Small mammals vary greatly in their vocal powers, but the changes in
intonation and character of the notes and calls indicate plainly that
they are used to convey a variety of meanings.
Some are practically voiceless, as in the case of rabbits and hares,
except when in an extremity of fear they utter loud shrieks of terror.
Squirrels, prairie-dogs, and some other small mammals bark and chatter,
while mice and bats have a variety of curious squeaking notes. Marmots
and ground-squirrels have chattering notes and sharp, whistling calls.
In addition, some of the squirrels and many mice are known to have
continuous series of notes which are as evidently songs as the
utterances of birds. Some of these notes, as in the case of singing
mice, have a remarkably musical character, similar to the warblings of
canaries. Various unrelated species of mice have been observed singing,
and a closer study of the life habits of these small animals may
develop the fact that all are songsters to some degree.
House rats and mice have, undoubtedly, been parasitic about the
haunts of man from early times. From Asia they have accompanied him
through his advance in civilization. With the growth of commerce they
have traveled around the world, becoming transplanted to all lands
and thriving in all climates. In various parts of America they have
not only become pests about human habitations, but where climatic
conditions were favorable have reverted to the wild state and are
competing with the native species in the fields.
Of all the small mammals none have become modified to such an extent
as the bats. As a group these mammals are of world-wide distribution
except in the inhospitable polar regions. They are true mammals and
present an extraordinary variation in size, from tiny little creatures,
almost as small and fragile as butterflies, to the huge fruit-bats,
with a spread of wings like that of a wild goose.