Birds Use Their Heads to Activate Geomagnetic Sense

OLDENBURG, Germany, November 10, 2004 (ENS) - A group of young researchers has uncovered a key clue to an old and longstanding mystery - how migratory songbirds sense geomagnetic fields and use this information to orient their flight. The new findings document a specific head-scanning behavior, not previously understood, that is performed by the birds just before orienting their bodies toward their migratory direction.

Night migratory songbirds are known to use a magnetic compass to guide them during yearly journeys covering thousands of kilometers, but how these birds detect the reference direction provided by the geomagnetic field, and where the sensory organ for this task is located, has not been known.

In the new work, biologist Dr. Henrik Mouritsen at the University of Oldenburg, and colleagues, discovered that caged garden warblers use movements called head scans to detect the direction of the Earth's magnetic field.

Garden warblers like this one use head scans to orient themselves, researchers believe. (Photo courtesy Dr. Henrik Mouritsen)

In addition, birds experiencing a zero magnetic field appear to search more diligently for the missing reference direction by tripling their head-scanning.

The findings of Mouritsen and his team confirm that the magnetic sensory organ is located in the birds' head.

The fact that head-scanning frequency increases when birds cannot detect the field can be used as a new method to determine the limits of the birds' magnetic sense.

Researchers can expose the birds to a specific magnetic field and ask the birds whether they can sense the field. If they cannot sense it, they will "tell" the researchers by shaking their heads more intensely.

Mouritsen and his group - Gesa Feenders, Miriam Liedvogel, and Wiebke Krop - use mathematical modelling, physics, quantum chemistry, molecular biology, neurobiology, computer simulations and newly developed laboratory equipment in combination with behavioral experiments and analyses of field data to achieve a better understanding of the behavioral and physiological mechanisms of long distance navigation in insects and birds.

They are part of a young research group supported by the Volkswagen Foundation. Their results are published in the November 9 issue of "Current Biology."