If one looks at birds and their behavior every day, they will see trends that no one else comes upon. Since I read a lot of literature about bird behavior (I am better as a researcher than a real birder) I have learned that Chickadees have alert signals to their tribe (to steal a Darwin term for species) about potential peril. They have a signal for ground animals such as cats or raccoons that differs from the signal given if a hawk is spotted. This signal lets their brethren know which way to protect them.
Another article that I read described a study that had students’ deliberately tough Mockingbird eggs in nests on their campus. The study indicated that the Mockingbirds identified the interlopers and dive bombed them as they walked the campus; the birds were able to single out the students specifically and did not bother other students. This went on for several weeks suggesting that the Mockingbirds targeted those that they identified as the interlopers. This in my mind is absolutely fascinating-the study found that the birds were able to do facial recognition. I read this article many years after wondering why I was so harassed by Mockingbirds while on my deck or mowing the lawn. The study suggested that I had somehow encroached their nesting territory. I probably did.
In the house that I have lived in four years now I do a lot of backyard bird observation and have noticed that particularly, House Sparrows take umbrage at the sight of Grackles coming to the feeder in the summer. There are many Sparrows to the infrequent Grackle visitor. So at a ratio of about 20-1 (I did not count exactly) the Sparrows ganged up on the Grackles and in short order the latter just flew off. It simply was not worth the hassle I told myself.
As I arrived home from work this afternoon I heard an irritated chirp coming from a single Robin in my yard. It was long and consistent. I saw that there was a cat in my yard and chose to observe the events. That Robin it seems was making a call to arms as within about twenty minutes I had some twenty or more robins in the yard and they chose to dive bomb the cat who by now was actually cowering. It appears as if they had a sentinel standing guard to let the locals know of this impending peril. The Robins were relentless and the cat stuck close to the ground. Finally it escaped the yard and the activity stopped…until the cat returned an hour or so later. The whole drama replayed itself.
I did not read about this in an article, I simply watched it. I have no studies or statistics to back up my claim but I am confident that like so many other birds, Robins have ways to protect their own (derivatively other species as well) from cat predation. It was pretty impressive and next time I’ll take a video of the event.