This was posted at Carnivore Conservation blog. It links to the latest data (in papers). It is from a 2004 symposium, which was badly needly because the publicly available information was a decade old.
About the recovery of the Black-footed Ferret. (corrected link)
Like the wolf, the ferret’s endangered status is the result of the livestock industry which hates prairie dogs, the sole prey of the ferret. They don’t like the fact that the prairie dogs “steal” a little grass and make holes their slow-witted cows stumble on.