The question of "empathy" and "theory of mind" are distinct. I'm just talking about empathy; Jerry and John introduced the theory of mind stuff into the discussion. I have to disagree with you and Jerry about the definition of empathy; psychologists have studied it for decades. It's the metacognitive ability to understand the thoughts and feelings of another entity. There's plenty of research about personality differences related to empathy and techniques for increasing empathy.
However, every reliable and valid measure of empathy relies on language and the assumption that a person can reflect upon and report their psychological states. This is the methodological problem I have with any attempts to demonstrate empathy in entities that cannot talk.
If my cat brings me a dead bird, should I call that empathy? How could I tell whether or not my interpretation is correct?
I have to say this whole question "Does species X have human characteristic Y?" isn't very interesting to me; it really makes no practical difference whether or not my cat has empathy--I'll feed her and pet her in any case. As I mentioned earlier, given compelling data, I'd be happy to say that some particular species has the capacity for the human experience of empathy. I have nothing invested in the belief that empathy is exclusive to humans.
Miles