We have partnered with Durham University on their Public Engagement in Science module this year and this blog was produced by a student as part of their work towards the module.

 

Many bird species migrate, often to breed or to find food, but have you ever wondered how birds navigate? How do they find the same places each year?

There’s no definite answer; one theory suggests that birds use the Earth’s magnetic field.

The Earth has a magnetic field, which is like a bar magnet, with magnetic poles near the north and south poles. The magnetic field allows a compass to work and shows the direction towards the north pole. The presence of the Earth’s magnetic field means that if animals had a “compass” inside them, it could help them migrate.

Image of Earth showing magnetic field lines 

The Earth's magnetic field lines. Image Credit: www.dkfindout.com

Several metals are magnetic, of which iron is the most common. This means that iron will respond to the Earth’s magnetic field and iron rich parts of a bird that are susceptible to magnetic fields could help them navigate by detecting the strength and direction of a magnetic field.

The parts of a bird that could be susceptible to magnetic fields varies across each species. Here are three examples:

  • Upper Beak - Some species have a magnetic iron compound in the top of their beak.
  • Inner Ear - An organ in the inner ear, the lagema, has high levels of iron
  • Eyes - Some species detect changes in the direction of the Earth’s magnetic field in their eyes. Chemical reactions in the eye are then affected sending signals to the bird’s brain, telling it in which direction to go.

However, magnetism is not always used alone in migration. Research has shown that birds can detect magnetic fields less accurately when the sky is overcast compared with when it is clear, this would imply that they use other methods of navigation too such as landmarks and the position of the Sun.

Some of the birds which have migrated to Saltholme this spring will have used these methods and will use them once again when they return south in the autumn.

Two common terns passing a fish between their beaks. 

Common Terns. Image Credit: Mark Hamblin

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