Thanks to Jenny for sending in this wonderful picture of Starlings flocking above Gretna Green motorway service station in late November. Apparently starlings do impressions – of a dolphin in this case.
I've never seen a truly massive flock of starlings doing their thing but I understand the noise is also quite something. More pictures of their swooping, wheeling forms via Google.

Aha, a Murmuration of Starlings. I love those birds, so sassy and cheerful. The noise that a Murmuration makes is quite astounding.