I found this bathroom tray with some curiously placed dry grass and feathers, then it hit me that a bird thinks it's found a new home!
When you think about it, the shape of the tray lends itself to the kind of form the bird needs to build a cosy nest. The apartment is high up over the ground level and the place is yet to be occupied, so it makes sense why the bird 馃惁 thinks it's an ideal place to raise a family.
I haven't seen it in action though, it may leave through the open window long before I get into the room to check.
I'm guessing it won't be fair to let it build only to destroy it later, maybe also the eggs if any. Better to force it to look elsewhere for an ideal residence.