A Nocturnal Visitor

On Thursday night, just as we were finishing dinner, I noticed my cat Phaedra staring out the patio door, all hunched up with her ears flattened as if she were about to pounce. She typically adopts this posture when watching the squirrels or chipmunks that come up onto our back deck looking for peanuts, but as it was fully dark out I realized that something else must have caught her attention. We have had raccoons come up to our back door at night before (once), but I didn’t think she would see a raccoon as potential prey. When I went over to look, I found this guy instead:

White-footed/Deer Mouse

White-footed/Deer Mouse

It is either a White-footed Mouse or a Deer Mouse, both members of genus Peromyscus. These two species are almost impossible to tell apart unless you have one in your hand. Both are brown above and white below, a colour pattern that extends to the tail. Both have large ears which have little fur covering them and big, protruding eyes.

In Deer Mice, the two colours of the tail are sharply defined, while in White-footed Mice the line between the two is less distinct. Another characteristic which differentiates these two species is the length of the hind feet: Deer Mice generally have hind feet that are 22 mm or less, while White-footed Mice usually have hind feet 22 mm or more. The colour of the fur can also help distinguish these two species, however it is not a reliable trait as these two species have different geographic variations. In general the Deer Mouse has a richer, brownish or tawny pelage, whereas the White-footed Mouse tends to have a pelage that is more pinkish-buff or grayish, with scattered dark hairs.

Both of these mice are excellent climbers, and the White-footed Mouse is known to be a strong swimmer. Both species are commonly found occupying man-made structures such as barns, garages, storage sheds, and even houses. During the winter, the Deer Mouse often travels above-ground, which makes it vulnerable to nocturnal predators; their tiny skulls are one of the most common items found in regurgitated owl pellets.

The mouse appeared to be eating the red peanut skins that the squirrels had left behind earlier that day. I cracked open the door and took the below photo:

White-footed/Deer Mouse

White-footed/Deer Mouse

It got spooked after that, then fled into the night. This was only the second time I’ve seen a mouse feeding in my yard; though Phaedra has been checking the back deck every night since, we haven’t seen it again. Hopefully it survived the cold weather and the snowstorm we had this weekend!

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