In woods and thickets, where birds abound
most, they are continually losing sight of each other, and are only
prevented from scattering by calling often; while the muffling effect on
sound of the close foliage, to' which may be added a spirit of emulation
where many voices are heard, incites most species, especially those that
are social, to exert their voices to the utmost pitch in singing,
calling, and screaming. On the open pampas, birds, which are not
compelled to live concealed on the surface, can see each other at long
distances, and perpetual calling is not needful: moreover, in that still
atmosphere sound travels far. As a rule their voices are strangely
subdued; nature's silence has infected them, and they have become silent
by habit. This is not the case with aquatic species, which are nearly
all migrants from noisier regions, and mass themselves in lagoons and
marshes, where they are all loquacious together. It is also noteworthy
that the subdued bird-voices, some of which are exceedingly sweet and
expressive, and the notes of many of the insects and batrachians have a
great resemblance, and seem to be in accord with the aeolian tones of
the wind in reeds and grasses: a stranger to the pampas, even a
naturalist accustomed to a different fauna, will often find it hard to
distinguish between bird, frog, and insect voices.
The mammalia is poor in species, and with the single exception of the
well-known vizcacha (Lagostomus trichodactylus), there is not one of
which it can truly be said that it is in any special way the product of
the pampas, or, in other words, that its instincts are better suited to
the conditions of the pampas than to those of other districts.
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