Re: duck mount issue
Bugs will eat whatever is most convenient first. Foot webbing is the easiest and quickest and usually shows damage first. Haired mounts like deer, foxes and coyotes usually take longer to start showing damage. A good indicator is finding what looks like fine sawdust under the mount or the larval "shells" on the floor and possibly in the hair itself. Two years is really not that long when it comes to a bug infestation. It often takes several years for a bug population to establish itself enough to do serious damage but thy WILL get everything unless you get them first. Like I said, look for sources of contamination like home taxidermy items, uncleaned deer skulls, turkey tails, etc or your pet food. They came in somewhere and it wasnt on a mount.
The other possibility is mice. Mice will eat the feet, toes and webbing of birds and then go away. Mouse droppings usually give them away.
Good luck in your eradication efforts.