Small Mammal Survey

We performed a small mammal survey for a Maryland client.  We installed twelve 100-foot line (index) transects, using aluminum collapsible Sherman Live Traps, placed every 20-feet along the transect, for a total of six traps per line.  The sixth trap at the 100-foot mark of each transect was an in-ground, PVC plastic pitfall trap.  A total of 72-traps were monitored.


All of the field work was performed in May of 2012.  The traps were installed, pre-baited and locked in the open position for a five-day period.  Eight-days of live trapping was then performed.  The transect locations occurred in old-field meadows, within woodlands and along littoral fringes of marshlands.

Six species of small mammals were caught, measured, documented and photographed, including deer mouse (20), white-footed mouse (18), house mouse (14), meadow vole (14), marsh rice rat (5), and least shrew (3).  Chipmunk and gray squirrel were also observed but not caught.  A total of 76 animals were captured and documented through the eight-days of live-trapping, including 1 mature green frog and 1 juvenile box turtle.

All of the captured/observed species are considered relatively common, and all of the species except for the house mouse are native and endemic to the western shore, northern coastal plain (Major Land Resource Area 149A) of Maryland.  The stated purpose of the study was to determine if any rare, threatened and/or endangered (RTE) small mammal species occur at our site.

The following is an overview of the species collected and documented:

The deer mouse (Peromyscus maniculatus) below, is brownish on the head and sides, with a slightly darker stripe that extends down the middle of the back; the underside and feet are white.  The long tail is distinctively bi-colored, dark brown above and white below, and the small tuft of hairs conceals its tip.  The large scantly-haired ears are dusky in color, their margins edged with distinctly paler hairs.


Deer Mouse Critical Diagnostics:  Noticeable tuft of fur on the tip of the tail, distinctly bi-colored and well haired.  Tuft of white hairs on tip. Total 152 to 200 mm.  Tail 72 to 102 mm.  Foot 18 to 23 mm.

Deer Mouse Habitat Preference:  Deer mice utilize mixed evergreen and cool, damp deciduous forests, but can also be found in grasslands, meadows and agricultural fields.


The head and sides of the white-footed mouse (Peromyscus leucopus) below, are brownish, the mid-dorsal stripe is slightly darker and the belly and feet are white; the line separating the brown sides and white belly are distinct.  The tail is indistinctly bi-colored, being brownish above and whitish below.  The large dusky-colored ears are narrowly edged with white.


White-Footed Mouse Critical Diagnostics:  White feet including ankles.  Tail not distinctly bi-colored and shorter than combined head/body length.  Total 152 to 188 mm.  Tail 65 to 92 mm.  Foot 17 to 22 mm.

White-Footed Mouse Habitat Preference:  Hardwood forests are the choice habitat, but field margins, marshes and brushy fence/hedgerows are also inhabited.  This mouse seldom occurs in grass fields.


The house mouse (Mus musculus) below, has an elongated snout; small, slightly protruding black eyes; large, naked ears; and a scaly tail that is scantly haired.  Color varies from grayish brown to brown above, grading to gray. buff or white on the belly, feet and undersides of the tail.


House Mouse Critical Diagnostics:  Elongated snout, small black eyes, large ears, scaly tail that is scantly haired.  Total 140 to 180 mm.  Tail 58 to 93 mm.

House Mouse Habitat Preference:  The non-native house mouse is found commonly in close association with humans – in houses, restaurants, factories, warehouses, barns and other man-made structures.  It also lives abundantly in the wild, in weedy and overgrown abandon fields, hedgerows and grain fields.


Meadow voles (Microtus pennsylvanicus) below, are small rodents characterized by short tails and ear openings that are partly guarded by fur.  They have short, dense fur and relatively short ears, but the tail, also short, is more than twice as long as the hind foot, and is longer than other species of voles.  Color on the back and sides varies from chestnut-brown in the summer and dark gray-brown in thew winter, and the belly fur is dark gray.


Meadow Vole Critical Diagnostics:  Long tail for a vole, but still very short.  The tail is bi-colored, and is the most common vole species, robust and bigger than most all mouse species.  Eats tree bark/seedlings.  Total 139 to 190 mm.  Tail 39 to 54 mm.

Meadow Vole Habitat Preference:  The meadow vole prefers damp meadows, brackish marshes, grassy upland fields and woodlands with a dense layer of herbaceous plants covering the ground.


The marsh rice rat (Oryzomys palustris) below, is a medium-sized rodent that resembles the Norway rat but is much smaller and has a tail that is sparsely furred.  The tail of the marsh rice rat is about as long as the head and body, and the feet are whitish.  This rat usually has grayish brown upper-parts and is paler below.  The fur is relatively short and smooth.


Marsh Rice Rat Critical Diagnostics:  Larger overall size, long scaly tail sparsely furred, darker on the top, lighter on the bottom, short furry ears.  Total 180 to 290 mm.  Tail 90 to 140 mm.  Foot 29 mm.

Marsh Rice Rat Habitat Preference:  As the common name suggests, these rats are animals of marshes and marsh edges.  They occupy fresh and brackish wetlands and will venture into upland grasslands adjacent to marshes.


The least shrew (Cryptotis parva) below, has a long nose, very small eyes, inconspicuous ears, and a short tail.  The fur is brownish gray above and paler below, with a silver frosting on each hair.  The least shrew can be separated easily from other members of the genus by the length of its tail, which is much less than half the head and body length.


Least Shrew Critical Diagnostics:  The largest of our endemic shrews.  Very short tail, and a somewhat cinnamon color coat with silver tip frosting on each fur ends.  Total 70 to 92 mm.  Tail 13 to 26 mm.  Foot 8 to 15 mm.

Least Shrew Habitat Preference:  A wide variety of habitats are frequented by least shrews, but relatively open areas dominated by herbaceous vegetation, such as grassy fields and marshes are preferred.


When we saw that a trap door was closed, we picked it up and feel if it was weighted.  If so, we know we caught a critter.  With gloves on, we then dropped the animal into a plastic bag and then reached in to hold the animal for measurements, identification and photos.  We sure did not expect to capture a mature green frog, as our bait was a combination of peanut butter and various seeds.


This juvenile box turtle was a surprise to capture.


The only issue that we thought could be problematic, would be if a peanut butter addicted raccoon, opossum or squirrel got wind of our transect lines and vandalized our traps each evening in the hopes to opportunistically feed on grains and peanut butter.  We did have some door tripping, primarily due to squirrel in our woodland transects, and we did have one trap that got beat-up pretty bad as a frustrated raccoon clawed and bent the trap.  We also had a few traps carried off several feet from the transect lines, and we only lost one trap, as an animal took it far away.  At some of our locations we installed motion detection cameras, where we got photos of squirrel, raccoon, ground hog and barred owl.

We were able to create a great spreadsheet of diagnostic keys to small mammal species of Central Maryland.  Our primary tools included a small metric ruler and metric calipers.  We only lost one mouse and one shrew, that died most likely from overheating during the day in the closed traps.  Otherwise all of the critters were re-released away from our transects.  What a fun job!