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 ...