I wonder about the "naturally stable" part in a context of birds though. I don't think they're inherently stable, I think they're masters at stabilizing themselves. I generally equate "very stable" with "less maneuverable", and vice versa. In that context, I'd be inclined to believe birds are so unstable that I would doubt that even computers would be able to "fly" one. We don't have aircraft that can hold a candle to a bird's maneuverability.
Forgive me going back into this one but you do raise a very good point there. The question as to birds being either naturaly very stable or naturaly very unstable but experts at stability control. It's a tough one, but in the same vien as my original post, I don't know how accurate it is to compare the "very stable-less maneuverable" principle we know to be true with our rigid aircraft on living creautres.
Water is much like air to travel through in theory. Many fish are very maneuverable but all fish are natural stable. It does not matter if they have direct control of that stability or if it is just a lucky evolutionary break. Fish are naturaly stable in the water.
I think in the same way, birds are naturaly stable in the air. The fact that their natural instincts are all it takes to learn to fly and control their stability suggests that they are indeed stable in the air, naturaly. They are natural aircraft developed for countless years, they have mastered the art of "very stable-Very maneuverable" and bypass our principle.
Humans are naturaly stable on two feet once they learn to walk. Sure we could argue that we are just masters of balance, but it comes naturaly to us. We don't have to think about the fluid in our ears to balance.
When it then applies to non-living objects such as our aircraft, any stability we modify on an aircraft must be thought about in advance and then put into practice. Proving the machine to be only an imitation of natural stability that required more than instinct to acomplish.
It is a very difficult question to answer though, so I am just enjoying the discussion here is all.