I'm just curious to ask anyone who has produced sound for a nature documentary, how much of the audio content is recorded in the field or how much is the product of sound design?
Yes, generally a very large percentage of audio in nature docs is recorded in post. Back in January I posted a TVB Europe magazine article on my blog that deals with exactly that subject.
I know some people who work in that arena and from the stories I've been told that it's a frighteningly large amount... or more than the suits would like us admitting to. I'd say at least 75% in most situations.