It's mice, I can almost say that for certain. Every time we hit a warm spell (say just about freezing), the mice are a plague. Once a week I help a fella check a very large trapline about forty miles from town. I noticed that Ward always thumped the martin boxes before he peered over into them to check the bait. Never really asked him why. I found out the hard way last weekend. Looked into a box only to have a mouse almost run up my nose! Actually, it was jet black and pretty small so it might have been a shrew. You definitely DO NOT want to get your face very close to one of those vicious, fearless little devils! Use something for bait with more bone too it. Mice can't carry off the bone and even if they clean it, there is usually enough scent left to attract something. Good luck.

Might be weasles. A size 120 conibear killer trap will nail them. What size are you using and how big is the box? Even larger animals will get nailed with a 120 or a 220 (same size with stronger springs). A month ago we picked up a nice lynx that stuck his head in a 120 size box. Crushed his skull. Make your box about two feet long and to exact dimensions of the cocked traps. Place the bait in the middle and a trap at both open ends of the box. Slots for holding the conibear trap don't need to be more than an inch or two into the box, that way the larger animals can get their face into it far enough to get snapped. We seem to get more weasles in the tree-mounted vertical martin boxes. Pretty little things this time of year but not worth a whole lot.

Are your traps getting sprung? If that is the case it may be a coon reaching in and then able to pull himself free. Coons have only just arrived in this country and we haven't trapped any yet but I would say that they probably have the intelligence, dexterity, and strength to extract themselves from a leg-hold trap. Cats won't do that. They're too wimpy. If caught by just a toe, they'll sit there till they freeze to death. If you're using leg-hold traps, I strongly suggest switching to conibear killer traps. They are not only more humane, but also almost faultlessly effective.

Lots of places on line sell conibear type traps. You can find them at Cabela's too (although those guys won't get another dime of my money - I won't help finance an outfit that supports parceling up and selling off the last tracts of hunting land in the US that's still accessible to public). Here's a link: http://www.cabelas.ca/store/?section=1190&section2=1326&section3=1505

Anything that gets into a conibear trap is going to get killed - cats & dogs included. You can find lots of instructions on the net on how to set up a conibear tunnel trap above ground so that at least the dogs will have difficulty getting into one. It's virtually impossible for a dog to get caught in a conibear placed in a martin box. This type of set is also good for other species of fur-bearing critters, particularly mink and weasels. Doesn't sound like coons are your problem. Probably weasels. Go with 120 size. They are strong enough to hold a coon if he tries to reach in. Usually they will at least stick their nose in the tube/box/tunnel first to get a smell. If set properly that will be enough for conibear to nail him dead!