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Mammal Checklists of the United States

Rocky Mountain Arsenal National Wildlife Refuge

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Commerce City, Colorado


The Rocky Mountain Arsenal National Wildlife Refuge offers a unique opportunity for wildlife watchers. Located only 10 miles northeast of Denver, Colorado, this 27-square-mile site provides habitat for nearly 300 animal species. The Refuge's mammals come in a great variety, from the social black-tailed prairie dog to the elusive coyote.

Mammals have characteristics that distinguish them from other animals. They have hair (often called fur), control their body temperature, and nurture their young. Almost all mammals give birth instead of laying eggs.

Spotting mammals can be challenging. They are highly mobile. They walk, run, burrow, climb, and swim; some even fly. The time of day they are active varies by species. Some travel at dawn and dusk, while others move in the dark of night (nocturnal) or broad daylight. These traits test a wildlife watcher's observation skills. Tracks, droppings (scat), food remnants, burrows, tunnels, and trails through vegetation are clues that mammals have been in an area.

Prairie dogs and mule and white-tailed deer are commonly seen at the Refuge. Prairie dog pups emerge from their burrows in early May and display playful antics around the "town." In May and June, deer fawns explore their new grassland and woodland homes. Coyotes may be seen year-round, usually hunting in prairie dog towns.

Wildlife Watching Tips

Wildlife watching at the Refuge can be a rewarding experience if you respect the wildlife and practice proper wildlife watching etiquette. These viewing tips are suggested to protect the wildlife and improve your visit to the Refuge.

This list provides the common and scientific names, as well as a brief description, of the 32 mammals sighted at the Refuge. The Refuge supports three primary habitats which meet their needs for survival - wetlands, woodlands, and grasslands. The code system reflects the relative abundance of each mammal at the Refuge. The likelihood that you will observe a mammal in its habitat may be inferred from the code it receives. Many mammal utilize more than one habitat and are indicated as such on the list.

W - Wetlands
F - Woodlands
G - Grasslands

C - Common
U - Uncommon
R - Rare
* - although common, not easily observed because of its behaviors, size, and/or habitat

RABBITS & HARES W F G Eastern cottontail - c u (Sylvilagus floridanus) Grayish-brown fur with a cottonball-like tail; smaller ears (2-3 inches) than hares. Male eastern cottontails fight and dance to win females. This favored prey of raptors and coyotes jumps sideways to lose its scent when fleeing predators. Desert cottontail - u c (Sylvilagus audubonii) Buff-brown fur with a bright rust-colored nape; medium-sized ears. The desert cottontail has been known to climb low, sloping trees to nest. It may be found resting in prairie dog burrows. Black-tailed jackrabbit - - c (Lepus californicus) Sand-colored fur peppered with black; black stripe on tail extending onto rump; long ears (4-5 inches) with black tips. This true hare's long hind legs enable it to maintain speeds of 30-35 mph over short distances. Its long ears help regulate its body temperature. As with deer, females are called does, and males are called bucks.
RODENTS W F G Black-tailed prairie dog - - c (Cynomys ludovicianus) Stout body with yellow-to-gray fur and buffy underparts; short, black-tipped tail. This social animal lives in underground burrows in prairie dog "towns." It is commonly seen feeding or sitting atop a burrow in a look-out position. Prairie dogs do not hibernate during the winter; therefore, they provide a year-round food source for the Refuge's diverse raptor population. Northern pocket gopher - c* c* (Thomomys talpoides) Color varies greatly from rich brown to yellowish-brown or grayish; small, round ears; small eyes; long front claws. This small rodent is rarely seen aboveground. Designed for life underground, it has fur that can lie forward or backward for easy movement in a tunnel. It uses its fur-lined cheek pouches for carrying food (grasses and roots) or dirt. Plains pocket gopher - - c* (Geomys bursarius) Brown fur with pale underbelly; long claws; long, almost hairless tail; white feet. This rodent's lips close behind its front incisors to keep dirt out of its mouth while digging. Its fur-lined cheek pouches serve as temporary storage units for food or dirt. Because it spends its life underground, dirt mounds left behind during burrowing may be the only way of knowing of its presence. Eastern fox squirrel - c - (Sciurus niger) Gray, brown, or reddish fur; buff-colored underparts; bushy tail. The largest member of the tree squirrel family, the eastern fox squirrel is active during early morning and late afternoons. It builds a nest of sticks and leaves in trees during the summer and spends the winter in a tree hole nest. Muskrat c* - - (Ondatra zibethicus) Silvery brown-to-black fur; small eyes; long tail, flattened vertically. The muskrat's adaptations to wetland life include a rudder-like tail, webbed hindfeet, and lips that close behind incisors for carrying food underwater. Porcupine - r - (Erethizon dorsatum) Large, chunky body; short legs; long, yellowish guard hairs on front half of body; quills on rump and tail. This unique mammal is protected from predators by its quills (about 30,000). It lives mainly in trees. Deer mouse c* c* c* (Peromyscus maniculatus) Grayish to reddish-brown above; white belly; bi-colored and short-haired tail. It is nocturnal, foraging for nuts, insects and seeds at night. Western harvest mouse u* - c* (Reithrodontomys megalotis) Brownish above; buff along sides; white below. The western harvest mouse is active at night and is known to huddle with others for warmth. It is an important food source for Refuge predators. Hispid pocket mouse - - c* (Perognathus hispidus) Upper body parts pale yellow to gray, white underbody; short tail; larger than other mice. The hispid pocket mouse lives in burrows with branches for food storage and a maternity neet. It uses fur-lined cheek pouches for carrying food, similar to pocket gophers. Ord's kangaroo rat - - c* (Dipodomys ordii) Distinctive tail spans a greater distance than the length of the head and body; white spots at base of ears and above eyes. This rodent thumps its hind foot as an alarm call and may leap six to eight feet to escape a predator. It does not drink water but metabolizes it from the food it eats. Northern grasshopper mouse - - c* (Onychomys leucogaster) Two color phases: grayish and cinnamon buff, white underbody. Quite ferocious for its size, this rodent is capable of killing scorpions. It is most active on moonless nights or under heavy cloud cover. House mouse - c* c* (Mus musculus) Grayish brown above; almost as dark underneath. Common in your house as well as a wildlife refuge, this opportunistic rodent can establish populations in crop fields or buildings. It is more successful in disturbed areas versus natural areas. Plains pocket mouse - - c* (Perognathus flavescens) Soft, pale yellow-to-dark gray fur; white underparts. This nocturnal rodent is a favorite food of owls. It uses its fur-lined cheek pouches for carrying food, similar to pocket gophers. Silky pocket mouse - - u (Perognathus flavus) Pale yellow; distinctive yellow patch behind ears. The silky pocket mouse's cheek pockets are used for storing food (seeds) from which it metabolizes all of its water. Olive-backed pocket mouse - - u (Perognathus fasciatus) Grizzled olive-gray fur on back; white below, tail slightly less than half the total length of head and body. This pocket mouse digs summer chambers 12-15 inches below the ground surface and winter ones up to six feet deep. Thirteen-lined ground squirrel - - c (Spermophilus tridecemlineatus) Thirteen alternating dark and light longitudinal stripes on back with light spots on the dark stripes; short tail. This small mammal is strictly diurnal (active during the day) and is often observed in and near prairie dog towns. It hibernates, while its prairie dog neighbors remain active all winter. Spotted ground squirrel - r r (Spermophilus spilosoma) Gray or brown fur with small indistinct light spots scattered on back; whitish below, similar in size to thirteen-lined ground squirrel. Meadow vole c* - c* (Microtus pennsylvanicus) Varies in color from yellowish or reddish-brown peppered with black to blackish-brown; tail shorter than the length of the head and body. This rodent is an important prey species. If it reaches adulthood, its life expectancy is three months or less. Prairie vole - - r (Microtus ochrogaster) Grizzled yellowish-brown fur; buff underbody; short tail compared to other voles. This vole inhabits standing dry grass where it builds a system of feeding tunnels with food storage areas. Its tunnels look like ditches in grass. Grass nests are often found at the ends of trails. Prairie vole populations have been found to peak and then decline every three to four years.
CARNIVORES W F G Long-tailed weasel u u u (Mustela frenata) Summer: brown with white underparts. Winter: all white with black tail tip. Long-tailed weasels use a variety of habitats but prefer to be near water. They are completely carnivorous (meat-eating). Mink r - - (Mustela vison) Almost entirely brown, somewhat darker on back; white chin; black tail tip. Like its relatives the skunk and the badger, the mink can emit a strong odor. It lives near wetlands such as rivers, creeks, lakes, ponds, and marshes. Coyote c c c (Canis latrans) Gray with buff underparts; tip of tail usually black. The Refuge's largest predator, the coyote is an adept and opportunistic hunter. It is frequently seen hunting in prairie dog towns near dusk. Red fox u u u (Vulpes vulpes) Rusty-reddish fur with white underparts, chin, and throat; white-tipped tail. It lives in many habitats but is generally found in densely vegetated areas. Coyotes out-compete foxes and frequently kill them. Badger - u c* (Taxidea taxus) Body wider than it is high; white stripe runs along back from nose to shoulder; black patches on cheeks. The badger lives in dry, open country. It feeds on rodents by excavating burrows with its large foreclaws. Raccoon r r - (Procyon lotor) Gray to almost black with five to 10 rings on well-furred tail; black mask. The characteristic "bandit" mask across the raccoon's eyes is easily recognizable. Because it uses its well developed sense of touch to find creatures in the water, it appears to be "washing" its food. Striped skunk - u u (Mephitis mephitis) White band on back of head and nape splits into two broad stripes down back; black tail may have a white tip or fringe. The skunk uses two glands under its tail to spray musk when it is alarmed. Its distinctive coloration warns other animals to keep their distance. The skunk is active at dusk and night.
DEER Mule deer c c c (Odocoileus hemionus) Tail white above with black tip; very large ears; buck's antlers branch repeatedly. The mule deer is one of the most common and visible mammals at the Refuge. Native to the West, it is a grassland species that likes open areas and is not overly skittish It uses a stiff-legged bound, called a "stot," when fleeing. White-tailed deer c c u (Odocoileus virginianus) Tail down at rest, appearing brown with white fringe; tail displayed like a flag when fleeing, showing bright white underside; buck's antlers have one main beam with unbranched tines (points). An eastern species that has moved west, the white-tailed deer spends more time in wooded areas than the mule deer.
SHREWS W F G Least shrew - - u (Cryptotis parva) Brownish gray to black; white underparts; pointed snout; small eyes and hidden ears. This social mammal inhabits open grassy fields where it uses burrows made by other animals and lives in colonies. Measuring approximately three inches in total length, this shrew is the smallest mammal at the Refuge. It is very active, resting from foraging and digging only periodically.

For additional information contact:
                       Rocky Mountain Arsenal NWR
                       Building 613
                       Commerce City, Colorado 80022           
                       Telephone: 303/289-0232
This resource is based on the following source:
U.S. Fish and Wildlife Service.  1994.  Mammals of Rocky Mountain Arsenal 
     National Wildlife Refuge.  U.S. Fish and Wildlife Service.  Unpaginated.
This resource should be cited as:
U.S. Fish and Wildlife Service.  1994.  Mammals of Rocky Mountain Arsenal 
     National Wildlife Refuge.  U.S. Fish and Wildlife Service.  Unpaginated.  
     Jamestown, ND: Northern Prairie Wildlife Research Center Online.
     (Version 22MAY98).

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