Help identifying mouse-like rodent in Willamette Valley (Oregon)

Question

I live in the Willamette Valley region of Oregon, USA. A few days ago I noticed these rodents digging in my compost pile. This was in the early-afternoon. If I got too close (closer than 4 ft) they would retreat to a pile a branches and trimmings.

The compost pile is well composted and over a year old. I'm not sure what they were eating, but there wasn't any un-composted kitchen food (unless some seeds remained). Squirrels may have hidden something in the pile. There are plenty of worms in the pile.

They have a white underside, the eyes aren't overly large. The coat is brownish-gray. I couldn't see any color variation on the tail. My pictures are low resolution, but I didn't notice large hairs on the tail. I'm guessing the body is about 3" - 4" long.

Here's a list of rodents in Oregon. It seems like the ones in that list that look similar live east of the Cascades. I'm west of the Cascades.

Answer 1

I'm not 100% certain, but they look like a young Rattus genus. They could also be Mus genus (common house mouse) - most of these genera are pretty similar with a pale belly and darker dun dorsum. Young rats superficially look like mice, but have shorter, thicker, and less tapered tails. In both the tail in these is nude (i.e. no long hairs) and is "scaly". Despite their depiction in most popular culture, they are not nocturnal, but rather more crepuscular and active in shortish periods throughout the day and night.

Rats in particular are known to burrow extensively for food and living space, whereas mice tend to occupy already created cavities in areas where these are readily available (i.e. anywhere humans occupy), but will burrow in open areas.