DESERT WOODRAT Neotoma lepida 245-352mm, 101-162mm, 85-186g
Feet are white, ears are large, and throat hairs are dark. Smallish woodrat, pale gray-brown dorsally, with a distinctly bicolored tail. Larger and darker than the Arizona Woodrat. Smaller than Bryant’S Woodrat, with finer hairs, and paler coloration. Builds sloppy stick nests around cacti, or on rocky crevices. Found in desert scrub in many of the drier deserts of North America (see red area on map).
BRYANT’S WOODRAT Neotoma bryanti 284-387mm, 132-179mm, 105-209g
A large rat like the Desert Woodrat but darker. Pelage is relatively stiff and coarse. Its bicolored tail is black above, not brown, and relatively longer than the Desert Woodrat. This woodrat prefers coastal sage scrub, and also occurs on many islands of the Baja peninsula (see yellow area on map of Desert Woodrat).
ROOF RAT Rattus rattus 325-455mm, 160-255mm, 115-350g
Scaly, sparsely haired, uniformly dark tail that is longer than the head and body. This dark rat has a brownish-gray back and a grayish belly (not white like woodrats). Introduced from Europe with earliest colonists. Widespread in south and coastal areas. Frequents urban areas, buildings, and warehouses.
BROWN RAT Rattus norvegicus 315-460mm, 120-215mm, 195-485g
Similar to Roof Rat, but with tail shorter than head and body. Scaly tail and dark belly distinguish it from woodrats. A later introduction that has outcompeted Roof Rats in many areas. Widespread from southern Canada throughout United States in both urban and old field habitats.
PLATE 49
GRASSHOPPER MICE AND ORYZOMYS
GRASSHOPPER MICE - ONYCHOMYS - These are among the most predaceous rodents, feeding mainly on insects and scorpions at night. They are characterized by a relatively short tail, and have a loud, pure tone vocalization that is audible to humans. The three species are nearly identical, and best distinguished by geographic range.
NORTHERN GRASSHOPPER MOUSE Onychomys leucogaster 120-190mm, 30-60mm, 25-50g
Large grasshopper mouse with relatively short tail. Back may be grayish or cinnamon-buff; underside is white. Tail tip may be white. Found in arid and semiarid habitats throughout western North American shrub steppes and grasslands.
SOUTHERN GRASSHOPPER MOUSE Onychomys torridus 130-160mm, 40-60mm, 20-40g
Differs from Chihuahuan Grasshopper Mouse only in genetic details, but ranges do not overlap. Compared with the Northern Grasshopper Mouse, is smaller with a relatively long tail. Grayish or pinkish-cinnamon above; white below. Occurs in arid habitats throughout Sonoran and Mojave deserts, plus chaparral in California (yellow area on map).
CHIHUAHUAN GRASSHOPPER MOUSE Onychomys arenicola 120-160mm, 35-55mm, 20-35g
Differs from Southern Grasshopper Mouse only in genetic details, but ranges do not overlap. Smaller than the Northern Grasshopper Mouse, with a relatively larger tail. Occurs in low desert-scrub habitats in Chihuahuan Desert, and extending slightly northward (see red area on map of Southern Grasshopper Mouse).
ORYZOMYS - Previously known as rice rats, this genus of nocturnal, mostly aquatic rats is diverse in the neotropics (more than 36 species), but only two species reach the United States. Semiaquatic feeders on seeds, vegetation, and occasionally invertebrates. They are mouselike in appearance, with coarse pelage that is neither bristly nor spiny. They have long tails with visible rings under sparse hair.
COUES’S ORYZOMYS Oryzomys couesi 390-410mm, 130-140mm, 65-70g
Large brown Oryzomys with long tail. Back is dark brown, sides are pale brown, and belly is even paler. Builds nests of leaves, twigs, and vines in cattails or small trees over the water. Uses a variety of marshy habitats.
MARSH ORYZOMYS Oryzomys palustris 195-260mm, 95-120mm, 45-80g; 190-255mm, 85-115mm, 40-60g
Small grayish Oryzomys with tail about equal to head and body length. Has a dark mid-dorsal stripe, the belly and feet are whitish, and the tail is bicolored. Active all year. Makes grapefruit-sized nest of grasses. Some consider the silvery-gray subspecies O. p. argentatus of Florida Keys to be full species. The subspecies O. p. natator in the lower Florida Keys is Endangered. Found in marshy areas of Atlantic coast and southern United States.
PLATE 50
CENTRAL AND EASTERN TINY MICE
NORTHERN PYGMY MOUSE Baiomys taylori 87-123mm, 34-53mm, 6-10g
North America’S smallest rodent. Varies from reddish brown through gray to almost black above, and white to creamy buff or gray below. Tail is covered with short hairs, and may be uniformly gray or paler ventrally. Incisors are ungrooved. Uses a variety of habitats including prairie, mixed-desert shrub, post oak savanna, and pine oak forests.
HARVEST MICE - Mice in this genus are distinguished by their small size and the single groove on each upper incisor.
FULVOUS HARVEST MOUSE Reithrodontomys fulvescens 134-189mm, 73-116mm, 6-25g
Small fulvous mouse. Upperparts vary from reddish-yellow buff to tawny to pinkish cinnamon or salmon. The pelage is mixed medially with blackish hairs that sometimes form a darker band down the midline from nose to tail. Underparts vary from white to gray, often tinged with buff or pale pinkish cinnamon. Tail is brown to dark brown above and only indistinctly bicolored. Feet are grayish white to buff-white and ears are varying shades of brown, often with a tawny or reddish-yellow tinge on the inner surface. The pelage is coarser than in other harvest mice, with a streaked salt-and-pepper effect from the black guard hairs. Larger and brighter than Eastern Harvest Mouse. Less gray than Plains Harvest Mouse with a relatively shorter tail that is not bicolored. Often trapped near rocky outcrops and cacti. Constructs baseball-size nests of grasses and sedges in vegetation off the ground. Uses grassy fields with shrubs, especially mesquite grassland, grassland, pine-grass ecotones, and grass-brush habitats.
EASTERN HARVEST MOUSE Reithrodontomys humulis 107-128mm, 45-60mm, 10-15g
Small, brown mouse with a relatively short tail. Upper parts are rich brown, sometimes faintly washed with gray, and with a dark mid-dorsal stripe. Sides are paler than the dorsum, with an obvious lateral line present. Underparts are ash-colored and often have a cinnamon or pinkish wash. Tail is slender, sparsely furred, bicolored, and shorter than the head and body. Ears are fuscous or fuscous-black in color, and feet are grayish white. Similar to R. fulvescens, but tail is shorter and more bicolored. Uses broom sedge, grassy or weedy areas, tangled patches of briar, roadside ditches, brackish meadows, and wet bottomlands.
PLAINS HARVEST MOUSE Reithrodontomys montanus 54-146mm, 20-69mm, 6-13g
Small, grayish mouse with a diffuse dark stripe down the middle of its back and a short bicolored tail. Remainder of fur on back is grayish brown and the underside is white. Tail is shorter than head and body, bicolored, with a sharp dark line above and paler color below. Tail is sparsely haired, but does not appear scaly. There is a bright tuft in front of the ears and a spot behind them. Similar to Eastern Harvest Mouse, but larger and paler, with paler ears. Uses grassy areas in the Great Plains.
PLATE 51
HOUSE AND WESTERN TINY MICE
WESTERN HMARVEST MOUSE Reithrodontomys megalotis 118–170mm, 50–96mm, 8–15g
Small mouse with a relatively long, bicolored tail. Fur is bristly and relatively short. Feet are whitish. The ears are comparatively small and buff to reddish brown. The tail is about as long as the head and body and distinctly bicolored, with relatively long hairs that tend to obscure the scales. Juveniles are grayish brown; subadults are brighter than juveniles but duller than adults. The thick winter pelage is paler and the tail is more distinctly bicolored. Some animals east of the Mississippi River and in the San Francisco Bay area have a buff pectoral spot. Larger than Plains Harvest Mouse, with longer hair and a more distinctly bicolored tail. Larger than Eastern Harvest Mouse, with a relatively longer tail. Has a less pointed, more bicolored tail than Salt-marsh Harvest Mouse. Makes spherical nest of grasses and other plant fibers, lined with softer material, with an opening near the bottom. These are often on the ground, but may be up in the shrubs,
or sometimes even underground in the burrows of other animals. Feeds on herbs, seeds, and insects, including ground beetles when available. They can climb in the shrubbery to reach flowers and seeds. Although they do not make food caches, they do lay down body fat in the fall. They do not hibernate, but can become torpid for short periods, relying on fat stores to get them through periods of extreme weather. This species is very widespread and tolerant of a wide range of habitats, ranging from arid deserts and sand dunes through fallow fields, woodland clearings, and disturbed habitats such as roadsides and fence rows from sea level to 4000m.
SALT-MARSH HARVEST MOUSE Reithrodontomys raviventris 118–175mm, 56–95mm, 7–15g
A small reddish mouse from the San Francisco Bay area. The subspecies from the south end of the bay(R. r. raviventris) has dark, cinnamon-colored back with a tawny lateral line and a pale to cinnamon belly. Mice from the north end of the bay(R. r. halicoetes) have paler upperparts with no lateral line and a white belly. Similar to Western Harvest Mouse, but with a more unicolored tail. They may have 2 or 3 litters per year, but populations are small due to habitat destruction. Known for its docile behavior, this species is endangered and restricted to salt marshes bordering San Francisco Bay. Although they are good swimmers, they prefer the dense cover offered by pickleweed, a key component of these salt marshes.
HOUSE MOUSE Mus musculus 130–200mm, 65–100mm, 18–23g
Small, nearly unicolored grayish-brown mouse with dark underparts. Tail is dusky and unicolored. Most likely to be confused with the Harvest Mouse, which has grooved incisors and typically has reddish back and lighter belly, or Peromyscus, which has white underparts. This cosmopolitan, introduced species is most common around human habitations, but may inhabit old fields and nearby disturbed habitats as well.
PLATE 52
NORTHERN DEERMICE
PEROMYSCUS MICE - Mice in this diverse group are characterized by brownish backs, white bellies, and long tails. Their large eyes and ears are adaptations to their nocturnal habits. The different species are distinguished by details of their measurements, and body and tail coloration.
WHITE-FOOTED DEERMOUSE Peromyscus leucopus 150–205mm, 65–95mm, 15–25g
Small, grayish to brownish mouse, frequently with dark stripe along mid-back, and white underparts. Tail sparsely haired and indistinctly bicolored, tuft of hairs on tip less than 5mm long. Very similar to other species of Peromyscus: North American Deermouse typically has a distinctly bicolored tail (although not in the northeastern United States); Cotton Deermouse has a longer hind foot; Oldfield Deermouse is smaller and pale cinnamon to almost white in color, and Brush, White-ankled, Piõn, Saxicoline, Northern Rock, and Texas Deermouse all have longer tails. Favors warm dry forests at low to mid-elevations. This is the most common Peromyscus in eastern mixed deciduous and coniferous forests, and it also frequents the edges of agricultural areas, where it forages in the fields.
NORTH AMERICAN DEERMOUSE Peromyscus maniculatus 120–225mm, 50–125mm, 10–30g
The most widespread, geographically and ecologically variable mouse in North America. Has large black bulging eyes, relatively large, naked ears, fine, smooth-lying fur, and white feet. The well-haired, sharply bicolored tail is tipped with a tuft of short, stiff, hairs something like a watercolor brush. Juveniles are gray, subadults are yellowish brown. The two main forms include a long-tailed, large-eared forest dweller and a short-tailed, small-eared, open-country form. Generally has darker, richer colors in humid regions and paler, drabber colors in arid regions. Differs from White-footed Deermouse by having a distinctly bicolored tail that is about as long as the head and body length; from Northwestern Deermouse by having a shorter tail and foot; from Brush and White-ankled Deermouse by having a shorter tail; from California Deermouse by being smaller; from Cactus and Merriam’s Deermouse by being darker in color with more hair on tail and more distinctly bicolored tail; from Canyon Deermouse by having darker color, shorter tail, and shorter, less soft pelage; and from Piõn and Northern Rock Deermouse by having smaller ears. Found in almost all habitat types within its range.
NORTHWESTERN DEERMOUSE Peromyscus keeni 181–236mm, 92–114mm, 10–30g
Large mouse with dark colors, long tail, and dense fur. Similar to North American Deermouse, but significantly larger, and with a longer tail. Agile jumpers, they also are capable of climbing into lower vegetation. The breeding season is April–June, and litters of 4–7 are normal. This is the most common deermouse along the Canadian Pacific coast, where it occupies habitats ranging from coastal lowlands to subalpine forests. Tends to be more common in edge habitats, and less so in dense coniferous forests. They frequently occupy buildings, especially in rural areas during winter.
PLATE 53
SOUTHEASTERN PEROMYSCUS AND RELATIVES
COTTON DEERMOUSE Peromyscus gossypinus 142–206mm, 55–97mm, 17–46g
Medium-sized Peromyscus, dark golden brown above with white underparts and feet. Mid-dorsal area is dusky. Soles of feet have prominent ridges. Tail is shorter than head and body, sparsely haired and dark on upper surface but fading to white underneath. Young animals are grayer. Larger than Oldfield and North American Deermouse. Also larger than White-footed Deermice of the same age. The subspecies from Key Largo(P. g. allapaticola) is endangered. Good climbers and swimmers, they prefer somewhat wet habitats, especially bottomland hardwood forests, hammocks, and swamps, although they also inhabit drier upland habitats, and sometimes enter buildings.
OLDFIELD DEERMOUSE Peromyscus polionotus 110–150mm, 40–60mm, 10–15g
Small Peromyscus whose inland forms are fawn-colored or brownish gray dorsally, slightly darker along the midline with hairs that are slate-gray at the base. Underparts are white with hairs pigmented at the base, and the bicolored tail has a dark dorsal stripe. Beach forms are paler and have underparts that are white to the base of the hairs, and a dark tail stripe that is reduced or absent. Many coastal subspecies are Endangered because of the declining health of the Gulf states’ coastal dune ecosystem. Inhabits open, sandy habitats in early successional stages of abandoned fields, and grassy dunes along the coast.
FLORIDA DEERMOUSE Podomys floridanus 178–220mm, 80–101mm, 27–47g
Large mouse; brownish above, and white below, with orange lateral areas separating the two. Larger than other Peromyscus in range, with bigger ears and feet. Has orange color on cheeks, shoulders, and sides. Has a distinctive skunklike odor. Known to frequent burrows of gopher tortoises, where they build side tunnels off the main burrow. They reproduce year-round with litters of 1–5 weighing 2–3g each after a gestation period of about 23 days. The diet includes acorns and other plants such as paw-paw, plus insects. Uses sandy uplands with prickly pear cactus and longleaf pines.
GOLDEN MOUSE Ochrotomys nuttalli 140–190mm, 67–97mm, 18–27g
Medium-sized mouse with golden upperparts and creamy-colored underparts and feet. Pelage is very soft and hairs are very fine. Attractive and relatively docile. Degree of brightness of color varies by subspecies. Tail semi-prehensile and used in climbing, as this species is fairly arboreal and builds nests and feeding platforms in vines, trees, and Spanish moss. They feed on seeds, nuts, and berries of plants such as Sumac, cherry, dogwood, blackberry, and greenbrier, as well as occasional invertebrates. Uses densely forested lowlands and floodplain communities, often including honeysuckle, greenbrier, or other vines. Rarely encountered in or near human habitations.
PLATE 54
FAR WEST PEROMYSCUS
CALIFORNIA DEERMOUSE Peromyscus californicus 220–285mm, 117–156mm, 33–55g
The largest Peromyscus; has long, dense, fine fur that varies from yellowish brown to gray with a blackish-brown back and grayish below. The tail is indistinctly bicolored, well haired, and longer than the head and body. Uses chaparral and oak woodland, redwood forests, and coastal sage scrub.
CANYON DEERMOUSE Peromyscus crinitus 162–191mm, 79–118mm, 13–23g
Small to medium-sized mouse with rel
atively long ears. The tail is as long as the head and body and thinly haired with a distinct “pencil” of hairs at the tip. Venter is white, sometimes with a buff pectoral or anal patch. Feet are white. Tail is more tufted and densely haired than in Merriam’s or Cactus Deermouse. Uses arid grasslands and shrublands, and slickrock deserts of west.
CACTUS DEERMOUSE Peromyscus eremicus 169–218mm, 92–117mm, 18–40g
Medium-sized mouse with long, soft, silky pelage and large ears. Body is pale gray washed with reddish brown above and whitish on the underparts. The head is grayish, and the lateral line is pale yellowish buff. Smaller and grayer than the California Deermouse with a lateral line and less hair on the tail. Usually smaller than the Merriam’s Deermouse and lighter in color, with white (not creamy) underparts and without a cinnamon-colored pectoral patch. Lacks the densely-haired tail with tufted tip of the Brush or Canyon Deermouse. Uses low desert areas and rocky foothills with scattered vegetation and sandy soils(see red area on map).
Mammals of North America Page 10