Bobby is seated on the right, Violet on the left.
I don't know what they were noticing but they were doing so at the same time:
Bobby walked to and then behind Violet, switches places with her.
In this photo below, it looks like they're communicating, doesn't it?
Bobby walked further along to the left-hand side of the building top:
Violet, alone, was soon harassed by a mockingbird:
He sat on this perch for about half an hour, enjoying a preen during part of his visit:
... and touched down for an elegant landing on yet another favorite perch, atop an American flag on an NYU building at the East end of the park:
After at least an hour and a half of watching him relax on this perch, I had to end my visit and make my way home. I stopped and turned to take more photos of him from time to time while I walked away. It's tough to say goodbye to a hawk in plain sight!