It seems as though this happens every morning about this time in an apparent effort to assure that all of the eggs are fertile.
This morning it was particularly quick.
She was sleeping peacefully on her three eggs.
Then she looked toward the box entry.
Then he was on her, as pictured.
Then he was gone.
All in the space of about two minutes.
Some mornings he brings food and/or there is mutual grooming before he jumps her, but not on this visit to the nest this morning.