The shape of the birds reveasl the migration distance. For example, birds flying the longest distances are torpedo-shaped. Mallards and lapwings are short-distance migratory birds. They breed in Denmark, but if necessary, they migrate to the coastal areas of Germany and the Netherlands for the winter. Common eider and oystercatcher are medium-distance migrants. They breed in Northern Europe and migrate to Western Europe. Finally, the group of long-distance migrants includes birds breeding in the Arctic, such as the red knot, the black-tailed godwit and the ruddy turnstone, which all migrate to tropical Africa for the winter.
Travelling with oxygen
On their daily flights, birds usually stay close to the coast, but over longer distances migratory birds travel at high altitudes. Small birds, such as the snow bunting, fly at heights of one kilometre above the ground, whereas the dunlin, the black-tailed godwit and the lapwing travel at altitudes of four to six kilometres. Larger birds, such as geese, cranes and storks, can fly at altitudes as high as six to nine kilometres above the surface of the earth. Birds flying at such high altitudes have to use their oxygen better than other species, such as humans. Therefore, the birds bring their own oxygen. Some species of birds have up to nine air sacs that connect to the lungs, but they can also use their hollow bones to store oxygen.
Migratory birds not only use the Wadden Sea as a pantry. In the spring and the autumn, millions of feathers can be found on the salt meadow. Feathers wear out after travelling halfway around the globe, and the birds need new plumage to continue their journey.