Light-dependent magnetoreception in birds: the behaviour of European robins, Erithacus rubecula, under monochromatic light of various wavelengths andintensities

To investigate how magnetoreception is affected by the wavelength and inten sity of light, we tested European robins, Erithacus rubecula, under monochr omatic lights of various wavelengths at two intensities using oriented beha viour as an indicator of whether the birds could derive directional informa tion from the geomagnetic field. At a quantal flux of 7x10(15) quanta s(-1) m(-2), the birds were well oriented in their migratory direction east of N orth under 424 nm blue, 510 nm turquoise and 565 nm green light, whereas th ey were disoriented under 590 nm yellow light. Increasing the intensity of light at the same wavelengths more than sixfold to 43x10(15) quanta s(-1) m (-2) resulted in a change in behaviour: under bright blue and green light, the birds now showed a preference for the East-West axis, with the majority of headings at the western end; under bright turquoise light, they oriente d unimodally towards a direction slightly west of North. Under bright yello w light, the birds continued to be disoriented. These findings suggest a rather complex relationship between the receptors involved in magnetoreception. Magnetoreception appears to follow rules that are different from those of vision, suggesting that light-dependent magnet oreception may involve receptors and neuronal pathways of its own.