The snow in the yard - once nearly four feet deep - has consolidated down to something closer to three feet. Days of sunshine and warmer temperatures have caused slight melting during the daytime, then refreezing at night. This allows the girls to walk on water or sleep on it (as Maia demonstrates in this photo).
Last night, around midnight, I heard the girls run to the back side of the yard. I quickly got out of bed and dashed to look out a window, concerned they might actually step over the top of the fence and give chase to whatever it was they heard. They could easily do so.
I was pleased to see them quietly sitting together, about two feet shy of the fence, looking off into the white-blanketed distance. A half moon illuminated the landscape, but not well enough for me to see what attracted their attention. The deep snow in the field, and the sense of exposure they would surely have beyond the safety of their yard, keeps them inside - guarding me, I like to think.
Or perhaps it was a deer they heard, and they know they've got a "snowball's chance in hell" of ever getting close to one in deep snow. So why bother?