Willow Warblers are slim, delicate birds of woodland, scrub, parks and gardens. They can be heard singing a melodious, warbling song from amongst the tree canopy. Willow Warblers are migratory birds, breeding in Europe and migrating to southern Africa for the winter. They are unusual amongst birds in that they moult all their feathers twice a year – once at their breeding grounds and once at their wintering ground. The reason for this is unclear. Like other warblers, they are insectivorous but will eat berries and fruit in autumn.