upper thames report 4

It is definitely not over yet; not including this amazing season, we are normally happy if we see up to 5 in an hour or two in one of our woods; on various days this July, 16 were seen in Doddershall Wood, 9 in Chinkwell Wood, and 18 in Bernwood Forest. The total sightings are approaching 250, which is more than twice as many as ever before in the UT.
Today, 5 were seen in Waterperry Wood, including one tatty female with large bits out of her wings, but she still managed to put on a very graceful 'low-level glide show' to delight us.
Question: is it so, that, on one occasion in one place you can see a lot of activity, but one day, or even one hour later, you see either nothing or far fewer?
We have at least two examples: on the 14th of July, in a small wood, where only 2 or 3 had been seen in previous years, at least 9 were seen in various parts of the wood. The wood was visited the very next day, in high winds, and only one was seen. In Bernwood Forest on July 4th, 9 were seen in very active mode along a 300m stretch of ride, while, on the way back 45 minutes later, only one was seen along this stretch.
Why?