They're baby mice. We carefully replaced the top part of the log that had been covering them. When we checked on them the following day, they had gone - hopefully mommy moved them to a new location. We do have garter snakes, and other predators, however, so they could easily have been eaten as well.
I'm not sure which species our mice are. They are grey with a slightly lighter grey undercoat. They don't seem to match any of the pictures I find on the local wildlife websites. They live outside - underground and in the wood pile and occasionally come into the house in the spring to find food. Our current cat has been an excellent deterrent, so we haven't had any food stolen for the last 2 springs.
Local resources with information about wildlife:
- Burke Museum Mammals of Washington
- Washington Nature Mapping Program