Sort sol

Sort sol (Danish for "black sun") is a natural phenomenon that occurs in the marshlands of southwestern Jutland, Denmark, in the spring and autumn. It involves enormous flocks of European Starlings ( Sturnus vulgaris ) gathering in the hours before sunset.

These flocks, sometimes numbering hundreds of thousands, or even over a million birds, fly in complex, coordinated formations across the sky. The dense formations can obscure the sun, creating a darkening effect that gives the phenomenon its name. The starlings gather in such massive numbers primarily as a defense mechanism against birds of prey, such as hawks and falcons. The dense flocks make it more difficult for predators to single out individual birds.

The 'Sort sol' typically lasts for between 20 and 30 minutes and the spectacle is dependent on weather conditions and the presence of suitable roosting locations, typically reed beds in the marshlands. The peak seasons for observing Sort sol are typically mid-March to mid-April and again from mid-September to mid-October. Guided tours are often offered during these periods to provide optimal viewing locations and expert commentary.