The six House Martin nests in the eaves of our house have had an exceptional year, but one nest is STILL feeding two nestlings, as yet unfledged. This is possibly a third brood from that nest. All the others (around 30) have headed south. Interestingly there are three adults busy feeding the young which are very close to fledging, so perhaps one from an earlier brood has remained behind to help the parents with the feeding which is getting somewhat frantic! At least the unseasonal warmth is providing food.
This is the latest departure that I can ever remember.