Part 1: North By North-West

Fact: Birds have a built-in compass.

Ever get lost out in the hills and think ‘I wish I had brought a pigeon with me’? Me neither, but turns out they are as good at finding North as any compass.

How birds sense the Earth’s magnetic field – a phenomenon called magnetoreception – is not exatly settled. There are two theories: visual cryptochrome mediated and magnetite compass mediated, both of which are quite the incomprehensible mouthful.

Cryptochromes are a class of protiens that are critical in the eye to see colour. When light hits these proteins they split into a pair of ‘free radicals’: highly reactive molecules which, curcually, are affected by magnetic fields. It is thought that the visual neurons in the eyes of birds are sensitive to these induced changes, meaning these birds may actually see the magentic field of the Earth – for example, as another colour. Think of Alien v Predetor style vision.

Magnetite is a particular form of iron oxide (Fe3O4) – similar to rust, but a lot fancier and more exciting. It is naturally magnetic and found in the beaks of some species of bird: the thinking is that the Earth’s magnetic field might interact with it to produce a physical movement which can be sensed – pretty much using exactly the same mechanism as a compass.

Although both theories could be true – and actually both may be true and work together – the idea of actually seeing a magnetic field is just so much more awesome. Although it does feel a little like the ‘homing’ pigeon is cheating: I could find my way home too if I had a GPS with me.

‘Another one of Mr Shaunak’s Little Bites of Science’
Image under Creative Commons license

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