An absence of Mockingbird has been a sadness for your correspondent. I see one now and then, they look a little shy, they go through the motions, harp on a little, try a couple of calls, test the air, might even chase someone and then they are gone. Of the theories there are many, one of which lays the blame for Mockingbird absence on the male Brown Thrashers' ability to give Girl Mockingbirds the creeps. I've called it "The Dirty Old Man Theory of Mockingbird Absence."
It's an interesting theory, probably needs years of study and to be taken
seriously will require a quantum shift in the position our species holds with
respect to other species. Still there is hope in an algorithm that mimics what
we rather grandly call Human Intuition. I read about this algorithm somewhere in
one of those "happy-happy how cool are boffins type news outlets" which don't
actually tell you anything and as usual I dismissed it as being well paid for by
those advertizing interest that are still trying to sell me an electric train
set. My lesson I suppose is never search U-tube.