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European Robin Can See Magnetic Field, Literally

July 12, 2010

In 1968, it was first discovered that European Robin can sense magnetic field which helps them in sensing directions and makes navigation easy during migration. Since then scientists have been trying to understand the mechanism. Further studies revealed that it’s the right eye and left part of the brain that is capable of sensing the magnetic field. Light sensitive part of Robin’s retina contains molecules called called cryptochrome and flavin adenine dinucleotide (FAD) which when excited by sufficient amount of blue light shift to active state where they both contain unpaired electron forming a “radical pair” which interacts with earth’s magnetic field and generate shades and even colors which overlay on the regular visual image formed by retina. When the bird tilts head, the shade pattern changes, kind of like compass needle and thus Robin gets precise sense of direction.

In order to study this in detail, experiments were carried out by Katrin Stapput of Goethe-Universitat in Frankfurt and reported in Current Biology. They covered Robin’s eyes with goggles (either frosted or clear) on left eye or the right eye and then they were let fly from a funnel shaped cage. Robins with goggles on left eye had no issues in sensing correct direction. While those with goggles on right eye went random directions. Conclusion from this study was that Robins ofcourse see magnetic fields from right eyes but the vision has to be strong enough from right eye to make them any sense out of shadings. Fuzzy goggles made vision less clearer and hence Robins couldn’t understand much of the shading patterns and lost directions. So just vision from right eye is not important to see and understand magnetic field, but vision has to be strong enough. Here is the abstract of this study:

Abstract: Magnetoreception of Directional Information in Birds Requires Nondegraded Vision doi:10.1016/j.cub.2010.05.070

Katrin Stapput, Onur Güntürkün, Klaus-Peter Hoffmann, Roswitha Wiltschko1 and Wolfgang Wiltschko

The magnetic compass orientation of birds is light dependent . The respective directional information, originating in radical pair processes , is mediated by the right eye . These findings suggest possible interactions between magnetoreception and vision, in particular with the perception of contours, because the right eye has been found to be dominant in discrimination tasks requiring object vision. Here we report tests in the local geomagnetic field with European robins wearing goggles equipped with a clear and a frosted foil of equal translucence of 70%. Robins with a clear foil on the right eye and a frosted foil on the left eye oriented in the migratory direction as well as birds using both eyes. Birds with a frosted foil that blurred vision on the right eye and a clear foil on the left eye, in contrast, were disoriented. These findings are the first to show that avian magnetoreception requires, in addition to light, a nondegraded image formation along the projectional streams of the right retina. This suggests crucial interactions between the processing of visual pattern information and the conversion of magnetic input into directional information.

Stapput’s experiment is the first to show that magnetic sensing does not just depend on light being present as previously thought, but that the bird must have a sharp, focused image in its right eye. The magnetic sensing is overlaid over the normal vision, and if that is distorted, Stapput said the patterns of light and dark would make little sense since the bird cannot separate the information from the visual and magnetic images. The visual and magnetic images both involve variations in light and shade, but visual images tend to have sharp lines and edges, while the magnetic images have more gradual changes from light to dark. The experiments lend support to the radical pair hypothesis but do not rule out another explanation such as presence of magnetite on the beaks of some of the birds. []

Picture credit: Flickr user used under Creative Commons License

Filed under: Research,Science

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