Subspeciation in the Meadow Mouse, Microtus pennsylvanicus, in Wyoming, Colorado, and Adjacent Areas

A detailed look at the meadow mouse across the high plains of Wyoming, Colorado and nearby states reveals a surprisingly intricate pattern of colour variation. The author begins by outlining the traditional split between two recognised subspecies—one pale, the other dark—and notes puzzling gaps in their reported ranges. Early observations hint that populations in the Big Horn Mountains look more like the pale form, while those further west and south lean toward the darker type, suggesting a more complex mosaic than previously thought.

To untangle this, the study adopts a hands‑on approach, selecting representative skins and assigning them a simple five‑point colour scale. By examining dozens of specimens from museums and field collections, the author charts average colour scores on a map, exposing geographic trends that point toward additional, distinct groups. The work offers a clear, method‑driven path for anyone interested in how subtle traits can illuminate the hidden diversity of a common, yet understudied, rodent.