Aitchison in The Articlate Mammal:
" Even though intelligent animals seem capable of coping with some of the rudimentary characteristics of human language, they do not seem predisposed to cope with them." Language training for apes is, in her eyes, an unnatural task.
What they can do is carry out simple slot filling manouevres, providing they are adequately rewarded. They show no evidence of structure. Chomsky states: "higher apes lack the capacity to develop even the rudiments of the computational capacity of human language."
So, no, Jambo, I cannot agree with this:
"I think the systems of signs used by animals can with some certainty be said to be language, at least by some definitions of 'language', but not all."
For me Language has to be more than a series of bird calls or bee dances - it has to have the capacity to create unique utterances and express that which has never been expressed before. What they do is communicate but I don't think they are using 'language' to do it.