Fox often Den up near abundant food supplies, if that supply runs out they are going to look for another. If they get near starvation, pretty much anything is fair game.
They can also be lazy and will head for the sure thing. Had a buddy who raised eating Ducks, he had a thousand (if not more), it took one family of Fox three years to clean him out and put him out of business. We eventually figured out the Fox were using the underground drainage system from a nearby interstate to creep in and out of his farm. We were really scratching our heads trying to figure out how the Fox came and went without ever being seen.
In England a mother went into the nursery to see why the baby was crying and found a Fox eating her babies face off.
It is all fun and games, cute little Fox kits playing near the den, until they get really hungry.