Black sun is a natural phenomenon that can be seen when migrating starlings gather in large flocks to overnight in the reeds.
Just before the starlings settle down for the night, the huge flocks create fascinating patterns in the sky that almost obscure the light of the setting sun, thus leading to the phenomenon being given the name "Sort Sol" - the black sun.
The starlings come to the marshes to feed on the larvae of crane fly and garden chafers, which are found in their greates abundance in the wet grasslands. During the day, the birds search for food in the outer polders of Tønder marshes, whilst at night they overnight amongst the reeds. The areas in which they spend the night are constantly moving in order to avoid the attentions of birds of prey and because the reeds will break after a few days, thus leaving the starlings with their feet dangling in the water. It’s therefor impossible to know exactly where the starlings will settle for the night.
The starlings’ spring migration lasts from February until the middle of April, whilst the autumn migration begins in August and may last right through to December. If you wish to experience the phenomenon, you can head out on a Sort Sol safari in the Tønder marshes.