I've heard that areas with a lot of predators, especially hunters, birds will stay roosted a lot longer than normal. Theory I heard was they're waiting to see the hen walk under them so they can fly down to her.
Had a pair of very late season birds do this to me in Georgia, only much later. I think I moved on them 3 times before I spooked them, and only then did I realize they were still in the tree. If memory serves me, it was around 8 when they flew.