Most are small, secretive, nocturnal, abundant, and difficult to observe. Without a doubt, the majority of mammals in Idaho are rodents, and about one-third of all mammals, about 1,700 species, are rodents. Their abundance is due partly because they occupy a wide diversity of niches; from tree tops, to undergound burrows, to the water, to human shelter, such as cabins, barns and garages. Their primary distinguishing characteristic is large, ever-growing, chisel-like incisors that occur in pairs in both the upper and lower jaw. These incisors are kept chisel-like because the tips of the upper incisors wear away the tips of the lower ones and vice versa. This keeps them sharp and much like the shape of chisel blade. As primary consumers they are low on the food chain. They also provide many meals for predators and thus have a short life. Only a high reproductive potential overcomes their high mortality. Many rodents have large litters and reproduce up to several times each year. Some rodents, even though they are primarily vegetarians, are also good predators. Many feed on a variety of invertebrate prey, especially insects. Some, such as ground squirrels can be so abundant that they consume crop plants to the excess. Others, such as pocket gophers, may create problems for farmers and ranchers. Overall, though, they are ecologically beneficial and important in most Idaho ecosystems.
Sciuridae - Chipmunks, Marmots and Squirrels
Members of this family represent a large, diverse and interesting group. They live in trees, on the ground, in burrows, and one even glides through the air. Most of us are familiar with the tree squirrels. Their large, bushy tails curl over their body while they are feeding on their nuts, fruits or seeds. We see them in urban areas, or in forests. The flying squirrel, a species of forests is mostly nocturnal and can escape predators by launching out of trees and gliding to the ground or another tree trunk. Other tree squirrels are diurnal, and at best, can only jump short distances from limb to limb. Tree squirrels are non-hibernators. Ground squirrels typically nest in burrows, and most are hibernators. Chipmunks inhabit both trees and the ground. They have internal cheek pouches for transporting food which they store for winter use. They hibernate, but arouse frequently and eat before entering a state of hibernation again. All chipmunks have stripes that run along the sides of their back and extend foreward to their eyes. Most members of the squirrel family vocalize with long, chatter calls or a variety of chirps. There is large range in size, from the smallest chipmunks to the much larger marmots.
Geomyidae - Pocket Gophers
Members of family Geomyidae, the pocket gophers, are fossorial (burrowing) rodents and spend most of their time below ground. They do not hibernate, but rather they store food in underground chambers for use in the winter. During the winter, they are able to expand their range by burrowing into the snow at the surface of thin layers of soil that are too shallow to burrow in during the summer and feed on vegetation. They are named "pocket gophers" because of the external, fur-lined pouches on each side of their cheeks. They carry food and nesting materials in these pouches and literally squeeze the material out with their forepaws.
Heteromyidae - Pocket Mice, Kangaroo Mice and Rats
- American Beaver
The Castoridae family consists of only one species in North America, the American Beaver. A similar species exists in Europe and Asia. They lead an aquatic existence, and are commonly thought of as "nature's engineers" because of their dam and house building capabilities. Fossil evidence shows that a beaver existed during the Pleistocene (ice age) that was as large as a bear.
Muridae - Mice and Rats
Muridae is the largest family of North American mammals, and certainly the largest family in Idaho. They range in size from the very small western harvest mouse weighing ½ of an ounce, to the muskrat, which may weigh 4 pounds. They occupy a great diversity of habitats from the driest area in Idaho to living in a totally aquatic environment. They are generally, non-hibernators, most use burrows for shelter and protection against predators, and they do not have external cheek pouches. Family Muridae is divided into two major groups on the basis of differences in their teeth and body form: the cricetines and the microtines. Cricetines include the harvest mice, deer mice, grasshopper mice and woodrats. They are characterized by having rather long tails, large eyes and ears and cheek teeth with prominent cusps, and most are active at night (nocturnal). Many of these mice are good climbers. The Microtine group includes voles and lemmings. They have stouter, heavier-appearing bodies, and small, inconspicuous eyes and ears, and they have shorter tails. Their cheek teeth are more flattened on top. They tend to be active during day and night, and their populations exhibit dramatic fluctuations; and some exhibit cyclic population fluctuations.
Zapodidae - Jumping mice
Family Zapodidae is a small family consisting of only 4 species. Only one species, the western jumping mouse occurs in Idaho. As their name implies, they have tremendous leaping abilities, much like kangaroo rats. However, they are not closely related to kangaroo rats or pocket mice, but rather they seem more closely related to jerboas of the "Old World" deserts.
Erethizontidae - Porcupine
This is a small family including only eight species. All species are found in the Western Hemisphere, and they all are tree climbers. They have small "bumps" called tubercles, that supposedly give them greater traction when climbing in trees. There is only one species in North America and Idaho.