Earth鈥檚 north magnetic pole is moving from Canada towards Siberia. Has there been a noticeable effect on migrating animals that sense the geomagnetic field as a navigation aid?
Mark Thompson
Tewkesbury, Gloucestershire, UK
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For any animal that is using a magnetic field for long migrations, they may be using it only to detect deviations from their planned route. It has been proposed that migratory birds, for example, have at least three different compasses at their disposal: one allows them to extract information from the position of the sun in the sky, another uses the patterns of the stars at night and the third is based on Earth鈥檚 magnetic field.
Once they are under way, their magnetic sense would help keep them on the course planned using their other senses, again not because they were born with a genetic geomagnetic map of Earth in their brain, but rather by the simpler mechanism of steering to minimise changes in their orientation relative to the field.
Thus, a slow geomagnetic movement wouldn鈥檛 be a problem 鈥� the migrating animal wouldn鈥檛 care at all which way the field is pointing or whether it used to be different. They would only care that they stayed in the same orientation to the field that they sensed when they began.
We know Earth鈥檚 magnetic field has flipped several times during the evolution of birds, and there is no evidence this has caused mass extinction events.
Steve Agar
Nine Banks, Northumberland, UK
Having for many years considered how ludicrous some bird migrations are, I do wonder whether they have been victims of evolution acting more slowly than the rapid 鈥渇lips鈥� of Earth鈥檚 magnetic field from time to time.
Rather than weeks-long transoceanic and transcontinental flights, perhaps the poor blighters were originally simply setting off on a short sojourn south to feeding or breeding grounds far closer to home.
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