It sure sounds like voles! Get thee to a farm store like Agway and buy some
bait called Just One Bite. It comes in 2 forms. One is in envelopes like
mouse bait but the type that is better is in a hard bar. Get some PVC pipe
long enough to stick up out of the snow and stay upright and sink it into the
snow right above the vole activity. Drop one of the bars down the pipe and
cover the opening of the pipe with a cup or coffee can. I may have a photo to
illustrate this better. I'll post it to pixlist if I find it.
Whatever you do...Get after them!
Carol in CT z6/5