San Francisco breaks out in bird houses

Lately while Walking San Francisco, I seem to be noticing more and more of these structures.

Some are tasteful.

Others appear highly imaginative.

This one might have escaped from a Grimm's fairytale.

This one looks more like some kind of hostel.

These seem designed to bring cheer, even if there are no bird occupants. Indeed, I don't think I've observed any occupied bird houses. Well-populated feeders, yes indeed. Perhaps local birds are less homeless than hungry?