Rocky Mountain National Park, Colorado

by Edwin C. Alberts

Gnawing Mammals

The YELLOWBELLY MARMOT, with its reddish underparts, grizzled back, and bushy tail, is seen by nearly all park visitors. Although it is more common in medium altitudes in the mountains, it also may be seen high along Trail Ridge Road, and a pair, reportedly, is living atop Longs Peak! These rodents live in dens, usually rockpiles, into which they pack twigs and grass to make a comfortable nest. They store up a heavy layer of fat in the summer and hibernate during the cold winter. Their natural food consists of grasses, berries, and roots. Their short, sharp whistle can be heard a mile away. During the summer, hikers occasionally see rather humanlike scenes, as marmot families sun themselves on the “front porches” of their rockpile homes.

The TASSEL-EARED, or ABERT, SQUIRREL is an excellent example of the zonal specialization of mammals. It is almost entirely restricted to the ponderosa pine forest belt. Its showy ear tufts, although often absent during the summer, set it apart from other local squirrels. It feeds mostly on ponderosa pine seeds, the bark of twigs and young trees of this species, and such wild fruits and succulent vegetation as are available. The Abert squirrel builds nests in the trees and is a familiar sight to hikers in the ponderosa pine forests. It is usually gray-colored, but may be brown or even completely black.

Another small arboreal rodent, the SPRUCE SQUIRREL, chatters and scolds when a stranger enters its patch of forest. It roams both the lodgepole pine and higher spruce-fir forests with their bitter winters, yet it does not hibernate. Even after the most severe storms it will emerge to travel through the treetop world it occupies. Some bird enthusiasts have little regard for it, because of its habit of eating eggs and young birds whenever the opportunity presents itself. However, in a National Park the squirrel’s desire to live is considered to be as important as is the bird’s. A certain “balance” of population is the result, which is, after all, one of the desirable features in an area dedicated to preserving natural conditions.

CHIPMUNKS are particularly familiar at Trail Ridge Road parking areas. These small squirrels are reddish-brown above, with white underparts and with four white stripes running along the back. A definite stripe across the face distinguishes them from the golden-mantled ground squirrels, with which they are often found.

The GOLDEN-MANTLED GROUND SQUIRREL is often confused with the smaller chipmunks which it joins in begging for visitor handouts at parking areas below treeline on Trail Ridge Road. Its natural food is succulent plant material and seeds, but many of the gregarious little animals are becoming more or less dependent upon food offered them by humans. You can see them most conveniently at Many Parks Curve.

Another little rodent, common in the lower meadows, is the RICHARDSON GROUND SQUIRREL (“picket pin”). It lives in colonies, after the fashion of the prairie dog of the plains. It is abundant in Moraine Park.

Relatively few park visitors see the BEAVER; but all can see examples of its work. It works at night as a rule, and usually remains out of sight when humans are abroad. These industrious rodents are much larger than the related chipmunks and marmots, and weigh as much as 90 pounds. Beaver pelts were part of the lure that led to the early exploration of the West. Almost exterminated about 50 years ago, they are now relatively abundant in Rocky Mountain National Park.

Yellowbelly marmot—seen by most visitors.

The beaver is well adapted to its water environment. The hindlegs are webbed for efficient swimming; the tail, broad and horizontally flattened, helps in underwater maneuvering. However, its swimming speed at the surface of the water is only about 2 miles per hour. Beaver can remain submerged for over 5 minutes; this ability helps in escaping enemies.

The beaver is sometimes seen by alert observers in late afternoon or early morning.

Beaver dams are abundant in the park. Many typical examples can be seen in Horseshoe Park, Moraine Park, Glacier Basin, and Hidden Valley, and along the Colorado River. Nearly all of the park trails pass beaver workings. The dams are built of various materials in this region, but most commonly of mud, parts of aspens, and debris. They are started from the upstream side—usually on shallow creeks—and as the water level rises so does the dam. The beaver uses its front paws almost as hands. The load of mud or sticks sometimes is carried by being pressed against the chest as the animal walks on its hind feet to the top of the structure it is building. The dam is made to create a stabilized water level. This is essential for protection of the beaver’s island den—a lodge made of sticks and mud. The beaver house starts as a solid heap of debris, but the animal chews and digs out a couple of underwater tunnels, as well as one or more dome-shaped rooms with the floor a few inches above water level. In this dry retreat the beaver rests, sleeps, and rears its family. Few natural enemies can pursue it through the underwater entrances. Its food is chiefly aspen bark and twigs. A winter supply is stored under water during late summer.

Because of its energy, skill, and persistence, the beaver has become a symbol of industriousness. It is also often credited with more intelligence than it probably possesses. Its apparent industry and resourcefulness are due more likely to inherited instincts than to reasoning. At any rate, this large rodent is surely one of the most interesting animals in the park.

A narrow tail distinguishes the muskrat from the beaver, which may live in the same locality.

The MUSKRAT is frequently active in daylight hours. It lives in the same environment as the beaver, but in the park has a much more limited distribution and is confined to lower elevations. It builds lodges, too; they are much smaller than those of the beaver, and are largely composed of mud and plant material. The lodge serves as a secondary food source in the winter, and many muskrat houses are practically eaten away by spring. Unlike the beaver, a strict vegetarian, the muskrat eats fish, insects, and any birds it can catch, as well as plant food. This animal has not acquired the ability to build dams, but does make rafts of sticks and twigs. When seen closely, a muskrat is easily distinguished from a beaver, for it is smaller and has a slender, vertically flattened tail, quite unlike that of the beaver.

Probably everyone recognizes the PORCUPINE. It is a large, short-legged rodent, rather clumsy of behavior, and usually seen either sleeping or leisurely chewing the bark of a tree. The porcupine survives, despite its sluggish behavior, because of the protection afforded by some 30,000 quills in its pelage. Although it cannot “throw” these quills, they are very loosely attached, and when the tail is vigorously thrashed about it is inevitable that some of the quills become detached and fall away. The unlucky recipient of such a slap of the tail will be convinced that the quills were thrown, although the effective embedding of quills is done by direct contact.

The MOUNTAIN COTTONTAIL is often seen in the lower forests. Despite heavy predation by many natural enemies, the cottontail manages to maintain itself because of its high birth rate. One mother may produce a total of 25 young in the 4 or 5 litters born during the year. It is fairly small, grayish-brown in color, with rather short ears and a conspicuous cottony tail resembling a powder puff. It lives in underground burrows and retains the same color winter and summer.

The SNOWSHOE HARE nests on the surface of the ground. Its fur changes from grayish-brown in summer to white in winter. A denizen of the spruce-fir and lodgepole pine forests and of the tundra, it hops about the snow on its huge, furry, “snowshoe” feet, apparently finding the severe winters of the high country no great hardship. It is not common in the park, and therefore is not often seen.

Porcupine.

Friendly chipmunks make themselves known throughout the park.

Motorists on the highest parts of the Trail Ridge Road often see the PIKA, which looks like a small, grayish guinea pig but is really a close relative of the rabbit. It is found in the rock slides and talus piles in the high country mostly above treeline, and is seldom seen below 9,000 feet. Despite the subzero temperature of the tundra belt, it does not hibernate. Its habit of storing little bundles of mountain grasses and other alpine plants has given it the nickname of “alpine haymaker”; it is also sometimes called “cony”—a name better reserved for an unrelated Old World mammal. Look for the pika at Rock Cut on Trail Ridge Road, it seems to have favorite sunning spots from which it greets the traveler with shrill shrieks.