New insight into the light-dependent magnetic compass of birds

Date: June 6, 2016

Source: Goethe University Frankfurt

Birds have a light-dependent compass in their eyes. This compass gives them information about the direction of the Earth's magnetic field. Prof. Roswitha Wiltschko's research group at Goethe University Frankfurt, together with French colleagues, has elucidated how this compass works at the molecular level.

Birds have two sensory organs for orientation and navigation in the Earth's magnetic field: They use their beak to measure the strength of the magnetic field, while their eyes provide directional information. One type of cone photoreceptors in the birds' eyes is sensitive to UV light and also contains a form of the protein cryptochrome. Previous studies of the Frankfurt researchers suggested that most likely it is this protein that enables birds to detect the magnetic field.

A cyclic reaction involving one light-dependent and one light-independent step takes place in the cryptochrome. Two radical pairs are formed during this cycle, and their unpaired valence electrons react to magnetic fields. The Frankfurt group, working in collaboration with Pierre and Marie Curie University Paris, have now discovered which of these two radical pairs is crucial for navigation in the Earth's magnetic field.

In a behavioural study on robins, the birds were subjected to two experimental conditions:

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The magnetic compass of birds is affected by polarized light

Date:January 26, 2016

Source:Lund University

The magnetic compass that birds use for orientation is affected by polarised light. This previously unknown phenomenon was discovered by researchers at Lund University in Sweden.

The discovery that the magnetic compass is affected by the polarisation direction of light was made when trained zebra finches were trying to find food inside a maze. The birds were only able to use their magnetic compass when the direction of the polarised light was parallel to the magnetic field, not when perpendicular to the magnetic field.

"We were expecting an effect, but not one so major that it would lead to complete disorientation when the direction of the polarisation of light was perpendicular to the direction of the magnetic field," says Rachel Muheim, who was in charge of the study.

It is still unclear how the different directions of polarised light in relation to the Earth's magnetic field affect birds in the wild. The researchers have put forward a thesis that the birds use it to accentuate the magnetic field during sunrise and sunset -- times of day when migratory birds are believed to determine their direction and calibrate their compasses before migrating.

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