I have lived in Frome for about 10 years and there has always been around 30 house martins nesting on the houses in the area. This year there are non a few we're around in early may but went after a couple of days. Houses still have old nests attached but empty a number have fallen down from the eaves.
Other than the odd swift in the evening the sky's are empty of martins and swallows its quiet and sad to see
We had 80 Swifts arrive in Coleford last night and there were still a fair amount here at 6am this morning. The previous highest count this year has been in Single figures! Normally a typical number would be 50+
So far I am aware of 7 Swifts nests here (around 20 down on a typical Summer count) but there will usually be more than I am aware of.
We have quite a few House Martins nests but the take up this year has been later than normal. Numbers are down for sure, maybe 50% down I guess.
Swallows have fledged from a couple of nests at the back of the House but these are a recent addition after a lawnmover shed was constructed!
I am unable to comment with any "estimated accuracy" (contradiction in terms!) on the local Swallows.