The homes of small mammals vary greatly. The species living in
underground burrows usually excavate an oval chamber which is filled
with fine vegetable material to form a snug retreat. The muskrat places
a conical lodge on the border of a marshy stream or lake. The wood-rat
lives in an underground burrow, in a nest of sticks and trash heaped
above the ground or in a stick nest placed among the branches of low
trees. Harvest mice build a little hollow ball of grass blades, lined
with finer material, among the branches of bushes several feet above
the ground. White-footed mice may lodge in a knot-hole 50 feet or more
above ground in the trunk of a tree.
As a rule, small mammals are of inconspicuous colors which harmonize
so well with their surroundings that when not in motion, especially
if lying close to the ground, they are difficult to distinguish.
Exceptions to this rule are obvious in the case of jack-rabbits when
standing on bare plains, or other mammals which are apart from the
usual partly concealing growth of vegetation or other surroundings.
In contrast to the protective coloration are certain markings, like the
cottony white underside of the tail of the cottontail rabbit, which
renders the flight of this animal conspicuous in the gloomiest shades
of the forest, or even on the approach of night, when it is impossible
to distinguish the animal itself. The white underside of the tail of
the antelope chipmunk is another well-defined instance of this kind.