Is the body language or vocal expression of, say, a wolf or a chimpanzee symbolic? It’s part of an instinctive habit-system, but its ‘terms’ have very little capacity for growth in either breadth or depth. Nor can they be combined, in the way that symbols can, to make reference more specific or more general. Wolves can talk (and listen) to us, but are not in the habit of talking about us in our absence, in the way that we are now talking about wolves.
From the human side, Farley Mowat communicated with wolves by pissing around his territory. But could he say anything to them about, say, astronomy? As a member of a symbolic species, he could even talk about things and situations that don’t exist, and about whether they could or should exist (modality). Whether this actually raises the level of conversation is debatable – but only in symbols.