New knowledge about the navigation of migratory birds

The discovery, made with the help of funding by the Lundbeck Foundation, may be relevant for the development of the next generation of supercomputers – so-called quantum computers.

One question that has been keeping biologists busy for some time now is how migratory birds use the Earth’s magnetic field as a compass, enabling them to navigate accurately when flying at night.

Over the years, many theories have been debated, and new knowledge has now emerged.

In an article recently published in the scientific journal Nature, an international group of researchers demonstrated that a molecule in the retinas of night-migratory birds – which, it has been suggested, is a “compass molecule” – is actually magnetically sensitive.

The migratory bird used in the study is the robin (Erithacus rubecula); a bird very common in Denmark.
However, DNA analyses show that the light-sensitive protein investigated (CRY4) in the study is also found in the retina of other night-migratory birds.

The hypothesis that a particularly light-sensitive molecule in the eye of a night-migratory bird could be the key to a biological function enabling the bird to use the Earth’s magnetic field as a compass was first suggested in 1978 by the German biophysicist Klaus Schulten.

‘And we’ve developed his idea further,’ explains Henrik Mouritsen, biologist and professor of neuroscience at the Carl von Ossietzky University of Oldenburg, Germany.
Professor Mouritsen and his colleague Professor Peter Hore, from the Department of Chemistry at the University of Oxford, UK, headed the scientific study.

Their work received funding from a range of sources, including the European Research Council, the US Air Force, Deutsche Forschungsgemeinschaft (DFG) and the Lundbeck Foundation.
One of the researchers involved in the study is Ilia Solov’yov, a 2014 Lundbeck Foundation Fellow. Today, he is professor of physics at the university in Oldenburg.

DNA analyses provided the answers

To elucidate CRY4 – the protein in the robin’s retina which the researchers presumed to be the key to understanding the bird’s creative use of the Earth’s magnetic field for navigation – it was necessary to obtain a certain amount of the protein. And this is not something you “just do”.

However, because by now they had deduced the sequence of the bird’s DNA that produces CRY4, the researchers were able to insert this code into bacteria and subsequently mass-produce the protein.

The protein samples were sent to the University of Oxford, where they studied the 527 amino acids that make up CRY4.

Quantum mechanical calculations showed that four of these 527 amino acids, acting together with a vitamin molecule, are presumably behind the potential magnetic properties associated with the protein in the robin’s retina.

And this hypothesis, partly based on Ilia Solov’yov’s calculations, proved to hold water when it was tested in the lab.

When the four amino acids and the vitamin molecule were exposed to light, so-called radical pairs were formed, consisting of two unpaired electrons. These radical pairs were then subjected to a magnetic field.

‘In our opinion, these results are extremely important, because they show for the first time that a molecule in the visual system of a migratory bird is sensitive to a magnetic field,’ says Professor Mouritsen.

The hypothesis is, therefore, that the same thing happens in the eye of a robin and other night-migratory birds – and that this helps them find their way.

‘But we won’t be able to say this with 100% certainty before we’ve tested the hypothesis on the eye of one of these migratory birds. The problem is how to perform such an experiment. And we haven’t yet worked this out,’ Professor Mouritsen explains.

If it can be proven that the response seen in the laboratory mirrors what happens in the eye of a night-migratory bird, it could have implications for the development of the next generation of supercomputers – so-called quantum computers, designed to handle huge volumes of data.

If so, we will have access to vital information about a quantum mechanism that enables animals to register extremely weak signals in their surroundings.
These signals are up to one million times weaker than the weakest signals animals have thus far been thought to be able to sense.