I think this answer to Becky-Jo's question depends on our definition of music, too. I always feel arrogant supposing that humans are the only beings that can do something, even if it's true, because I feel like I'm being elitist, or excluding other valuable beings. But, truthfully, actions and sounds made by beings and things in nature (excluding humans) are dictated by instinct and survival alone; they are not creative expressions of purposefully organized sound.
Perhaps we do need to eliminate human action from our definition of nature, as Becky-Jo found, for this purpose. We make sounds and actions instinctively, too, but not in music. We may sing or hum reflexively, but we've learned to do that in certain instances, and I think that is very different from the purpose and instinct of a birdsong. We may use music as a way to communicate something, but it is not the same instinctive reflex as say, yelling if you are afraid, or in pain, is a way to communicate.
For these reasons, I think music (by our working definition) is indeed a product of humans alone, and as all art, not made by beings and things in nature.
Is singing, humming, playing an instrument (even an invented one,) in any small way, natural? How do we make the distinction between what is music and what is instinctive amongst humans? If we speculate that music is a human activity, is it even important for us to make this distinction?