The Arctic Tern's Migration

The difference between night and day is dramatic - so dramatic that most species of animal can thrive either in the day or in the night but not both. They usually sleep during their 'off' period. Humans and most birds sleep by night and work at the business of living during the day. Hedgehogs and jaguars and many other mammals work by night and sleep by day.

In the same way, animals have different ways f coping with the change between winter anc summer. Lots of mammals grow a thick, shaggy coat for the winter, then shed it in spring. Many birds, and mammals too, migrate, sometimes huge distances, to spend the winter closer to the equator, then migrate back to the high latitudes (the far north or far south) for the summer, where the long days and short nights provide bumper feeding. A seabird called the Arctic tern carries this to an extreme. Arctic terns spend the northern summer in the Arctic. Then, in the northern autumn, they migrate south - but they don't stop in the tropics, they go all the way to the Antarctic. Books sometimes describe the Antarctic as the 'wintering grounds' of the Arctic tern, but of course that's nonsense: by the time they get to the Antarctic it is the southern summer. The Arctic tern migrates so far that it gets two summers: it has no 'wintering grounds' because it has no winter. I'm reminded of the joking remark of a friend of mine who lived in England during the summer, and went to tropical Africa to 'tough out the winter'!

The bird migrates back and forth from North and South poles so that it always enjoys the arctic and antarctic summers.