Animal Migration

Each year billions of animals undertake journeys that dwarf any human voyage, crossing oceans and continents with astonishing precision. Arctic terns fly from pole to pole, while monarch butterflies travel thousands of kilometres to forests none of them have ever seen, guided by instincts encoded over many generations. Scientists once puzzled over how creatures with tiny brains find their way, and the answer turns out to be a toolkit of senses. Many migrants read the position of the sun and stars; others detect the Earth's magnetic field, using it like an invisible map. Some salmon even memorize the chemical signature of the stream where they hatched and follow it home years later. Migration is risky and exhausting, but it lets animals exploit food and breeding grounds that appear only at certain seasons.