As I recall, it was just flexing momentarily, perhaps preparing to take off due to disturbance from the photographers clustered around it! I have several other photos of this individual, and the wings are held flat. I was going to post one of those, but I liked the composition of this one the best.

I wondered if this were "anti-obelisking", since they use that to compensate for high temperatures. In my experience, they often squat down like a fly when I get too close, prior to taking off.