This autumn, dark clouds will gather over the UK's skies.
Far from being foreboding, they herald the start of one of nature's great spectacles.
Over the coming weeks, millions of starlings will take to the air performing a series of breathtaking aerial ballets each evening before dusk.
Such murmurations are a testament to the amazing, complex behaviours that animals are capable of.
Yet scientists are only just beginning to understand how they do it.
Watch a special report on starling murmurations broadcast by BBC Autumnwatch on Thursday 18 November on BBC Two at BST 20.30.