The most marked of all examples of “directive” coloration among the
small mammals appears to be that of certain white-sided jack-rabbits,
in which the white areas on the sides and rump are drawn up and down
as the animal runs across the plains, giving a flashing effect, which
attracts attention to them exactly as does the white rump-patch of the
antelope.
In the northern part of the continent, where snow lies for many months,
several species of hares are dusky or buffy gray in summer and change
to a pure white coat in winter. This change is of enormous protective
value to these animals. In Greenland, where the summer is short and
snow exists throughout the year, the highest northern representative
of the hares remains permanently white, while near the southern border
of snow in the United States the varying hares and white-tailed
jack-rabbits, which become pure white in the northern parts of their
range, make only a partial change.
Weasels are the only carnivores which change from the brown of summer
to a white winter coat. Owing to their small size and the need for
activity in the snowy northern regions, where they would be peculiarly
susceptible to danger from birds of prey and larger predatory animals,
their protective white coats serve them well.
It was formerly considered that the change of mammals from the brown of
summer to the white winter coat in the fall, and from the white to the
brown in spring, was due to a change in the color of the hairs, but it
is now known that it is entirely due to molt. The time of these changes
depends on the season, and this varies several weeks, according to
whether the fall or spring is early or late.
The general shades of mammals are of delicate tints, and the spots,
stripes, and other markings, as in the case of chipmunks and the little
spotted skunk, are often of great beauty.