Science: Update

IN A study that breaks new ground in the understanding of sexual promiscuity, a team of scientists believe they may have found the answer to a question that has baffled birdwatchers for more than a century - how the weaver bird got its false penis.

Male buffalo weavers stimulate females to orgasm via a "phalloid organ" - which is not a true penis because it lacks any ducts or tubes for emitting semen - in order to encourage them to retain their sperm, according to a theory proposed in this week's Nature. So extraordinary is the stiff protuberance that people in the bird's native Namibia once thought the organ had nothing to do with sex at all, but was a handy device for carrying sticks to the nest.

Dr Tim Birkhead and colleagues from the University of Sheffield, however, have shown that the false penis is used to stimulate females during copulation for up to 30 minutes, which ends with a pronounced orgasm, the first time the phenomenon has been recorded in animals other than mammals.

"We found that the phalloid organ was not inserted into the female but rubbed against her lower abdomen as a form of stimulation," Dr Birkhead said. The scientists believe that the unusual mating arrangement of the weaver bird - two males copulating with the same female - causes intense competition which has resulted in the evolution of protracted copulation and the false penis. "Protracted copulation may be some kind of test of the male by females," Dr Birkhead said.

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EARTH MAY be sitting on the edge of an undiscovered field of asteroids that is quite separate from the most famous asteroid belt, between the orbits of Mars and Jupiter, which was discovered 200 years ago. Asteroid belts contain large lumps of rock and iron, often many miles across, thought to be left over from the formation of the solar system. Astronomers have also discovered objects in the Kuiper belt, a region of stable orbits in the solar system beyond Neptune.

Now it is thought that asteroids can congregate anywhere where they are undisturbed by the gravitational forces of planets that may disperse them. One such stable haven exists very close to the orbit of the Earth, scientists report in Nature. Serge Tabachnik from Oxford University calculated that the stable region lay between the Earth and Mars, but was closer to the Earth.

The scientists suggest that a population of hidden asteroids may lurk in this zone.

No hard evidence has been found to support the theory. But a search through the catalogues of near-Earth objects reveals several recently discovered bodies that could occupy such a belt.

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JAPANESE SCIENTISTS are using satellites to monitor the vertical motion of a buoy moored in the ocean to predict deadly tidal waves, New Scientist magazine reports.

The tidal waves, or tsunamis, are caused by underwater earthquakes, landslips or volcanic activity. When they hit land they are capable of destroying anything or anyone in their path.

"The idea of using a buoy may seem obvious, but it has only been made possible because of recent advances in GPS [Global Positioning System] technology," Teruyuki Kato, of Tokyo University's Earthquake Research Institute, told the magazine. The GPS network is made up of 24 satellites. They transmit time signals and receivers calculate their position so that vertical movement of the buoy can be calculated with an accuracy of a few centimetres.

Scientists can distinguish between possible tsunamis and normal waves because tidal waves have much longer wavelengths.