Lots of luck.

Yes it looks messy and that isn’t our windowsill but ours looks just the same.
You might ask why, well, for the last 3 summers we have been lucky and honoured enough to have House Martins nesting. Apparently the 3 nests have been there for quite a few years and I love watching them. I would have taken a photo of them. Ok I’ll be honest who am I kidding, there isn’t a hope of taking a pic of these acrobatic little birds. Therefore their poo will have to do.