KEY POINTS:
A peculiar glitch in the Earth's magnetic field has been used to demonstrate how pigeons, dropped off hundreds of kilometres from home, are able to navigate back to their lofts.
Todd Dennis, of the University of Auckland, said yesterday: "We are now confident pigeons do use the intensity of the Earth's magnetic field to determine position during homing."
He led research published in the Proceedings of the Royal Society that shows homing pigeons use the strength of the Earth's magnetic field to sense how the field around them is changing and work out where they are relative to home.
Dr Dennis released homing pigeons in New Zealand's own "X-files" spot - the Auckland Junction Magnetic Anomaly, an area where the Earth's magnetic field is naturally distorted - to test whether the anomaly confused the birds' ability to position themselves. A cluster of massive rock slabs deep below the surface in Mt Roskill causes a detectable spike in the geomagnetic field.
On release, the birds flew up to 4km in the wrong direction, parallel or at right angles to variations in strength of the local magnetic field, before redirecting themselves towards their loft.
This discovery will settle a long-running debate over whether pigeons navigate by smell or through an ability to read Earth's magnetic fields. Some birds are known to use the sun as their predominant compass, and migratory birds that fly at night are known to navigate by stars, but the use of magnetic fields has proved harder to unravel.
In 2004, other scientists at the university showed pigeons were capable of using the same magnetic "sixth sense" as fish to find their way home - tiny deposits of a mineral called magnetite, or lodestone, in their beaks.
The mineral is in the same part of the body, and uses the same nerve to connect to the brain, as in trout, stingrays and a bird called the bobolink.
In the latest research, researchers fitted the pigeons with tiny global positioning system (GPS) devices and found that the geomagnetic anomaly threw the birds for a loop.
Of the 92 pigeons released around the anomaly, 59 clearly flew relative to the direction of the local magnetic field - not the Earth's field.
As soon as they escaped the bounds of the anomaly, the pigeons corrected their direction and headed directly home.
Dr Dennis said this showed the birds kept track of gradients in the magnetic field to navigate.
California Institute of Technology's Joe Kirschvink told sciencenow.com the experiment was "fantastic".
- NZPA
