Migratory birds look like a & # 39; sixth sense & # 39; in navigation that is infinitely better than humans – so that they can find their way to their nesting places.
But exactly how they do this has long confused scientists.
To let a bird know roughly where he is in the world – and to correct himself if he gets off course – he needs a so-called "real navigation".
This means that it can determine its latitude and longitude in one way or another.
The longitude problem – the coordinate indicating an east-west axis position on the Earth's surface – proved insoluble until the invention of accurate clocks.
The Eurasian Reed Warbler, pictured, can navigate using a natural phenomenon called declination. The bird calculates the difference between the magnetic north and the true north to feel how far the east is
Sailors at sea could calculate the longitude based on the difference between their local time and the time in Greenwich, England.
A study of a migratory bird, the Eurasian Reed Warblers – revealed the answer.
The reed singers, who spend the summer in the UK, use a handy trick to navigate – by somehow measuring the variation between the true north and the magnetic north.
The small brown birds benefit from a natural phenomenon called declination.
While a compass needle points to magnetic north, this is not the real north – the North Pole.
Depending on where you are, the magnetic north is one or more degrees further east or west of the north pole.
By taking into account the difference between the magnetic north and the real north, the reed singer can feel how far the west or east is.
The reed singer can sense this difference – known as declination – and use the information to plot the longitudinal point on Earth.
The way reed singers, however, remains a mystery, but the birds can use declination to determine their equivalent in length, the researchers found.
In this way they keep themselves in the right direction during their fall migration from Russia to Africa.
Dr. Richard Holland, from the University of Bangor in Wales, said: "How birds have solved the longitudinal problem has been a scientific mystery.
"It seems that a bird as modest as the reed warbler has a geographical map or memory with which he can identify his longitudinal position on the globe, only by detecting the magnetic north pole and its variance to the real north.
"This, in combination with other external signals, including the strength of the magnetic field, star positions or odors, enables it to determine its current position and orient itself during a long migration."
Dr. Holland's team conducted tests on 15 adult Eurasian reed singers who were about to start their migration from Rybachy, Russia.
The captured birds were temporarily held in small funnel-shaped cages that could be used to record their orientation movements.
Under normal circumstances, the reed singers pointed in the right direction to North Africa. They were then subjected to an artificial magnetic field that was adapted to simulate a deviation from true north that was equal to the amount of declination observed in Aberdeen.
The birds repositioned themselves as if they had been magically transported to begin their migration from the Scottish city 900 miles away.
Dr. co-author Nikita Chernetsov, from the Rybachy biological station in Russia, said: "We have shown for the first time that magnetic declination can be part of the magnetic navigation map, at least with some migratory birds over long distances."
The findings were reported in the journal Current Biology.
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