Solved, the mystery of how migrating birds plan a route

THE mystery of how birds navigate thou- sands of miles may finally have been solved.

For a bird to know where it is in the world – and to correct its flight path – it needs to know its latitude and longitude.

Now a study of Eurasian reed warblers has revealed how their internal compass works. The birds, which winter in the UK, navigate by measuring the variation between true north and magnetic north.

Depending on where you are in the world, magnetic north is either one or more degrees further east or west of the North Pole.

By taking into account the difference, the reed warbler is able to plot its longitudinal point on Earth. Dr Richard Holland, from the University of Bangor in Wales, said: ‘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 came up with their theory after testing 15 reed warblers in Rybachy, Russia. Their findings are reported in the journal Current Biology.