Notable Audubon Quote: What is the Source?

Inspired by an article on quotations that I found in the buzz log, I discovered the following quote attributed to John James Audubon by zaadz:

A true conservationist is a man who knows that the world is not given by his fathers, but borrowed from his children.

That's a lovely sentiment, and we all want to believe that Audubon would have said something like that. But did he, really? Well, a Google search certainly leads one to believe that he did, yielding nearly 300 sources attributing this quote to Audubon. The trouble is, none of these online sources provide an exact citation to any of Audubon's writings in which the quote appears.

Turning to Audubon's two most recent biographers, we find that the word "conservation" is listed just twice in the index of William Souder's Under a wild sky and not at all in Richard Rhodes's John James Audubon: the making of an American. Souder's reference to Audubon and conservation is perhaps telling:

Audubon's zest for killing wild animals is jarring to modern sensibilities, especially to people who cannot reconcile hunting with the idea of conservation--the latter a cause now closely associated with the name Audubon. Today, most hunters consider themselves conservationists, and their sport has become an essential tool in the management of game and in raising money to preserve wildlife. But Audubon was a premodern man. He hunted, as everyone did then, to put meat on the table. He also hunted for sport. . . . He recognized and often speculated about the impact overhunting could have on wildlife populations. But he was never deterred. He sometimes said a day in which he killed fewer than a hundred birds was a day wasted.

If Audubon really did pen those words about "A true conservationst," as we are led to believe, then he was truly a man ahead of his time, and no doubt more attuned to reality than many of today’s political leaders who refuse to acknowledge the reality of imminent environmental threats such as global climate change.

My challenge to you, dear reader, is this: find a reference (title, page number, etc.) to one of Audubon's journals, letters, or other written works in which this exact quote is found. Let me know what you find.