Migrating birds seem to have a ‘sixth sense’ at navigation infinitely superior to humans – so they can find their way to their nesting grounds.
But exactly how they do this has long perplexed scientists.
For a bird to know roughly where it is in the world – and correct itself if it goes off course – it needs what is known as ‘true navigation’.
This means it can somehow work out its latitude and longitude.
The problem of longitude – the co-ordinate that specifies an east-west axis position on the Earth’s surface – proved unsolvable until the invention of accurate clocks.
The Eurasian Reed Warbler, pictured, is able to navigate by taking advantage of a natural phenomenon called declination. The bird works out the difference between magnetic north and truth north to sense how far east it is
Sailors out at sea were able to calculate longitude from the difference between their local time and the time in Greenwich, England.
However a study of a migratory bird, the Eurasian Reed Warblers –- revealed the answer.
The reed warblers, which spend summers in the UK, use a neat trick to navigate – by somehow measuring the variation between true north, and magnetic north.
The little brown birds take advantage of a natural phenomenon called declination.
While a compass needle points to the magnetic north, this is not the true north – the North Pole.
Depending on where you are, magnetic north is either one or more degrees further east or west of the north pole.
By taking into account the difference between the magnetic north and true north, the reed warbler is able to sense how far west or east it is.
The reed warbler, can sense this difference – known as declination – and use the information to plot its longitudinal point on Earth.
However, the way reed warblers do it remains a mystery, but the birds can use declination to work out their equivalent of longitude, the researchers found.
In this way, they keep themselves pointing in the right direction during their autumnal migration from Russia to Africa.
Dr Richard Holland, from the University of Bangor in Wales, said: ‘How birds have resolved the longitudinal problem has been a scientific mystery.
‘It seems that a bird as unassuming as the reed warbler may have a geographic map or memory that enables it to identify its longitudinal position on the globe, only by detecting the magnetic north pole and its variance from true north.
‘This, combined with other external cues, which may include the strength of the magnetic field, star positions, or smells, enables it to locate its current position and orient itself during a long migration.’
Dr Holland’s team conducted tests on 15 adult Eurasian reed warblers about to start their migration from Rybachy, Russia.
The caught birds were temporarily held in small funnel-shaped cages that could be used to record their orientation movements.
Under normal conditions, the reed warblers pointed themselves in the correct direction towards North Africa. They were then subjected to an artificial magnetic field adjusted to simulate a variance from true north equal to the amount of declination seen in Aberdeen.
The birds re-positioned themselves as if they had been magically transported to begin their migration from the Scottish city 900 miles away.
Co-author Dr Nikita Chernetsov, from the Biological Station Rybachy in Russia, said:’We’ve shown for the first time that magnetic declination may be a component of the magnetic navigational map, at least in some long-distance migratory birds.’
The findings were reported in the journal Current Biology.