There were TWO robins in there! Both of them must have been there for a while and they were SO tired and frightened. They each sat very still while I took their picture ... then I realized that I could probably just reach out and catch them to put them out the door.
That's exactly what I did. One at a time, I pinned each robin against the window, got a firm grip on it, and I carried it to the door and let it go. (Unfortunately, you'll have to imagine what this looked like because I couldn't hold the bird AND get a picture of it.) I looked all over and didn't find any sign of a nest ... they must have been in there hunting bugs.
Now I know why they call them 'bird brains'