Field mice spend much of their lives in warrens of tunnels that they build underground. There they are relatively safe from predators like owls, hawks, and foxes. In winter, when a good, heavy snow falls, the mice can come above ground and build their warrens in the snow itself. Then, when the snow melts, they go underground again. But not without leaving behind a trace of their under-snow warrens.
This winter’s historically heavy snowfall is finally melting away where we live. And here, sure enough, are the meandering trenches that the mice followed to get around beneath the snow.