Birds are able to sense magnetic fields and use them to navigate. However, this capability for magnetoreception is light-dependent; without blue light, birds are unable to orient to a magnetic field. The blue-light-sensitive cryptochrome proteins CRY1 and CRY4 have been shown to play a role in birds' magnetoreception. Research published in 2018 argues that CRY4 proteins in bird retinae are responsible for this sense, which previous research has shown to be coactivated with ascending visual pathways.
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