The Arctic tern may be the fittest bird on earth. Every year, it flies
all the way from the South Pole to the North Pole and back again—the longest migration of any bird.

 

With an annual flying distance of around 70,000 kilometres, it is
not surprising that Arctic terns spend most of their lives in the air.

 

They also spend most of their
lives in daylight. They migrate
from summer in the Arctic (where the sun barely sets) to summer in Antarctica (where the same thing happens). That means Arctic terns experience very little darkness.

 

Arctic terns are sociable birds that live and migrate in large groups. Just before they migrate, the group of birds suddenly become very quiet.

 

Every few years, large numbers of Arctic tundra lemmings can be seen throwing themselves off cliff tops and into oceans—where they drown! This extremely unusual behaviour has led many people to believe that, every now and then, lemmings decide to end their own lives. This is not true.

 

Scientists believe that the lemmings’ strange behaviour stems from the fact that they are extremely successful at living in the tundra. Because of that, every few years their environment becomes overpopulated. When 
this happens, thousands of lemmings swarm in all directions in search of less crowded places to live.

 

Eventually, large groups of lemmings reach the sea. Having often crossed lakes and rivers to
get there, the lemmings think they can dive into water and swim to the other side. Unfortunately, they soon find that the other side of the ocean is too far for them to reach!