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Robins’ eyes may have in-built ‘compass’

Migratory birds have an uncanny ability to orient themselves, finding their way across sometimes thousands of kilometres between seasonal locales. Especially impressive are those migratory birds that travel at night, often alone.

While it’s been known since the 1960s that birds can use Earth’s magnetic field for guidance, the exact mechanisms have remained elusive.

Seeking to understand this sensory mystery, researchers from Carl-von-Ossietzky Universität Oldenburg, Germany, looked at a type of protein – chryptochrome 4 (CRY4) – found in the light-detecting cells in the retinas of robins, and compared its magnetic sensitivity to the CRY4 proteins found in two non-migratory birds, chickens and pigeons. 

Robins are small, iconic and much-loved birds, seen as symbols of European winters, which migrate in response to food scarcity in the colder months.

As described in a new study in Springer Nature, the researchers found specific mutations associated with the CRY4 protein in robins that may allow them to sense magnetism within their eyes, leading them to hypothesise that robins have a ‘living compass’, and may be able to ‘see’ Earth’s magnetic field to orient themselves.

The authors explain that this works through a mechanism whereby the protein displays a light-driven chemical reaction that triggers quantum effects that can amplify magnetic signals. This happens through a quantum phenomenon known as radical pairs – in which an external magnetic field affects chemical reactions by altering the spin of weakly paired electrons.

The new find is exciting for birders and scientists alike, offering a window into a sensory world humans can only imagine – though the authors caution that further testing of CRY4 while in the eye is necessary to definitively prove whether the birds can ‘sense’ magnetism.

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