Yesterday morning, I saw a group of c125 House Martins gather over my street, then fly out of view in a sort of westerly direction. It was raining quite hard at the time. I presumed that 'my' local breeding birds would be among them, and that would be the last I'd see of them this year.
However, this evening, about 30 of the locals were still hunting for insects above the houses as normal. When will they depart? Where will they go when they do? How many of them will come back next year? Nobody knows.