animal burrow under raised garden

A couple weeks ago, I noticed these holes under my raised garden bed. They definitely weren't there when the snow melted (although I did have a bit of vole damage on the grass adjacent to the raised bed), since I didn't see them when I mowed the lawn a few weeks back.

Any idea what these could be? I think I'll have to dig up the raised bed and put chicken wire at the base before I start planting anything this year..

Thanks!