Migration

Migration is the seasonal movement of a population of animals to a different environment, most common in certain species of birds - such as Arctic terns, which migrate annually 17,600 km between their breeding ground in the Arctic circle and the Antarctic. Migration is also observed in mammals such as porpoises, fish like eels and salmon, and some insects. Birds' migration is fascinating and it is based on their high metabolic rate, which means they require a rich, abundant supply of food at frequent intervals. Birds employ sighting - using landmarks and geographical features like rivers, coastlines, and mountain ranges. They also monitoring the Earth's magnetic field, apparently with their visual system and with tiny grains of a mineral called magnetite in their heads. Birds also observe the stars, use the Sun for guidance, rely on their sense of smell, and may follow their neighbors.