I tried butchering a couple more of them and they didn't even produce skins (only skulls.) Is that even possible? Adult Foxes not giving up skins from butchering? I don't think I've ever heard of the butcher's skill level impacting whether a skin would be produced or not, but it was done by a non-rusty skilled butcher!
There just isn't enough skin on a fox to be usable, just like with kittens.
Were the foxes bought from traders? Because I hear merchant-bought animals can't breed.
Nope, these were captured in my forest and bred successfully (for a while at least.) I do have a two of them I bought off elves, floating around. I'm surprised that there's not enough skin to produce a skin, mostly because I always seem to get one off the kittens and had previously produced two skins from some foxes. It was only the recent batch that didn't produce any. Perhaps it was only a fluke and I should try again. I still have a decent fox population; I guess I can spare a few more of the older ones
FOR SCIENCEEDIT: Well, that's one mystery solved. The latest slaughter produced a skin. So I guess it's up to chance...
EDIT2: After noticing that a number of the animals on display in my zoo were in-fact just a bunch of corpses, I've instituted an emergency breed program for the 4 female wolves and 1 male wolf left. I can only wonder if non-tame animals roaming in a small room within my fortress will actually reproduce or not.
Edit3: A Moody Weaponsmith just produced a Platinum Mace worth 198,000 called The Fork of Obeisance. Not often I have to look up a word, but I did this time! It means "a movement of the body expressing deep respect or deferential courtesy, as before a superior; a bow, curtsy, or other similar gesture. "