We have mockingbirds here who also dive-bomb people who come too near their nests. They are amazingly fierce!
Mika, the USDA zone designations are based solely on the average low winter temperatures so really have not a whole lot to do with the general year-round climate, just "how cold does it usually get?". I am originally from British Columbia, Canada and the hardiness zone in Vancouver is also zone 8 because although it never gets terribly hot, it also never gets terribly cold either.
People have a general perception that "Canada is cold" too. Well, it is cool and damp for a lot of the fall, winter and spring and can be chilly enough to wear a jacket even in the summer just like the UK. I only go back there for visits in August.
