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A member on another forum (bjolly) asked me if I'd post a couple of links to some video they shot of this behaviour

YouTube Video

http://www.youtube.com/watch?v=T9CPQnid4xg

YouTube Video

http://www.youtube.com/watch?v=ajzpyOGrZOg

Original forum thread here http://photography-on-the.net/forum/showthread.php?t=816054

Brian V.

EDIT Paul Beuk: Added the YouTube ID's between youtube tags to show the clips in the message.