W F1/2, impending rain, humid, 8/8 low cloud, QNH 1016 falling.
BS rang me whilst I was in the supermarket doing the shopping! to say that there was a big move of Swifts in progress over Foxhill, Queensbury, W Yorks. At 1900hr more than 150 in the sky at one time all moving whilst feeding and working SW. Birds were at all levels, low and high. Shortly after 1900hr it started to rain (widespread and moving up from the south) and the movement stopped possibly deflected along the front edge of the advancing weather? By the time I got out of the supermarket it was also raining where I was so couldent check the skies.
Estimated at least 500 Swifts > SW