This video says about itself:
Short film about “murmurations”: the mysterious flights of the Common Starling. It is still unknown how the thousands of birds are able to fly in such dense swarms without colliding. Every night the starlings gather at dusk to perform their stunning air show.
Because of the relatively warm winter of 2014/2015, the starlings stayed in the Netherlands instead of migrating southwards. This gave filmmaker Jan van IJken the opportunity to film one of the most spectacular and amazing natural phenomena on earth.