Super sensesBirds don't only recognise their route by eyesight. They can also detect infrasound, which is a noise made by sound waves too low for us to hear. The movements of wind or sea against land produce infrasound, which carries a very long way. So migrating birds may be able to hear the landscape long before they can see it. They may also be able to smell distant land or water, and even to ‘feel’ the shape of the land or sea below them by the way it affects air temperature, wind speed and atmospheric pressure. Magnetic attractionMany scientists think that birds have an internal ‘compass’. They have found tiny grains of a magnetic mineral called magnetite in the head of some birds, including pigeons. This mineral can detect the Earth's magnetic field, so it may allow birds to navigate by finding the position of true north. Experiments show that they also use the sun and stars to adjust direction in places where the earth’s magnetic field changes.People’s brains also contain traces of magnetite, and experiments have shown that it helps give us a sense of direction. Blindfolded volunteers were driven to unfamiliar locations. Some had magnets strapped to their heads, which interfered with the earth’s magnetic field. Those without magnets could point back in the direction of home, even when still blindfolded. But those with magnets became completely lost and confused. |
