when they care about animals it's as a side effect of virtues whose primary purpose is to facilitate > cooperation and peace between humans (and caring about animals is a good way of signaling those virtues).

Hmm. Last I checked, I do care about animals, regardless of signalling -- indeed, I often take a bit of a signal-hit when people see me help beetles safely across a street, or spend time cosing up to an orangutan through the glass at the zoo (thereby rendering him less-viewable by the other patrons, even though he's primarily responding to a familiar presence and displays no interest in anyone else).

There's very little sense of signalling virtue -- I'm not a vegan or vegetarian, I don't adhere to any religion with specific rules about the treatment of animals; I certainly don't find it to enhance my cooperation with other people (some people admire it, but an awful lot of them find it a bit weird or kooky).