Nevertheless the creepers are loquacious and have loud
resonant voices; this fact, however, does not really contradict a
well-known principle, for the birds possess the social disposition in an
eminent degree, only the social habit is kept down in them by the
conditions of a life which makes solitude necessary. Thus, a large
proportion of species are found to pair for life; and the only
reasonable explanation of this habit in birds--one which is not very
common in the mammalia--is that such species possess the social temper
or feeling, and live in pairs only because they cannot afford to live in
flocks. Strictly gregarious species pair only for the breeding season.
In the creepers the attachment between the birds thus mated for life is
very great, and, as Azara truly says of Anumbius, so fond of each
other's society are these birds, that when one incubates the other sits
at the entrance to the nest, and when one carries food to its young the
other accompanies it, even if it has found nothing to cany. In these
species that live in pairs, when the two birds are separated they are
perpetually calling to each other, showing how impatient of solitude
they are; while even from the more solitary kind, a high-pitched
call-note is constantly heard in the woods, for these birds, debarred
from associating together, satisfy their instinct by conversing with one
another over long distances.
The foregoing remarks apply to the Dendrocolap-tidae throughout the
temperate countries of South America--the birds inhabiting extensive
grassy plains and marshes, and districts with a scanty or scattered tree
and bush vegetation.
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