Mob Scene

Today, on our walk, I was alerted to this hawk by two screeching crows.  The behavior of crows dive-bombing a larger predator is called "mobbing." The crows were trying to drive the bigger bird out of town, or at least out of their part of town. 
 
Mobbing can be seen any time of year, but most often during nesting season. Other times of the year smaller birds can simply move away from an invading predator, but in the spring, most birds have set up a territory and they are obliged to defend it.  See Extra for the rest of the story.