Bats have 'internal compass'

Last Modified: 27 Feb 2008
Source: PA News

Animal magnetism helps bats to navigate over long distances, scientists have learned.

The animals have a magnetic mineral in their bodies which acts as an internal compass, a study has shown.

Researchers were able to confuse a group of bats by subjecting them to a powerful magnetic pulse, but orientated the opposite way to the Earth's own field. They believe the pulse affected magnetite in the bats' cells. The study findings are published in the latest issue of the journal PLoS One.

The iron oxide mineral is found in a wide range of fish, birds and mammals, including humans. It has been suggested as a navigation aid in homing pigeons and aquatic species such as whales, sharks and tuna.

Scientists from the Universities of Leeds and Princeton in the US studied the directions in which different groups of Big Brown bats flew after being released 20 kilometres from their home roost.

Two groups were first exposed to magnetic pulses 5,000 times stronger than the Earth's magnetic field. One pulse pointed the same way as the Earth's field, and the other was in the reverse direction. A third "control" group was not subjected to a magnetic pulse.

Both the control group and the bats subjected to a pulse orientated with the Earth's magnetic field made their way home as normal. However, of those which had been through the reverse direction pulse, only half followed the correct route home. The rest flew in the opposite direction.

Dr Richard Holland, from Leeds University's Faculty of Biological Sciences, said: "This clearly showed that it is the magnetite in their cells which give bats their direction as we were able to change how the bats used it as an internal compass, turning their north into south. But as only half were affected, it's likely there is another mechanism as well, which in some bats enabled them to override the impact of the pulse."

Radio transmitters attached to the bats were monitored both from the ground and a plane to verify their position.

The scientists are having discussions with the American and European space agencies, Nasa and Esa, about using satellites to track smaller migratory birds and mammals.

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