Some friends pointed me to a Smithsonian article about recent research on fruitbat vocalizations. The upshot is that fruitbats gripe at each other in lots of different ways.
[N]early all of the communication calls of the Egyptian fruit bat in the roost are emitted during aggressive pairwise interactions, involving squabbling over food or perching locations and protesting against mating attempt.
Using algorithms, researchers were able to discern differences in bat griping depending both on who the target bat was (who was being griped with) and the context (what the griping was about).
I have argued that, for a domain of enquiry that includes meerkats in their natural environment, different meerkat alarm calls and the classes of threats which elicit them comprise natural kinds (see ch4). That admits six kinds, because there are three different calls and three corresponding classes of threats.
There’s no reason why the argument doesn’t generalize. For fruit bat groups in their environment, there may well be natural kinds corresponding to distinct classes of vocalizations and to the classes of objects picked out by those vocalizations. But what if it turns out that bat reference to individual other bats uses sounds functioning in the fashion of proper names? Suppose there’s an individual bat that the other bats pick out with a specific squeeky sound, something like “leeko leeko leeko”. Does that individual bat count as a natural kind?
One might think the answer has to be no, because kinds and individuals are different ontological categories. I’m not tempted by that, however. As I argue, species might turn out to be continuous individuals (in their fundamental ontology) but still count as natural kinds (see ch6).
Nevertheless, the category for the specific bat leeko could only be a natural kind for the domain including that specific bat population. And it might lack enough general importance to be a natural kind for a domain that includes all the Egyptian fruit bat populations across both space and time. So my account doesn’t require the answer to be yes.
Moreover, it’s not clear to me from the recent report whether the distinctions between bat vocalizations are clear and sharp enough to count as natural kinds. As always, the answer will depend on the details.