Abert’s or Tassel-eared Squirrel (Sciurus aberti)

One of several subspecies of Tassel-eared squirrels, Abert’s are charming and beloved squirrels found primarily in Ponderosa forests. These delightful critters are common in the Evergreen area. They are identified by their large size and the long hair on their ears.

Read more about them here: The Prince of the Ponderosa Pines: Our Evergreen Tassel-Eared Squirrels (Evergreen Audubon)

Black-tailed Prairie Dog (Cynomys ludovicianus)

Prairie Dogs are found in a few places near the Bear Creek watershed, including at the Dinosaur Ridge visitor center in Morrison, and at the Denver Botanical Gardens at Chatfield Farms, across from Chatfield State Park. Prairie Dog colonies are also easy to spot by the side of the highway near Denver International Airport and along I25 both north and south of Denver.

Prairie Dogs are tan with a whitish or buff-white bellies. The tips of their tails are black, and they have exceedingly small ears for their size. Full grown, they are 14 to 17 inches long and weigh between 2 and 3 pounds.

Prairie Dogs live in colonies called “towns” on dry, flat, sparsely vegetated grasslands where they build complex underground tunnels and chambers, as deep as 15 feet. They mound earth around the entrances to their burrows to keep them from flooding. Prairie Dogs keep the prairie plants in their towns trimmed to 6 inches or less so that they can easily spot predators when standing sentry on their mounds. Prairie Dogs, which are rodents, not dogs, got their name because they communicate danger with dog-like barks.

Also worth knowing: Settlers and ranchers mistakenly believed that Prairie Dogs destroyed crops and that their tunnels were dangerous to livestock. In fact, Prairie Dogs are an important “keystone” species, making it possible for other animals and plants in their ecosystem to survive and thrive.

For more information about Prairie Dogs, go to: Black-Tailed Prairie Dog (Smithsonian’s National Zoo & Conservation Institute)

Colorado Chipmunk (Tamias quadrivittatus) and the Least Chipmunk (Tamias minimus)

There are several species of Chipmunk in Colorado but these are the two chipmunks commonly found in the Bear Creek Watershed. Chipmunks have stripes that go from their noses to their tails. They eat seeds, berries, nuts, fruits, and insects. They are quick, nervous little animals, always looking out for predators while stuffing their cheeks with seeks and nuts. Chipmunks don’t actually hibernate, but they are not seen much during cold weather. They survive winter by going into torpor (a state of decreased activity, reduced body temperature and lower metabolic rate) in their burrows for long stretches, waking up occasionally and snacking on food that they have stored.

The Colorado chipmunk is the larger of the two, with adults measuring about 9 inches, including their tails, and weighing about 2 ounces. A full-grown Least chipmunk will only be about 7 ½ inches long and weigh around 1 to 1 ½ ounces. Colorado chipmunks’ stripes are nearly black; the stripes on the Least are more gray. Colorado chipmunks; stripe taper off before reaching the tail; Least chipmunks’ go all that way to the base of the tail. Colorado chipmunks wag their tails from side to side while making small “chip chip” vocalizations. Least Chipmunks which flick their tails up and down. Least chipmunks prefer open areas such as forest edges and clearings. They are also found near rock cliffs, river bluffs and open jack pine stands. Colorado chipmunks are found in Ponderosa Pine, Douglas fir and Aspen forests.

For more information about Chipmunks and Squirrels, go to: Squirrels and Chipmunks (National Park Service)
or
Squirrel Refuge

Fox Squirrel (Sciurus niger)

Fox Squirrels are the largest tree squirrels. While they were not originally found in Colorado, they have been here for centuries and are common along the front range, anywhere where there are trees. Fox Squirrel are plentiful in city parks and residential neighborhoods. They are easy to identify by their large size, yellowish-brown fur, and brownish-orange tummies. They average 17 to 28 inches in length with 8 to 13-inch-long tails. They can weigh more than 2 pounds. They are only active during the day. They eat seeds, nuts, insects, bird eggs and nestlings, flowers, and buds.

Golden Mantled Ground Squirrel (Spermophilus lateralis)

Golden-Mantled Ground Squirrels are larger than chipmunks. Their faces are not striped, and they have relatively short tails. They have gold colored shoulders. Like chipmunks, they have cheek pouches for carrying food. They are found from low elevations to above tree line, among rocks and near the edges of wooded areas.

Muskrat (Ondatra zibethicus)

Muskrats are medium-sized rodents found near wetlands, lakes, ponds and streams. Mature muskrats weigh up to 4 pounds and measure 8 to 10 inches plus their tails, which are half again as long. They have short, brown fur and long, naked, rat-like tails. Muskrats spend most of their time in the water and can hold their breath under water for up to 15 minutes! They are primarily vegetarian but will also eat small animals such as crayfish and frogs.
Evergreen Nature Center has a family of muskrats that lives in a den at the edge of Evergreen Lake, directly under the Nature Center. Accustomed to rental boat traffic and groups of nature center visitors, our neighborhood muskrats can often be seen going about the business of raising and feeding a family.

For more information about Muskrats, go to: Muskrat (Encyclopedia.com)

Also worth knowing: The best way to sort out muskrats from other aquatic mammals is to pay attention to size. Muskrats are smaller than Beavers and larger than Ermine and Long-tailed weasels. Also note how they use their tails. You can usually see a muskrat’s tail because it rides on or near the surface of the water and wags back and forth in a S motion, propelling the animal forward. It is much more difficult to see a Beaver or Otter’s tail.

North American Beaver (Castor Canadensis)

The largest rodents in North America, mature Beavers can weigh 50-55 pounds or more. They are found in and near lakes, streams and ponds, in areas with abundant trees. They have short legs and webbed feet, making them awkward on land but expert swimmers. They have broad, flat, hairless tails that they use to propel themselves in the water.

Beavers cut down trees using remarkably sharp teeth and strong jaws, then use the trunks and branches to build lodges and dams in lakes, ponds and streams, often impounding water and causing flooding. Vegetarians, they store leafy branches and tender twigs near their underwater dens to eat year-round. Beavers are primarily nocturnal but may also be active during the day. Freshly gnawed tree stumps are a sure sign that there are beavers nearby.

For more information about Beavers go to:About Beavers (Wetlands and Wildlife) or Beavers (Paws)

North American Porcupine (Erethizon dorsatum)

Full-grown porcupines are unmistakable with their sharp, needle-like quills. Porcupines may be as big as 32 inches long and weigh up to 33 pounds. Their quills are made of keratin, like our fingernails. They have long, sharp claws which make it easy for them dig and to climb trees. These slow-moving creatures like to chill in tall trees, resting on stout branches, tucked in near the trunk. They harvest leaves, twigs, and bark for food, often killing the tree in the process. Mostly nocturnal, porcupines are occasionally active during the day as well.

Porcupines don’t throw their quills. When threatened, they lift and shake their quills. If that doesn’t deter the threat, they jump at the other animal with incredible speed, impaling it with as many as hundreds of sharp, barbed quills. Porcupines have around 30,000 quills. Lost quills grow back, but in the meantime, there are still plenty available if needed.

For more information about Porcupines, go to: North American Porcupine (Smithsonian’s National Zoo & Conservation Institute)

Pine Squirrel (Tamiasciurus hudsonicus)

Pine squirrels, also called Chickarees or Red Squirrels, are small gray tree squirrels, measuring 11-14 inches long, including their tails, and weighing 7-8 ounces. They are gray in winter and reddish gray in the summer, with white tummies, bushy tails, and white eye rings. Known as chatterboxes, they are active and feisty little critters, who spend time defending their territories and scolding intruders.

Pine squirrels eat seeds and nuts, fungi, plants, insects and bird eggs. They don’t hibernate but rely on pinecones collected throughout the summer and fall to see them through the winter. Piles of scales from stripped cones found near the base of conifers are sure signs that there are Pine Squirrels in the area.
Also worth knowing: The name Tamiasciurus means “hoarder squirrel.” The piles of pine cone parts are called “middens” and can be several feet wide and 5 or more feet high.

For more information about Pine Squirrels, go to: American Red Squirrel (Animalia)

Rock Squirrel (Spermophilus variegatus

Rock squirrels are large ground squirrels, measuring up to 12 inches long with 8-inch tails. They can weigh up to 1 ½ pounds and tend to look chubby. They are speckled grayish brown. They have distinct light-colored rings around their eyes, pointy ears, and fluffy squirrel tails. Rock Squirrels eat leaves, stems, seeds, acorns, nuts, fruits, grasshoppers, beetles, and worms. Even though they are ground dwellers, Rock Squirrels can climb nearly as well as tree squirrels.
Rock Squirrels can sometimes be mistaken for Marmots, but, unlike Marmots, Rock Squirrels are found in arid canyons, rocky cliff areas, and boulder piles, in the watershed’s lower elevations. They create complex burrow systems hidden beneath rocks where they den and store food. They often sun themselves on rocks but on very hot days they stay inside and only come out early in the morning and late in the afternoon. They are social and family-oriented living in colonies with several females, immature males, and one dominant male.

For more information about Rock Squirrels, go to: Rock Squirrel (Desert USA)

Yellow-bellied Marmot (Marmota flaviventris)

Yellow-bellied Marmots are found mostly on rocky slopes at higher altitudes, notably along Mt. Evans Road, but they occasionally visit lower altitudes and are sometimes even seen in the Evergreen area. Their brown hair is frosted with white tips making them appear grizzled. They have short, dark bushy tails and white patches on the bridges of the noses/foreheads. Full grown, they weigh up to 11 pounds. Marmots live in burrows in family groups of up to twenty individuals. They are diurnal (mostly active during daylight). They eat plant material, insects, and bird eggs. They hibernate for about 8 months, starting in mid- to late-September.

Also worth knowing: Yellow-bellied Marmots are affectionally known as Whistle Pigs because they communicate with each other with loud, squeaky whistles.

For more information about Yellow-bellied Marmots, go to: Yellow-Bellied Marmot (Animalia)