- Cryptochromes and neuronal-activity markers colocalize in the retina of migratory birds during magnetic orientation. Mouritsen, H., Janssen-Bienhold, U., Liedvogel, M., Feenders, G., Stalleicken, J., Dirks, P., Weiler, R. Proc. Natl. Acad. Sci. U.S.A. (2004)