A MOUSE IN THE HOUSE:
WHICH Peromyscus IS WITH US?

Okay, let's face it. We live in out the Carolina Piedmont countryside in a charming old farmhouse built nearly a hundred years ago. It's got some delightful eccentricities but is far from being airtight. By patching holes in the foundation we--thank heavens!--got rid of a family of Striped Skunks that temporarily took up residence a few years ago, but there's no way we can--or really want to--eliminate all the interesting little critters that come and go. When bugs and beetles show up in the kitchen we don't use a fly swatter or boot heel, preferring to catch these insects in a drinking glass and free them outside. We've had bats in our belfry--or at least clustered on louvered vents in our eaves--and several generations of Black Rat Snakes have glided up a Flowering Dogwood tree outside our office window before entering the attic in pursuit of whatever tasty prey they might consume. Occasionally a near-fledgling Chimney Swift appears in the living room fireplace (with adult, above right)--requiring we act as surrogate parents for a few days--and several times each year we have to round up a fast-moving Carolina Anole (male, below left) from an interior windowsill to return it to the wild. We do treat for termites as our mortgage requires and occasionally spray to ward off carpenter ants, but we have no Oriental Cockroaches thanks to the efficient work of solitary Wolf Spiders that patrol the premises with our blessings. We count all this as part of "the joy of country living" but lest you think Hilton Pond Center is overcome by vermin, on most days we encounter NONE of these animals--just like you seldom see all the organisms that undoubtedly pass through or live in your OWN home. That said, among our most common household visitors--especially when crisp days of autumn arrive--are sundry so-called "field mice" that invite themselves in from the cold.

When we walk the Center's trails by night or fill our bird feeders after sunset we sometimes hear something rustling about in dead leaves on the ground. With a flashlight we often pick up eyeshine--usually from a larger animal such as a grazing Eastern Cottontail or a masked Raccoon (at right), ambling in to glean seeds from beneath the feeders. More often our beam reveals a pair of beady little inch-apart eyes that stare right back at us--eyes of those very same "field mice" that grace the halls and closets of the Center's old farmhouse come winter. Actually, this term "field mouse" is widely used but isn't very useful because there are lots of different kinds of little mice that inhabit fields and meadows. Based on experience, we'd be more accurate in saying what we're looking at in the darkness is one of the Peromyscus mice--but which one?

All text & photos © Hilton Pond Center

Peromyscus is likely the largest mammalian genus in North America with roughly 55 species and numerous subspecies. Every U.S. state (except Hawaii) has at least one kind of native Peromyscus, as is the case with the Mexican states, most Canadian provinces, and Central America as far south as western Panama. (We regret the need to mention several Peromyscus species are recently extinct, having lost their specialized habitats to human activities.) The Carolinas are home to four species of Peromyscus, some with overlapping ranges and similar morphologies that can make accurate identification rather difficult--even with the mouse in-hand or viewed up-close through a macro lens (above).

The Oldfield Mouse, P. polionotus, is found in the western half of South Carolina and barely gets into North Carolina in southern Rutherford County; it is more common in the South Carolina Sandhills where it can dig burrows easily in sandy old fields--hence its common name. This is the most easily identified of the four Carolina Peromyscus, being paler in pelage and smaller in body size and length of hind foot (14-18mm). Hilton Pond is within the geographic range for Oldfield Mouse but we haven't documented it locally to date. Much less likely to occur here is the Cotton Mouse, P. gossypinus, whose populations are densest in the Coastal Plain and Sandhills of the Carolinas. It is essentially absent from the northwestern corner of South Carolina and to our knowledge has not been reported from here in York County. Cotton Mice have darker fur and big hind feet (22-25mm) and are more likely found in riparian habitats such as swamps and flood plains. They take their common name from their habit of including tufts of cotton in their nests.

All text & photos © Hilton Pond Center

The other two Peromyscus species of the Carolinas are the ones most likely to be confused with each other, especially in more northerly parts of their range; these are the Deer Mouse (P. maniculatus) and the White-footed Mouse (P. leucopus, above). Despite their names, BOTH species have white hind feet, but because of size overlap foot length cannot be used to separate the species. Tail measure is also of little use because of overlap, although in White-footed Mice this appendage is generally shorter.

All text & photos © Hilton Pond Center

Thus, to separate P. maniculatus from P. leucopus one should look at a combination of attributes: 1) tail coloration (heavily bi-colored in the Deer Mouse with the dorsal surface much darker than the ventral, while the tail is indistinctly two-toned in White-footed Mouse as shown above); 2) tail fur (Deer Mouse generally has more hair on its tail and a large tuft at the tip); 3) ear (larger, more hairy in White-footed Mouse, with an edge of whitish fur as in photo just below); and, 4) flank (the delineation between dark dorsal fur and white belly fur is generally more distinct in White-footed).

All text & photos © Hilton Pond Center

Of even greater usefulness in identifying these two mice with similar appearances are their respective distributions. We're confident we have no Deer Mice at Hilton Pond Center because the species occurs only in woodlands of the Mountain Provinces of the Carolinas, where they might be the most plentiful of all small mammals. By comparison, White-footed Mice in South Carolina occur mostly above the fall line--including the Center--where they inhabit a diverse set of habitats such as hardwood forest, fence rows, and grassy edges. Prolific populations of White-footed Mice are an important part of the natural food chain, serving both as seed dispersers and as abundant prey for everything from weasels to foxes and hawks to crows.

All text & photos © Hilton Pond Center

Without a doubt all these little indoor rodents at Hilton Pond Center are White-footed Mice that have expanded their habitat to include human dwellings in the Carolina Piedmont. On any given day autumn through spring there's likely to be an outdoor mouse inside our house, but they do little damage and since they're primarily nocturnal we seldom know they're here. Occasionally they leave their little calling cards--quarter-inch elongated black droppings (right) that are the end result of their having chewed into a package of saltine crackers in the pantry. Usually, however, we're alerted to their presence only by the metallic sound of the door snapping shut on a Sherman live trap (below).

All text & photos © Hilton Pond Center

We much prefer these portable aluminum devices to old-style mouse traps that--traditionally baited with cheese--snuff out the life of the mouse by breaking its neck. Better to catch our White-footed Mice alive and transport them to the woods where they can hang out in a more natural place of residence--or maybe end up as a midnight snack for the family of a Great Horned Owl.

All text & photos © Hilton Pond Center

POSTSCRIPT #1: When we first came to Hilton Pond in 1982 we occasionally encountered a House Mouse (Mus musculus) in the farmhouse, but it's been at least 25 years since we've seen one of these invasive rodents whose ancestors undoubtedly were introduced by the first European visitors to North America. We also no longer encounter the much larger and even more destructive Norway Rat (Rattus norvegicus). Perhaps these two non-natives were better adapted to agricultural habitat that made up Center property three decades ago and today just don't compete with White-footed Mice and Hispid Cotton Rats (Sigmodon hispidus) that are native species more at home in meadows and woodland that now predominate.

POSTSCRIPT #2: Despite our admiration for and appreciation of Peromyscus mice with which we share Hilton Pond Center's old farmhouse, we're well aware in some situations these beady-eyed little rodents might pose a health risk by serving as vectors of hantavirus and Lyme disease. That said, hantavirus is usually contracted by people when they inhale dust from old mouse nests or droppings in particularly dirty locations, while Lyme disease is acquired from the bite of a tick that previously fed on blood of an infected mouse. As a precaution we're quite careful concerning what we inhale and about keeping ticks off our skin.

All text & photos © Hilton Pond Center

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