golden plover display flight

[ChrisJB]

I was up in the northern Yorkshire Dales last week and whilst at one of the black grouse sites, I found myself more fascinated by the display flights of golden plovers. I have seen stacks of golden plover on territory, the full length of the Pennines, but have never seen this before. They were flying quite high, and demonstrated two wing beat patterns. One was the typical fast wader-like flapping, which was followed by a spell of a stiff winged, almost butterfly-like flight pattern. On the fast one (I think) the birds warbled loud and fast. But were silent on the 'stiff flight'.
Has anyone else seen this? A pal of mine said he saw one doing it on the moors near Stoodley Pike (between Tod' and Hebden Bridge) one evening a few years back.
I've searched the WWW and not found much on it.

Chris