Silhouetted people watching a murmuration of starlings (Sturnus vulgaris). A murmuration is a huge flock of starlings, which typically forms in the evening as they come to their communal roost. Flocks may contain over a million birds. The behaviour is thought to be a defence against predatory birds such as sparrowhawks. Filmed near Sunbiggin Tarn in Cumbria, UK.