In years gone by, I've spent many days snow-tracking marten in Alaska and in Idaho. Amazing what you can learn. One of the neatest things was the fact that they investigate pretty much every leaning tree (thus, I think leaning poles are a natural draw when trapping, even withhout bait). The holes into the subnivean world (underneath the snow) are at these leaning trees, and I think they depend on them for access to food. Also, they catch a lot of shrews beneath the snow, and those shrews are usually discarded (not eaten). I've noticed the same thing (non-use of shrews) by the boreal owls.

Jack