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Navigation using Earth's magnetic fields.


 
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Dr Ursula Munro presents startling new findings on how birds learn to make the great migratory journeys that they do and what this means for the rest of the animal kingdom.      


 
Above: photo by Jan van de Kam from page 88 of Life along land’s edge. Eastern curlews, bar-tailed godwits with the local silver gulls on the water line Roebuck Bay. Still aloft are red knots and curlew sandpipers. The migratory travellers come from a range of lands from five to ten thousand kilometres away.

 
Migratory birds make some of the longest journeys in the animal world. How do they do that year in year out, and how do they find their way to feeding and breeding grounds with uncanny accuracy? New research shows that these birds are born with a program which tells them which way to fly. The program seems to use the old navigation techniques of the sun and the stars but the more important imprint seems to be a reaction to the Earth’s magnetic field.     

Laboratory experiments show that birds respond to changes in magnetic fields and use this as a way of plotting their way to feeding and breeding grounds thousands of kilometres away.
This magnetic orientation exists in two separate perceptual systems. The first is in their eyes, meaning that birds actually “see” these magnetic fields, using energy rich short wavelength light. This gives them an accurate magnetic compass as part of their visible spectrum, an extraordinary navigational aid which they use to precision.
Even the low levels of light from stars and moonlight is sufficient.

 
Right: So far ten distinct flyways that shore birds use on their migrations have been identified and are shown on the world map from page 89 of Life along land’s edge.

 
Humans are not good investigative subjects because we have the road signs provided for us, but there is evidence that this tracking system is used by fish, amphibians, reptiles, invertebrates and mammals.
Global positioning suddenly takes on a new meaning.

Text: V.B.


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