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The mysterious ability of homing pigeons to find their way back to their lofts from distant and unfamiliar locations has long defied scientific explanation. Now researchers claim to have solved the riddle, according to a study published today in Proceedings of the Royal Society B.

Cordula Mora and team from the University of Auckland already knew that there must be enough information at a site where a pigeon is released for it to find its way. That's because even birds who are taken to the release site under anaesthetic can fly back home. So what is it that guides the pigeons back from so far afield?

Previous suggestions have included sense of smell, but the answer seems even more simple they rely on the earth's magnetic field, says Mora: ' Pigeons respond to the earth's magnetic field at the release site when deciding on a flight direction. 'Scientists refer to this method of orientation as the map-and-compass hypothesis' where pigeons first identify where they are relative to the loft, then guide themselves home. 'Our results imply that pigeons use the earth's magnetic field for determining their position at the release site before laying a course for home,' say the authors, who obtained the results after a careful analysis of pigeon's flight paths from over 100 release sites in Germany.

The results also help explain another mystery why it is that pigeons often fly off in the wrong direction when they are released. The researchers showed that this was no random act the pigeons simply followed the contour lines of the earth's magnetic field.

Very few studies have managed to show a link between magnetic fields and the direction pigeons fly in when released, says Mora. 'We showed that flight direction by pigeons shortly after release is strongly and systematically related to variations in the earth's magnetic field with pigeons following magnetic intensity slope or contour lines at the release site before vanishing from view.'