I don’t think that a Mockingbird ever met a Blue Jay that it did not despise,  however they apparently become more discriminating among other creatures.

A friend of mine once told me about a Mockingbird nesting in his yard.  The bird appeared to undisturbed by his cat, but mercilessly harassed strange cats that came near  the nesting area.  It was like my friend’s cat had some kind of property rights.