Each autumn — primarily October and November — the marshlands around Tønder host one of Europe's most extraordinary natural spectacles: vast flocks of starlings performing their murmuration, known locally as "sort sol" or "black sun." Hundreds of thousands to over a million birds move together in dense, rapidly shifting formations that momentarily block out sections of the sky before the flock descends into the reedbeds to roost.
The best viewing is an hour before sunset in the marshlands south and west of Tønder toward the German border, particularly around the village of Højer. Local guides and guided viewing trips operate during the season. The birds are most reliably present from late September through November; October is usually the peak. Dress warmly and bring binoculars — the flocks can shift position rapidly.