Another thought was that my new neighbor was doing some sort of craft project and was a bit messy. After all, they had placed a sort of flowing curtain to hang in front of their door, and maybe this was just who they were. And they hadn't cleaned up. So, I swept things away. Though the next day, there was a little bit more.
It was then that I looked up.
And between our two apartments is a light fixture, where I saw this --
Yes, there is a bird nesting there. The leaves and twigs were obviously all brought there to build the next, which is probably occupied for a good part of the day, unless it goes flying off to forage for food. One thing I've noticed is that when it's there, it doesn't move a muscle. You can be three fit away, talking and it just sits there, unmoving. I don't know if that's simply the way a parent bird sits when nesting its young -- or if if thinks if it doesn't move that those people folks around it won't notice that it's there -- or maybe it's terrified. But when I've sneaked a peek silently from my door and looked up, and there's no one around, it still just sits there and doesn't move.
My neighbors had a theory about why the bird built the next there. After all, there are a lot of trees facing this view that would seem to make a great place for a nest. But the thing is, there have always been a squirrel or two leaping their way through those trees, and they've been there for years. Because of the location of this light fixture, far enough away from the trees and having a protective overhanging, angled eaves, this would seem to be a particularly safe place to be.
Though when the light goes on at night, it must be tough to sleep.
And yes, that's my neighbors' curtain hanging down on the right.