I got out to the farm yesterday to find all three scenarios in one place. The vast majority of nests were empty, two had chicks which will have fledged in a few days time, and several contained eggs. Only one of the clutches was definitively cold so there's the possibility that some birds are trying to get one late brood in. I'll go back in a week or so to double-check.
|Over 50 in the air, 1 caught. Result. There were only one pair with a brood in the building, to be fair.|
I don't have short nets to cover exits but did manage to find space for a 12m and caught one adult female while we were there. It wasn't evening and the sun was low, so the nets were far too visible.
There were plenty of swallows feeding over surrounding fields. If I have time I'll try to figure out where they're roosting.