  Family:
Rodentia |
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Rodents:
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
Castoridae
- 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.