NORTHERN BAJA DEERMOUSE Peromyscus fraterculus 169–218mm, 92–117mm, 18–40g
Like Cactus Deermouse but lives in Southern California and Baja Peninsula. Recently described as a unique species based on genetic data, no morphological or ecological differences between the Cactus and Northern Baja Deermouse are known(see yellow area on Cactus Deermouse map).
MERRIAM’S DEERMOUSE Peromyscus merriami 185–225mm, 95–120mm, 20–30g
Small to medium-sized mouse, somewhat darker above than the Cactus Deermouse, with creamy underparts. Usually larger than the Cactus Deermouse, darker on the back, with a creamy (not white) venter. Has a less densely haired tail than the Canyon Deermouse without a tufted tip. Occurs in bosques – dense thickets of mesquite, often mixed with cholla, prickly pear, palo verde, vines, and grasses.
BLACK-EARED DEERMOUSE Peromyscus melanotis 140–170mm, 50–73mm 17–28g
Like the North American Deermouse (plate 52) but occurs in southeastern Arizona and New Mexico. Differs from most other Peromyscus by being smaller, with a shorter tail and in having black preauricular hairs at anterior base of ear. This species was recently described from genetic data, and can only be distinguished from the North American Deermouse by having a slightly smaller black tuft, a broader and more rounded braincase, and a longer and more slender rostrum.
PLATE 55
PEROMYSCUS TRUEI AND BOYLII GROUPS
PION DEERMOUSE Peromyscus truei 171–231mm, 76–123mm, 15–50g
Medium-sized mouse with large ears and a hairy tail. Ears are longer than the hind feet, and relatively larger than other Peromyscus. The tail has a dark dorsal stripe and is tipped with long hairs. Favors rocky slopes with pinyon pine and juniper.
NORTHERN ROCK DEERMOUSE Peromyscus nasutus 194–198mm, 98–102mm, 24–32g
Fairly large, gray-brown mouse with a long, hairy, bicolored tail and large ears. The underparts are paler. Quite similar to P. boylii, but with slightly larger ears (17–28mm). Smaller than P. gratus with slightly longer feet (22–28mm) and ears. The tail sheath is much more likely to break in P. nasutus than in P. boylii. Tail has more fur than most other Peromyscus. Uses boulder-strewn regions in pinyon-juniper and oak woodland zones.
SAXICOLINE DEERMOUSE Peromyscus gratus 171–231mm, 76–124mm, 19–33g
Has a brownish to brownish-black back and a long tuft of hairs on the tail tip. The underparts and hind feet are whitish. The tail is longer than the head and body, brownish on top, whitish underneath, and covered with short hairs except for long hairs on tip. Fur is darker in populations living on lava flows. Slightly larger than Northern Rock Deermouse, with a slightly longer tail, and slightly shorter hind feet (20–26mm) and ears (17–23mm). Uses a variety of rocky areas.
TEXAS DEERMOUSE Peromyscus attwateri 187–218mm, 96–112mm, 25–35g
Medium-sized Peromyscus with large hind feet and ankles that are usually dark or dusky, and ears that are medium-sized compared to other Peromyscus. The tail is bicolored, well tufted, and equal in length to head and body. Uses cedar glade, juniper-grass, and oak-juniper forests.
BRUSH DEERMOUSE Peromyscus boylii 175–210mm, 89–115mm, 22–36g
Has unique broad, bright orange lateral line extending from the cheek to the hindquarters. The back is medium brown and the sides paler brown, grading to white or cream on underparts. Ankles are dusky gray. Ears and hind feet are similar in size. Tail is bicolored, longer than the head and body, well haired, and tufted at end. Has smaller ears (16–20mm) than the Northern Rock Deermouse. Uses rock outcroppings and brushy or forested areas in elevations more than 2000m. Rock ledges, boulders, brush piles, and fallen trees are typical of its habitat.
WHITE-ANKLED DEERMOUSE Peromyscus pectoralis 185–219mm, 92–117mm, 24–39g
Medium in size, with ears shorter than the hind feet, ankles that are usually white, and a tail that is hairy and coarsely ringed. Similar to Texas Deermouse, but slightly paler, with a more distinctly bicolored tail and smaller hind feet (less than 24mm). Uses rocky situations in arid mountain regions and in Texas Hill Country.
PLATE 56
SIGMODON
COTTON RATS-SIGMODON SPP. - Vaguely volelike in general appearance but larger, cotton rats also make runways in grassy areas. These medium-sized rats have stocky bodies with somewhat harsh fur. The three central digits on the hind foot are larger than the other two. The generic name refers to the S-shaped pattern of the cusps of the cheek teeth.
HISPID COTTON RAT Sigmodon hispidus 224–365mm, 81–166mm, 110–225g
Pelage is grizzled with blackish or dark brownish hairs interspersed with buff or grayish hairs. Sides are only slightly paler and underparts are pale to dark grayish, sometimes faintly washed with buff. No orange eye or nose ring. Juveniles are covered with short, darker pelage by one week of age. Smaller than the Arizona Cotton Rat, with smaller feet (32–34mm). Tail short, scaly, and sparsely haired. Uses habitats with grasses especially little bluestem and bushy beardgrass.
YELLOW-NOSED COTTON RAT Sigmodon ochrognathus 132–264mm, 80–114mm, 51–106g
Small cotton rat with a yellowish patch on each side of the nose. Back is muddy gray and underparts are silvery or whitish. Color of the inside of the pinna of the ear the same as the dorsum. Dorsal guard hairs and underhairs are grayish with a tinge of yellow, whereas those of the venter are grayish white. Small hind feet (less than 30mm) are buff-gray, and tail is hairy and blackish above, grayish below. Uses grassy patches in montane situations, especially dry rocky slopes.
ARIZONA COTTON RAT Sigmodon arizonae 200–349mm, 85–156mm, 125–211g
Look like grizzled rats with scaly tails. They are similar to, but slightly larger than Hispid Cotton Rats with a hind foot larger than 34mm. Local populations sometimes increase rapidly after summer rains. Breeding begins in earnest then, although they probably breed year-round except in the driest conditions. Females produce a litter of 2–10 precocial young after a gestation period of about 27 days and weaning occurs after 15–25 days. Common in grassy areas around ponds, drainages, riparian areas, irrigated fields, and weedy or brushy areas.
TAWNY-BELLIED COTTON RAT Sigmodon fulviventer 223–270mm, 94–109mm, 200–222g
The largest Sigmodon has a back that is pepper and salt in color and underparts that are washed with buff. Tail is dark and usually covered with just enough hairs to hide the scales, which are smaller than those of the Hispid Cotton Rat. Builds grass nests connected to feeding areas by runways through the grass. Litter size is 4–6 after a gestation period of 35 days. Young leave the nests after just a week, and are capable of breeding at about 6 weeks of age. Uses grass and grass-shrub habitats.
PLATE 57
ARBORIMUS VOLES
ARBORIMUS VOLES - These small, reddish voles almost never descend to the ground from their arboreal homes. Therefore, they are rarely seen and poorly known. Long thought to be a subgenus of heather voles, these tree voles differ in having longer tails, smaller ears, longer feet, and wider and shorter teeth.
RED TREE VOLE Arborimus longicaudus 158–206mm, 60–94mm, 25–47g
Slightly larger than White-footed Vole, with pelage that is thick, long, and soft. Back is red and lacks a medial stripe. Animals from the northern Oregon coast are larger, with brownish-red backs and pale gray undersides; southern and inland animals are brighter colored with undersides washed in reddish orange. Tail is long, hairy, and black to brown. Eyes are small and ears are pale and hairless. Distinguished from Sonoma Tree Vole by not being as brightly colored and by having nasal bones that extend beyond the maxillaries. Home ranges are small, sometimes restricted to a single tree. Their preference for old-growth forest has resulted in population declines as the forests are logged. Secretive and nocturnal, they spend most of the time in the tops of tall conifers, eating needles of Douglas fir.
SONOMA TREE VOLE Arborimus pomo 158–187mm, 60–83mm, 25–47g
Like the other Arborimus, but with reddish fur that is gray at the base. Many hairs are tipped sligh
tly with black. Belly is white (with gray base to hairs) and often washed with reddish orange. Skin on tail is black and covered with reddish fur. Tail is well haired, thick, and more than half the head and body length. Ears are almost hairless. More brightly colored than Red Tree Vole, with nasal bones that do not extend beyond the maxillaries. Nests are hard to spot, as they are very high (10–30m) in trees, most commonly Douglas fir, grand fir, and sitka spruce. Males may be more terrestrial than females, as their nests are occasionally found on the ground. They feed almost exclusively on fir needles and bark, which they collect daily and store on top of the nest. They feed in the nest during the day, and forage for fresh needles at night. Solitary, but more than one nest may be found in a single tree. Very arboreal in coniferous trees at the forest edge adjacent to meadows, fields, and canyons.
WHITE-FOOTED VOLE Arborimus albipes 149–182mm, 57–75mm, 17–29g
Small wooly mouse with white feet and fur that is long, soft, and a warm brown color. Belly is gray and sometimes washed with pale brown. Long, thinly-haired tail is black on top and white below. Feet are usually white on top, and ears, which are usually hidden by the fur, are hairless. They are herbivorous, feeding on both herbaceous material and roots. Litters of 2–4 young are produced year-round. Nocturnal, they may also be capable of burrowing as they are the most terrestrial of the Arborimus, found in riparian alder habitats along small streams.
PLATE 58
RED-BACKED VOLES
RED-BACKED VOLES-MYODES SPP.-Aptly named, with a chestnut-brown to reddish-brown stripe on the back that grades to dark gray or buff-gray on the sides and belly. Pelage is long and soft in winter and short and coarse in summer. This genus was historically known as Clethrionomys.
WESTERN RED-BACKED VOLE Myodes californicus 121–165mm, 34–56mm, 15–40g
A brownish vole with a faint red stripe down center of back. Tail is long and indistinctly bicolored, dusky above and whitish below. The subspecies C. c. californicus from the coast is darker with its red stripe largely obscured by black hair. Inland animals are typically paler. Dorsal stripe not as obvious as in the Southern Red-backed Vole. Tail is longer and more bicolored than in the Northern Red-backed Vole. Underground nests are built in burrows, under logs, or deep in the litter. Mostly nocturnal, but may be active throughout the day in some areas. They feed mainly on fungus and lichens, but some conifer seeds and insects are also eaten. Favors very old (200-year) stands of western coniferous forests with little undergrowth. Forages mostly under surface of the forest floor.
SOUTHERN RED-BACKED VOLE Myodes gapperi 116–172mm, 30–50mm, 6–42g
Brilliantly colored, can easily be distinguished by broad, reddish band running from forehead to rump. Nose, sides of head, and body are gray, often with a yellowish cast. Belly colors range from silvery white to pale yellowish, and the tail is bicolored. There are two distinct color phases in northern and eastern subspecies with either bright reddish or more grayish-brown dorsal bands. This dorsal stripe is brighter and more distinct than in other Myodes species. Feet are pale drab gray. Active year-round, mostly at night and dusk. Breeding season is March-November. Uses natural runways along and beneath logs, rocks, and roots of trees. Found in mesic coniferous, deciduous, and mixed forests with abundant litter of stumps, rotting logs, and exposed roots.
NORTHERN RED-BACKED VOLE Myodes rutilus 127–161mm, 30–48mm, 23–40g
This species is very similar to the Southern Red-backed Vole, but has a duller red back with slightly more red hairs on the sides. The tail is relatively thick and short. Active year-round but breeding season is April–September, somewhat shorter in the northern part of the range. Litter size is 6–8, young develop rapidly, and those born early in the year may breed in the year of their birth. Feeds on seeds, berries, mushrooms, lichens, leaves, and some insects. Although population size varies widely, they do not show regular cycles. Replaces House Mouse as inhabitant of buildings in the far north. Occurs in both taiga and tundra habitats, all essentially north of the range of the Southern Red-backed Vole.
PLATE 59
COASTAL MICROTUS
MICROTUS VOLES - The most common and diverse of the voles, typically live in grasslands where they form runways between their nests and feeding areas. Voles are stout-bodied mice with long, loose pelage and short tails. The ears are so short and rounded as to be almost concealed by the pelage.
GRAY-TAILED VOLE Microtus canicaudus 140–168mm, 32–45mm, 35–55g
Small but robust vole with large eyes. Yellowish-gray or brown above, venter is grayish white. Feet are gray, and short tail is gray with a brownish dorsal stripe. Has shorter tail and paler fur than Townsend’s Vole; has larger eyes and is more robust than Creeping Vole. Breeding occurs from March to November and litters of 4 or 5 young are born after a gestation period of 21 days. Development is rapid, and females are capable of breeding at 18 days of age, shortly after weaning. Uses low-elevation grasslands, including agriculture planted in small grains or legumes.
CALIFORNIA VOLE Microtus californicus 139–207mm, 38–68mm, 30–81g
Medium-sized vole with tail of moderate length and belly fur that is pale with gray at the base. Grizzled brownish with scattered black hairs above. Long tail is bicolored. Feet are pale. Occurs at lower elevations than Montane Vole; has shorter and less bicolored tail than Long-tailed Vole; larger than Creeping Vole, and has six plantar tubercles; slightly larger than Townsend’s Vole. The subspecies near Inyo County, California(M. c. scirpensis), is Endangered. Prefers low-elevation grasslands and wet meadows, but also found in coastal wetlands and open oak savannas with good ground cover.
CREEPING VOLE Microtus oregoni 130–153mm, 30–41mm, 17–20g
Small vole with short, dense dorsal fur that is sooty gray to dark brown or almost black with a mixture of yellowish hairs. Belly is a dusky gray to white. Eyes are especially small, tail is short, almost black on top and gray underneath. Small size and tiny eyes distinguish it from other voles. Has five plantar tubercles on feet. They feed on herbs and grasses in addition to fungi. Most of their time is spent underground, and nests are in burrows or under tree roots or rotting logs. Occupies grassy and herbaceous sites within moist coniferous forests, including recent clearcuts.
TOWNSEND’S VOLE Microtus townsendii 169–225mm, 48–70mm, 47–83g
One of the largest voles, with dark brownish fur and large ears. Tail is long, and blackish or brownish. Feet are brownish or blackish with brown claws and six plantar tubercles. Ears are large and broad and extend above the fur. Large size distinguishes it from other voles. They are good swimmers, capable of crossing small streams. Nests are on or above the ground, often in slightly higher areas, to avoid flooding. Found in wet meadows and marshes with dense grass and sedge cover, from sea level to 1800m.
PLATE 60
OTHER WESTERN VOLES
MONTANE VOLE Microtus montanus 140–220mm, 24–64mm, 18–90g
Small vole, grizzled brown to blackish above, often with buff tint. Belly fur is white to gray, not buffy like Prairie Vole. Moderately long, bicolored tail, but shorter than that of Long-tailed Vole. Feet are dusky or silver gray, darker than in the White-footed Vole, but lighter than in the Meadow Vole. Back hairs are paler than those of Meadow Vole, although the best way to distinguish these two is to count the elements on the upper second molar, which has 4 elements in the Montane Vole but 5 in the Meadow Vole. Experienced field workers can evaluate this trait with live animals by obtaining a dental impression on wax; amateurs should take care to avoid getting vole tooth impression on their fingers. Adult males often have oily skin glands on hips in breeding season, unlike most other voles. Found in dense woods, wet meadows, and stream sides and, especially, mesic grasslands.
LONG-TAILED VOLE Microtus longicaudus 155–202mm, 49–81mm, 36–59g
Small, thick-bodied, grayish vole with long bicolored tail. Feet have six plantar tubercles. Ears are large and haired, and eyes are large. Color of back from ashy gray to brownish gray. Numer
ous black-tipped hairs occur on the back, but the sides are more grayish. Color and long tail distinguish it from other voles. The breeding season is May–October, and females produce litters of about 5 young. The diet includes fruits, seeds, fungi, bark, and leaves. Occurs in mountain-top habitats with coniferous and hardwood forests, brushy thickets, forest meadow ecotones, and riparian areas.
NORTH AMERICAN WATER VOLE Microtus richardsoni 234–274mm, 66–98mm, 72–150g
North America’s largest vole. Has long pelage that is grayish brown or dark reddish brown on the back, often darkened with black-tipped hairs. Underparts are grayish with a white or silvery-white wash. Bicolored tail is dusky above and grayish below. Has five plantar tubercles on the feet. Large hind feet (more than 23mm) distinguish it from other voles. Active throughout the day, but more so at night. Semiaquatic, and uses subalpine and alpine meadows close to water, especially swift, clear spring-fed or glacial streams with gravel bottoms, and along the edges of high-elevation ponds between 1500 and 2300m.
Mammals of North America Page 11
