We’re seeing Blue Jays congregate in groups here, probably for protection (more eyes and ears) from raptors that can see them better now that the leaves are down.
These bright birds have their own trick to take advantage of other birds, especially near feeders. They first try to swarm competitors. If that doesn’t work (and it usually doesn’t with Northern Cardinals), they do a very good imitation of a Broad Wing Hawk scream.
That usually clears the area, even though Broad Wings have migrated south. (Brooklin, Maine; Leighton Archive images)