It's all in the beak: scientists find secret of homing pigeons' magnetic maps

The sensitivity of a homing pigeon's beak could provide an answer to the complicated story of how it finds its way home.

The sensitivity of a homing pigeon's beak could provide an answer to the complicated story of how it finds its way home.

Scientists have shown for the first time that homing pigeons have organs at the base of their beaks that map changes in the earth's magnetic field.

The findings lend further weight to the idea that homing pigeons and other migrating birds use a plethora of visible and invisible cues to guide them over hundreds, and sometimes thousands of miles of terrain.

Cordula Mora and colleagues at the University of Auckland believe they may have solved one of the most enduring mysteries of the homing pigeon - whether it uses anomalies in the earth's magnetic field to build a map of where it is.

Although previous experiments have suggested the birds are able to orient themselves according to the direction of the earth's magnetic field, other experiments have failed to show that they can detect subtle changes to the field. A competing theory is that pigeons use an acute sense of smell.

Professor Tim Guilford, of Oxford University, said that animal navigation such as pigeon-homing remained a mystery in several respects. "Birds are known to use the sun as their predominant compass, and nocturnal migrants at least also have magnetic and star compasses. That's stage two, but the cues involved in the 'map' stage, stage one, have proved harder to unravel," he said.

Dr Mora and his colleagues in New Zealand have found that pigeons can detect and, therefore, chart subtle changes in a magnetic field. "This study shows that pigeons have a magnetic intensity sensor, probably in their beaks, which they might be able to use to fix position," Professor Guilford said.

Dr Mora and colleagues say in the journal Nature: "Here we demonstrate that homing pigeons can discriminate between the presence and absence of a magnetic anomaly in a conditioned choice experiment."

The researchers trained pigeons to jump on one of two feeding platforms depending on whether a magnetic field was switched on or off. When tiny magnets were placed at the base of the birds' beaks, or when they were injected with a local anaesthetic, this ability to discriminate between magnetic field anomalies was lost.

The scientists suggest that the birds may have microscopic magnetic particles in their beaks. Changes in the direction of these particles could be transmitted to the homing centres of the pigeon's brain.

There is little doubt that the birds also use visual cues. Earlier this year, Professor Guilford found that homing pigeons taking a familiar route home followed landmarks. His study shows that pigeons rarely travel "as the crow flies" because they frequently follow roads.