Norway Rats digging under snow

Had a client today show me where rats have been raiding her birdfeeder and retreating into a huge ground hugging juniper. Sure enough I see tunnelling through the ground cover and the surrounding grass. She then shows me what she believes is digging caused by rats. Sure enough there has been something excavating dirt in several places and since we just lost our snow it was surely done under the snowpack but there was not a defined hole in most cases....Looked similar to a mole mound to me. Have any of you ever seen mounding like this under the snow by rat?

Thanks,
Chip

These are some of the giants I got around my birdfeeder in my backyard. No males just females though.

Yes, I've had some that looked like groundhog mounds with a smaller hole. Should be some worn out runs with that mess. When I find a location like that I bed traps in runs with no bait. If there are more than one entry point in a 3 foot radious I bed traps infront of the holes, while leaving one hole undisturbed. When I bed traps at locations like that, I leave just the hammer, kill zone and pan exposed. Whack'em and stack'em all day long on them setups. Most times bait isn't needed. If the bird feed is what they're after I'd sprinkle it over bedded traps. Usually I just use bait when placed along an object, or in a open area.