The pigeons probably use tiny magnetic particles in their beaks to sense our planet's magnetic field, scientists say

The birds use their ability to create a map of this field and then use it to navigate back to their home loft, New Zealand researchers claim.

It casts serious doubt on a theory that the birds use smell to navigate.

Cordula Mora and colleagues from the University of Auckland, New Zealand, placed homing pigeons in a wooden tunnel with one feeder platform at each end of the tunnel.

Attached to the outside of this tunnel were magnetic coils.

The pigeons were trained to go to one feeder if the magnetic coils were switched off and to the other if the coils were switched on.

Homing sense

The scientists then carried out tests designed to impair their ability to detect a magnetic field.

Firstly, they attached magnets to the birds' beaks, their ability to discriminate when the magnetic coils were switched on or off was drastically impaired.

Secondly, the Auckland team anaesthetised the upper beak area of the pigeons, a similar drop was seen in the ability to detect the magnetic "anomaly" generated by the coils.

Finally, the researchers cut the pigeons' trigeminal nerve (a large nerve carrying optical and other signals to the brain) and found that their magnetic sense was again impaired.

However, this did not occur if the researchers cut the olfactory nerve (which conveys smell signals to the brain), contradicting the theory that they navigate using smell.

Taken together, these results are consistent with the theory that homing pigeons detect magnetic fields using particles located in their upper beaks.

The existence of these magnetic particles in the birds' beaks has been known since the 1970s.

"We suggest that our work provides the basis for detailed studies of both the operation and use of the magnetic sense in homing pigeons and possibly migratory bird species," the researchers write in Nature.