The western deer mouse only exists as a separate name because of a 2019 genetic study. Researchers found enough divergence within what used to be one wide-ranging species, Peromyscus maniculatus, to split it into an eastern group and a western group, and North Dakota animals on the western side of that line now carry the name Peromyscus sonoriensis. In the field it looks essentially identical to its eastern relative, so this is a split you’d need genetics, not a glance, to confirm.
North Dakota’s record is thin: 52 GBIF entries and a single iNaturalist observation, 53 total, the last one logged in August 2024. Sightings peak in July, fitting typical late-summer small-mammal activity, though a sample this small says more about limited survey coverage than a real seasonal pattern. Lake Sakakawea is the one location with an actual tallied record, alongside J. Clark Salyer and Chase Lake national wildlife refuges as places with suitable habitat nearby.
No NatureServe state rank has been published yet for this species in North Dakota.
Full species profile
