How do you know but that every bird that cleaves the aerial way is not an immense world of delight closed to your senses five?I'm not sure that this can be taken seriously as a question. Or at least as a "How do you know...?" question of the usual kind. There isn't any question of knowing such a thing. Or is there?
Coetzee says that Balcombe argues that:
by dint of attentive observation of the everyday activities of animals, particularly those that are "like" us, we can to a degree come to see the world--our common world--through their eyes and thus to a degree experience, vicariously, "their" world.My sense is that Coetzee agrees, but he doesn't come right out and say so (as I recall). I think I agree too, although the words "to a degree" are important.
How do we ever see the world through anyone's eyes or know what life is like for them? By observation of what they do and what happens to them, and by listening to what they say. If "language is things we do" then there is no very sharp distinction between what people do and what they say, and this sounds right. As soon as we accept that birds and bats are conscious (which is if anything before we are even aware that there are such things as birds and bats--it isn't, that is, something (else) we sign up to believe at the same time, nor something we only come to believe later) we accept that they are like us to a degree. We know what bird fear and hunger are like because these cannot be, it makes no sense to suppose that they are, anything but some form or other of fear and hunger, and we know what they are like. We don't know what it's like to have in-built sonar, but that's pretty much an app we don't have. We do know what it's like to have apps though. (I don't, because I don't have that kind of phone, but that isn't a metaphysically or epistemologically interesting fact.) [Update: and I do have senses, of course. Not that we can just say that if you know the five senses then it's easy enough to imagine another one. That's not true. But knowing what something is like means either having experienced it or else being able to imagine it well. (I'm not sure about this.). And imagining something is not creating in one's mind out of nothing the what-it-is-like of the something in question. It's a sort of mental acting. And I can act like a bat about as well as I can act like another human being.]
So to some extent I know what it's like to be a bird, much as to some extent I know what it's like to be French or pregnant. I haven't experienced these things, and I should be careful about when I claim to have any such knowledge (not, e.g., if the French are undergoing some national trauma, or in the presence of a woman who is having a very difficult pregnancy). But no conscious experience is a completely black box to me or to anyone else. All consciousness is related to all other consciousness, and all intelligibly conscious life is related to every other kind of conscious life. The details are expressed through behavior and language. As someone once said, "Nature is a language--can't you read?"
Of course the "to a degree" part needs to be emphasized. But I think it's important that it's a question of degree. There is also a sense in which each of us is a world of our own, unknowable by any other. But that goes for people I know well just as much as it goes for bats.