They seem to have a particular liking for this pylon.
Then all at once they fly off to begin the dance. Thousands more fly in to join the group.
It begins as a sinuous back and forth cigar shaped movement which goes on as the light fades.
Eventually the shapes get more and more complex.
At last they dive down into the roost in almost complete darkness an hour after sunset.
Then it is back to the car to try to thaw out my fingers.