The real animal magic is how they talk to each other

Festival of science: Scientists plug into nature's quietest sounds. Charles Arthur reports
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The Independent Online
If Dr Dolittle really did talk to the animals, then he must have had the most remarkable vocal cords, not to mention ears, wings and (if he spoke at all to fish) a swim bladder.

The reason, the British Association heard yesterday, is that scientists have discovered that species as diverse as elephants, bats, bees and haddock all use entirely different systems to communicate across a superhuman range of frequencies. The topics, though, tend to focus on two eternal topics: sex and food.

Elephants use their vocal cords to generate infrasonic noises, ranging from 15 to 35 Hertz (Hz), according to Dr Bill Langbauer of Pittsburgh Zoo in the United States. "They can communicate over more than two miles," he said. "But the majority of it is inaudible to humans." The normal human hearing range is from 20Hz to 20,000Hz.

The newly recognised noises "explain a lot of behaviour that was a mystery before, such as how elephants co-ordinate their behaviour across long distances."

A principal use is by the female elephant, which only becomes receptive to sex for about four days in every four years. "They use infrasonic calls lasting four to five seconds, repeated for up to 45 minutes," Dr Langbauer said.

"It's really well-designed for letting other elephants know where she is, because the higher-pitched harmonics are attenuated with distance. The more harmonics the male elephant hears, the nearer he knows she is."

However, bees go a step further. German scientists have now determined that when a bee "dances" inside the hive to describe the direction and distance to food, the bees nearby actually "hear" the air currents it generates - and those are as loud to them as standing near a jet plane taking off would be to us.

"We have known about the dance of the bee since 1946," said Professor Axel Michelson of Odense University. "But what was not explained was how they could see this, since the beehive is often absolutely dark."

Scientists suspected that the air pressure created by the movements of the dancing bee's wings, allied to the waggling of its body - all of which encode the journey to food - might trigger the surrounding bees' antennae. By sensing the changes in air currents, the bees could work out what movements were being made, even in the dark.

To test this, the researchers built a robot bee from brass, with a single wing made of a piece of razor blade. By waggling the wing and moving the body, they found that the bees were reacting to changes in air pressure caused by the wing flapping up and down.

"The air moves at about 1m per second over the wings, which for us would be like getting close to a jet engine," he said. "But the pressure falls off very quickly with distance. A metre away, the surrounding bees cannot feel anything. When you live somewhere with 50,000 others, it's valuable to have a way of telling something that's not audible to everybody."

Bats turn out to have two systems for detecting food and objects - depending on whether they feed on moving items, such as insects and small animals, or static ones, such as fruit or (in the case of the vampire bat) blood from sleeping animals.

Professor David Pye, of the University of London, found that bats which detect moving objects use a singe frequency sound, because when that is reflected back it will be shifted upwards or downwards, rather like the whistle of a moving train. By contrast, bats which rely on static prey put out a sweep of frequencies, which is better for measuring distance.

However, possibly the strangest noises of all belong to the common haddock. Professor Tony Hawkins, director of the Scottish Marine Laboratory, explained that male haddock make a knocking sound by contracting the muscles in their swim bladder, the fluid-filled sac that lets them control their buoyancy. The pressure wave is transmitted outwards to other fish.

The knocking sound normally indicates aggression, and is repeated about once a second. But when a female approaches the noise becomes more rapid, soon reaching many beats per second - requiring muscle twitches faster than any other vertebrate animal.

"The male sticks its fins up, and becomes worked up, and then the two fish embrace - they really wrap their fins around each other - and the noise from the male gets louder. Then the female releases millions of eggs and the male releases its sperm, which are fertilised in the water around them."

It is, he adds, "one of the more interesting animals." Dr Dolittle would surely agree - if his Victorian outlook would allow, of course.

(To preserve the dignity of the humble haddock, The Independent is not carrying a photograph of its more intimate moments.)

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