The Desert Pampas. 9 
are comparatively very silent; even those belonging 
to groups which elsewhere are highly loquacious. 
The reason of this is not far to seek. 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, especi- 
ally 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 need- 
ful: moreover, in that still atmosphere sound travels 
far. Asa 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 solian 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 
