Ron Reagan had a column on foie gras recently. Someone then pointed me to Guillermo's site, www.sonomafoiegras.com, as an example of the pro-foie gras argument. Sonoma Foie Gras describes how it lets ducks run around free-range, until they're old enough for the feeding tube. It also says that ducks naturally gorge themselves before migration, implying the tube is just an acceleration of that.
If you're going to market yourself to consumers who avoid cruelty, do it all the way. Let them run around free, and when it's time to bulk up, let them gorge naturally. (It would cost more, but then foie gras is already a luxury.) You could hang up "Bon Voyage" signs to heighten the ducks' sense of impending migration. Then, after they gorge themselves, to avoid being misleading, you'll have to put all theducks on a truck and drive them around the block a few times before they "return home".
