Abstract
BackgroundThe Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Under monochromatic light of higher intensity, however, they showed unusual preferences for other directions or axial preferences. To determine whether or not these responses are still controlled by the respective light regimes, European robins, Erithacus rubecula, were tested under UV, Blue, Turquoise and Green light at increasing intensities, with orientation in migratory direction serving as a criterion whether or not magnetoreception works in the normal way.ResultsThe birds were well oriented in their seasonally appropriate migratory direction under 424 nm Blue, 502 nm Turquoise and 565 nm Green light of low intensity with a quantal flux of 8·1015 quanta s-1 m-2, indicating unimpaired magnetoreception. Under 373 nm UV of the same quantal flux, they were not oriented in migratory direction, showing a preference for the east-west axis instead, but they were well oriented in migratory direction under UV of lower intensity. Intensities of above 36·1015 quanta s-1 m-2 of Blue, Turquoise and Green light elicited a variety of responses: disorientation, headings along the east-west axis, headings along the north-south axis or 'fixed' direction tendencies. These responses changed as the intensity was increased from 36·1015 quanta s-1 m-2 to 54 and 72·1015 quanta s-1 m-2.ConclusionThe specific manifestation of responses in directions other than the migratory direction clearly depends on the ambient light regime. This implies that even when the mechanisms normally providing magnetic compass information seem disrupted, processes that are activated by light still control the behavior. It suggests complex interactions between different types of receptors, magnetic and visual. The nature of the receptors involved and details of their connections are not yet known; however, a role of the color cones in the processes mediating magnetic input is suggested.
Highlights
The Radical Pair model proposes that magnetoreception is a light-dependent process
The Radical Pair model of magnetoreception by Ritz and colleagues [1] proposes that directional information from the geomagnetic field is obtained with the help of radical pair processes taking place in the eye
Tests with Australian silvereyes, Zosterops l. lateralis, [6,7], European robins, Erithacus rubecula [8,9,10] and European garden warblers, Sylvia borin [11] revealed that magnetoreception requires light from the blue-to-green part of the visual spectrum: the birds were well oriented in their seasonally appropriate migratory direction under wavelengths up to 565 nm green light, whereas they were disoriented under 590 nm yellow and beyond
Summary
The Radical Pair model proposes that magnetoreception is a light-dependent process. Under low monochromatic light from the short-wavelength part of the visual spectrum, migratory birds show orientation in their migratory direction. Lateralis, [6,7], European robins, Erithacus rubecula [8,9,10] and European garden warblers, Sylvia borin [11] revealed that magnetoreception requires light from the blue-to-green part of the visual spectrum: the birds were well oriented in their seasonally appropriate migratory direction under wavelengths up to 565 nm green light, whereas they were disoriented under 590 nm yellow and beyond In addition to these passerines, a similar wavelength-dependency is indicated for homing pigeons [12], so that it can be assumed to be rather widespread among birds
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