Adult Red-tailed Hawks generally tolerate juvenile hawks in their territories in the fall but start be aggressive with juveniles once the days start getting longer in the winter.
Today, after watching the adult male of Tompkins Square Park begin to do some hunting, all hell broke loose as a youngster came into the park. Soon both adults were chasing the youngster around the park and calling loudly. I wasn't able to capture the action very well, since it was late in the day and I only had a 600mm lens with me, but it was exciting to see.
This was the hawk causing all of the commotion.