varying frequency - their purpose is not known.
These dolphin sounds are well within the hearing range of people. While echo location clicks can range up to about 150,000 Hz (about 8 times higher than the normal human hearing range), a lot of these clicks occur at frequencies as low as about 2,000 Hz. So people can easily hear them with the proper hydrophone (underwater microphone).
It is reported that cetaceans have a large portion of their brains devoted to auditory senses. Therefore they may be able to convert sound into an acoustic image in a section of their brains which allows them to 'see' in the darkness of the ocean, or in the murky waters of river deltas. There are many 'noise' sources in the ocean that could act to 'illuminate' objects with sound that cetaceans detect. For example, in shallow tropical and semi-tropical waters, snapping shrimp product continuous 'clicking' noises. These may allow cetaceans to 'see' fish without the need to use their own echo location - which might alert fish of their presence. Further out in the ocean, ambient sounds from wave action may serve the same purpose.
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