Last night I thought they had all fledged but this morning this one stuck his head out.
He stayed like this most of the day, only occasionally pulling back inside.
The adults have been on the nearby wire most of the time, once in a while flying over as if trying to coax him out.
As I write this at 7:30 PM, he is still there.

And, by the way, the swallows have no problem with the entry but the House Sparrows took one look and left.