Light-dependent magnetoreception in birds: the effect of intensity of 565-nm green light.

In a previous study, Australian silvereyes tested in autumn under monochromatic 565-nm green light at intensities of 2.1 and 7.5 mW m-2 preferred their normal northerly migratory direction, whereas they showed a significantly different tendency towards northwest at 15.0 mW m-2. Repeating these experiments in spring with silvereyes migrating southward, we again observed well-oriented tendencies in the migratory direction at 2.1 and 7.5 mW m-2. At 15.0 mW m-2, however, the birds once more preferred northwesterly directions, i.e. their response under this condition proved to be independent of the migratory direction. This contradicts the interpretation that monochromatic green light of this high intensity leads to a rotation of compass information; instead, it appears to produce sensory input that causes birds to give up their migratory direction in favor of a fixed direction of as yet unknown origin.