The prothonotary wasn't the only bird in this space. A sapsucker was working the Library trees.
Four hundred pictures shot, time to head uptown. In the park I saw a flock of kinglets working the baseball field, waited for them to chomp closer (the field is fenced off), when suddenly a bluejay flew down, silently, attacked one of the kinglets, flew off, (not with a catch). All kinglets vanished up into the trees. I could hear them, but not see them. It was a real stealth attack, maybe territorially motivated.