While most rehabilitators have little difficulty identifying common species, we often misidentify species that are presented less frequently. Many mice admitted to centers are simply labeled as "field mouse" - a rather generic term applies to any various mouse-like species found in open areas. There is no actual species called a "field mouse." However, accurate record keeping and optimal care-giving mandate accurate species identification. To help you identify that occasional tricky mouse, the following information was distilled from the Peterson Field Guide, A Field Guide to the Mammals, North America north of Mexico.
Mice are members of the order Rodentia, which includes squirrels, beaver, woodchuck, etc. In Ohio, there are 15 species of mice (and mouse relatives) that are represented by three families.
The family Cricetidae includes 10 species in Ohio: eastern harvest mouse, deer mouse, white-footed mouse, eastern woodrat, southern bog lemming, boreal redback vole, meadow vole, prairie vole, pine vole, and the muskrat. The most frequent admissions to rehabilitation centers are likely to be the following four members of this family: 1)Deer mouse, which ranges in color from pale gray to deep reddish brown and has a white belly and feet and a distinctly bicolored tail (dark above and white below). 2) White-footed mouse, pale to deep reddish brown in color with a white belly and feet, but the tail is not distinctly bicolored and it is also usually shorter than the head and body. 3) Meadow vole, usually dark grayish brown with small ears; belly is silvery, slightly buffy, or dark gray; tail is bicolored but relatively short compared to "average mouse." Range of meadow vole overlaps that of other Ohio voles, so always check the field guide. 4) Muskrat, sometimes mistaken for beaver by callers, can be easily distinguished from all other mammals by its long, naked, laterally compressed tail, which shows a distinct ridge along the top of it (compared to the wide dorsoventrally compressed beaver's tail).
Jumping mice are in the family Zapodidae. There are two Ohio species: 1) Meadow jumping mouse, and 2) Woodland jumping mouse. A mouse from central Ohio with an extremely long tail and large hind feet will most likely be a meadow jumping mouse. If the mouse comes from northeastern Ohio, check the field guide because it could be either species. The woodland jumping mouse usually has a white tail tip.
The Old World rats and mice belong to the family Muridae and are represented by three introduced pest species in North America: 1) Black rat (AKA roof rat), 2) Norway rat (AKA brown rat or house rat), and 3) House mouse (AKA Mickey or Minnie)> The rats and mice used as food sources by some rehabilitators for their patients and educational animals are laboratory strains of the Norway rat and house mouse. Wild strains of these rodents vary from dull grayish brown to black and have long, naked tails that are fairly uniform in color. The house mouse is distinguished from deer or white-footed mice by its belly color (gray or buffy) and the tail (naked, scaly, and uniformly colored). Compare tail lengths to distinguish between the black and Norway rats. The tail of the black rat is longer than its head and body. In the Norway rat, the tail is shorter than its head and body. The naked tails of these two rats make it easy to distinguish them from a similarly sized eastern woodrat, a state endangered species. The tail of the eastern woodrat is furred and bicolored. Additionally, most woodrats prefer to live in remote areas, away from urbanization, so they are unlikely to take up residence in someone's garage or attic.
This guideline covers most "mouse issues" likely to occur, but it is far from complete. Having good reference materials on hand is encouraged. They not only will help with identification, but can also help with natural history and diet information so that the rehabilitator can provide quality care.
~Rebecca Stillwell is an OWRA member and a rehabilitator who volunteers at Wildlife Haven.