sentence: Many migratory animals use the magnetic poles when they travel long distances each spring and fall.
sentences_before: It shields the Earth against harmful particles in space. The field is unstable and has changed often in the history of the Earth. The magnetic field creates magnetic poles that are gradually moving toward the geographical poles.
sentences_after: The magnetic poles will trade places during a magnetic reversal.
concept_name: migratory animal
headings: Earth's magnetic field
categories: Earth Magnetism