We get cardinals doing this behavior. It was really annoying last year, until I hung a sheet over the window. I think the inflatable owls or snakes sound good too. Or murder.
This year we have a small bird who built her nest in our garage. She's got 4 eggs in it, but she is more off the nest than on. And when she's off, she's perched nearby, dropping her mess everywhere. Why do birds poop so much?