Natural vis a vis unnatural

At what point does the natural world end and the unnatural world being? Is at your front doorstep? Your driveway? Your fenceline?

One possible distinction between natural and unnatural is that what is nature is what would exist if man had not, and what is unnatural is what exists because man does. Thus, the doorstep is an unnatural object, it is manmade, of course. What of the bird's nest then? Why should the same distinction not apply? What is natural is what would have existed if the bird had not, what is unnatural is what exists because the bird does. Thus a bird's nest is a "birdmade object". But the common perception, I think, is that the bird's nest is natural whereas the skyscraper and the B-52 bomber are all unnatural.

What say you who believe the B-52 is unnatural to the fact that birds drop coconuts upon rocks in order to extract the innerds? Does the evil of a B-52 taint its distinction as manmade and thus unnatural? You who believe such are truly misanthropic.

What of the skyscraper? How is a skyscraper any different from a birds nest (other than the irrelevant size difference)? A set of materials, tendentiously moved from their natural place and from their natural shape into a new form with new purpose. Is this a good definition of both a skyscraper and a bird's nest? If not then why?

Does conscience and conscious choice make the difference? How egotisictical must we be to say that we, mankind, are the only entities on this planet who do not exist merely in a state of responding to stimuli and nothing else. Conceeded: an ant responds to stimuli and nothing else; but what of dolphins? They blow airbubble circles and then float through them. They exert energy to do things which have a purpose other than pure survival and these actions cannot be explained simply by stating that they are responses to stimuli.

Thus, what makes one thing a natural object and another an unnatural object. All manmade objects are made by a reorganization of natural objects, there is no possible way to make anything else, thus all things are natural objects and the destinction between natural and unnatural is fleeting.