Can non-moral agents have claim to moral rights?

A brief question, to be sure, but one may not answer it quite so quickly. If we consider certain animals or plants to be without moral agency--that is, if they cannot or do not commit moral or immoral acts, or if they should not be judged morally--can we apply rights (conditional or otherwise) to them as we generally do to humans?

Can we allow such creatures (which may include the severely retarded, infants, and comatose among humans) moral consideration without assuming they have moral rights? If so, is there a good argument to be made in favor of others following us in doing so?

I have found it easier this quarter to remain impassive and judge each view or philosopher on its merits than to posit many of my own stances in response. I suppose this is what is expected of me as an undergraduate student of the discipline, but my aim has never been to become a historian of philosophy or even merely a critic. I believe this is a field in which one must typically be involved in order to progress.

So it is that I posit these questions to myself and others without much concern for my own recent readings in various environmental ethics and open the floor to any with a mind to comment--though I suppose that mostly means myself.