To many Rainier hunters (foxes, coyotes, bobcats, owls, martens, mink) the deer mouse looks like dinner. These North American mice are only distantly related to the common house mouse, having larger eyes, white bellies, and much greater jumping ability (hence their name).

Wonderland backpackers are likely to encounter them if staying in the stone shelters at Summerland and Indian Bar, which were built by the Civilian Conservation Corps during the Great Depression and have been inhabited by mice ever since. They are notorious for making a mess of improperly hung supplies, to the extent where the bear poles found at Rainier campsites really ought to be called mouse poles! They also sometimes break into cars parked at trailheads, especially if any snacks were left in the car.

Deer mice will nest anywhere from underground burrows to 80' up a tree.

In the western United States, they are the natural reservoir for hantavirus, a rare but potentially fatal disease spread through their feces and urine. Beware if you find mouse droppings in your tent, shelter, or food bag.

In his book "A Year in Paradise", Floyd Schmoe describes a deer mouse called Oscar who lived year-round in the hut at Camp Muir. It is unclear how a mouse could have got there, let alone survived, but there is evidence from elsewhere of deer mice adapting to the harsh conditions of surprisingly high elevations.