In further addition, here are a few past forum notes on scrapes.
BRI-2012 reply #1
...the nest-called a scrape because the falcon does not actually build a nest, but rather digs a depression in the gravel found on a high ledge, usually a cliff. These birds have adapted to human development by taking advantage of tall man-made structures such as skyscrapers, water towers, or bridges for nesting spots.
Wilmington-2011
Spring is in the air for these two and reports of bonding and making a scrape at the nest box have been observed, as well as canoodling.
U of Alberta-2010 reply #118
... has made a nice little scrape in the nestbox - I think the big event is very close!