"Can animals be moral?" Well, as opposed to what? To being immoral? Or simply amoral? Are we asking whether animals sometimes do things that have good consequences for others? (Can animals be good utilitarians?!) Or whether they reflect upon the universalizability of their own principles? Or whether they have principles (utilitarian or otherwise)? Is the question whether other animals can do what’s truly right (or moral)—at least what we take to be the truth? Or just whether other animals have a sense of right and wrong (which might be more or less correct in comparison to the ideal, or our, moral standard)? How different could their sense of right and wrong be from our own before we could no longer recognize their “code of conduct” as a moral system of which they are the agents? Or is any code of conduct that regulates social interactions a moral system (descriptively speaking)? What kind of a grip must their morals (or norms) have upon them, in order for them to count as agents, rather than, say, instruments, of the system? That is, to what extent must they understand what they themselves are doing? How much autonomy is necessary? How much reflection? Is it actions that count, or intentions? Reason or emotions? Does moral agency require a “theory of mind”? Does it require a theory at all? Do we require more of potential animal moral agents than we do of the proverbial virtuous peasant? (Or do the virtuous peasant and some animals happen to share the clearly lamentable fate of not living up to our highest rationalistic conceptions of moral agency?)
That, from a paper I am working on, for this. No wonder philosophers have generally preferred just to say that animals are not "moral agents" or "moral beings," etc. That's just a whole lot easier than trying to answer all (or even some) of those questions!