Oh, yeah, those mockers are territorial. We have one that chases the crows away. Good for it! Once I heard the "hit" as the mockingbird hit the crow in the backside. OW! I have also seen them chase HAWKS! Gutsy little things. Their song can be beautiful or ugly. Eight months pregnant and one took up residence. The thing had an ugly noise...and knew when I got up in the AM. It would not stop...even with the drapes closed and tiptoeing...it knew when I got up! My sympathies to those of you who have to listen to the ugly noise instead of the pretty song.
To scare a crow away, clap your hands...they don't like the sharp sound.