Looking at the last few blogs, it seems as if we've had a really short season, with numbers by about the 25th really low. In most places we agree about the peak being between the 8th and 12th. In a private wood in Bucks where I saw at least 20 [32 sightings] in one hour on the 11th, one week later the numbers were down to single figures , and yesterday, two weeks later, I saw none [but found two eggs a few days old]; so, in the last two weeks the numbers have declined dramatically in Upper Thames. Yesterday, however, in two small neighbouring woods in Oxon, the Campbells, saw 6 on the three territories. The concentration is high in these two woods, making it easier to spot them, especially as, year after year, they are very loyal to their high point territories.
The season in UT started properly on 30th June [I discount the two extraordinary sightings far apart on 14th and 15th June], so it will have lasted barely one month ; normally, it is about 6 weeks.
Matthew puts the rapid decline down to a mixture of high winds and poor weather after the peak.