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Magnetic compass orientation and polarized light sensitivity in birds

Birds are well known for their impressive migrations and their ability to sense the Earth’s magnetic field and the polarization pattern of the sky, and use this information for orientation and navigation.

The light-dependent magnetic compass is thought to be located in specialized, magnetosensitive photoreceptors in the eyes, enabling birds to perceive the Earth’s magnetic field as a three-dimensional pattern of light irradiance or color variation superimposed on their visual field. Cryptochromes have been proposed as likely candidates for such magnetoreceptor molecules, but the actual receptors have not yet been conclusively identified and located in birds.

Despite of convincing evidence that birds use cues from the skylight polarization pattern for orientation and compass calibration, we know almost nothing about how they can perceive this information. While the polarized light receptors in many invertebrates and some fish species are relatively well studied, birds do not have any obvious receptors in their eyes. Thus, the question of how birds can perceive magnetic field and polarized light information belongs to the major unresolved mysteries in sensory biology.

Our goals are to unravel the mysteries of these two enigmatic senses in birds. We have developed a new behavioral assay where we train zebra finches to locate a hidden food source with the help of directional magnetic field and/or polarized light cues. This assay allows us to examine the behavioral and functional mechanisms of magnetic compass and polarized light sensitivity in birds either separately, or in combination with each other, enabling us to investigate how birds can perceive these two senses.

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