NatureJun 24, 2021

Magnetic sensitivity of a light-sensing protein in a migrating songbird

Updated Mar 6, 2026

Abstract

Cryptochrome 4 from the night-migratory European robin shows greater magnetic sensitivity in vitro compared to that from non-migratory species.

Night-migratory songbirds use a light-dependent magnetic compass for navigation.
The magnetic sensitivity of cryptochrome 4 (CRY4) is linked to the quantum spin dynamics of radical pairs in the birds' retinas.
In vitro studies reveal that CRY4 from the European robin is more magnetically sensitive than CRY4 from chickens and pigeons.
Mutations in ErCRY4 identify the importance of four specific flavin-tryptophan radical pairs for magnetic field effects.
Findings suggest that sensing and signalling functions in migratory birds could be optimized independently.

Simplified

Night-migratory songbirds are remarkably proficient navigators. Flying alone and often over great distances, they use various directional cues including, crucially, a light-dependent magnetic compass. The mechanism of this compass has been suggested to rely on the quantum spin dynamics of photoinduced radical pairs in cryptochrome flavoproteins located in the retinas of the birds. Here we show that the photochemistry of cryptochrome 4 (CRY4) from the night-migratory European robin (Erithacus rubecula) is magnetically sensitive in vitro, and more so than CRY4 from two non-migratory bird species, chicken (Gallus gallus) and pigeon (Columba livia). Site-specific mutations of ErCRY4 reveal the roles of four successive flavin-tryptophan radical pairs in generating magnetic field effects and in stabilizing potential signalling states in a way that could enable sensing and signalling functions to be independently optimized in night-migratory birds. 1 2,3 4-7

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